HSI1000 Notes - How Science Works PDF

lOMoARcPSD|31354065 HSI1000 Notes How Science Works, Why Science Works (National University of Singapore) Studocu is not sponsored or endorsed by any college or university Downloaded by yunhan ([email protected]) ...

lOMoARcPSD|31354065 HSI1000 Notes How Science Works, Why Science Works (National University of Singapore) Studocu is not sponsored or endorsed by any college or university Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 Lecture 1 - The Founding of Modern Science Chapter 1 - Science Describe what is science and explain the scientific method “in a nut shell” illustrating your explanation with a straightforward example - Science is that activity which aims to further our understanding of why things happen as they do in the natural world. It accomplishes this goal by applications of scientific method—the process of observing nature, isolating a facet that is not well understood and then proposing and testing possible explanations. Science can be applied to anything that has an observable and tangible effect in the world. Scientific Method: 1. Observe 2. Explain 3. Test Galileo - Aristotelian world view simply reinforces the idea that all objects when given a push will come to rest because coming to rest is the nature of solid objects. This is because solid objects are of the Earth, and the Earth doesn’t move, in the Aristotelian world view. - Galileo observed this exact same thing he came to the exact opposite conclusion - He was not contaminated by expectation or belief in the Aristotelian world view - He realized that an object’s nature being supposedly stationary was pure conjecture (an opinion or conclusion formed on the basis of incomplete information), a belief, and not a fact. - It was the nature of the contact between the object and the surface that caused the object to slow down, not the nature of the object itself. - Galileo was only able to do this because he: (considerations when making scientific observations) - Had a very clear sense of what the relevant and irrelevant phenomena were. - He didn’t overlook anything when carefully observing how objects moved on a surface. - He knew all too well what was based on fact and conjecture in the Aristotelian view of how objects moved, and he certainly made sure his observations were - Not contaminated by expectation or belief. - What did Galileo come to realize was responsible for an object's slowing down then coming to rest? - How significant the contact was between the object and the surface it was on. - What best describes the "extraneous effect" that was obscuring clear-sighted observations of objects moving across a surface after being given an initial push? - The slowing down of the object because of significant contact with the surface. Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 Chapter 2 - Observations What three roles does observation play in scientific inquiry? 1. Observation can enable us to identify and focus in on the relevant facts about the phenomena under investigation. (Passive and empirical observations to develop questions about a phenomenon or process.) a. Passive - gaining knowledge from noticing how something works, without directly affecting the process of outcome b. Empirical - based on observation or experience 2. What we observe can provide clues as to what might explain the phenomena. 3. Observational data can provide the evidence by which we can determine whether various explanations succeed or fail. Why is it crucial to define terms prior to making a set of observations? - Data relevant to these questions cannot be collected until key terms are clarified. - Without a clear sense of how these key terms are being used, subsequent research cannot get off the ground. How does a fact differ from an assumption? Can assumptions be factual? - Fact: something that I know about the phenomena under investigation - Assumptions: what am I assuming based on what I have been told or have heard, read, etc? What role can comparative information play in the process of making a set of observations? - Part of the point of making a set of observations is to determine what, if anything, is unusual about the data collected. What is confirmation bias? - The tendency to selectively focus on evidence that supports our beliefs while rejecting disconfirming evidence is called confirmation bias. What effect can expectation and belief have on observation? - If we suspect, in advance of careful observation, that a claim is true, we may inadvertently overlook data contrary to our belief. What are the defining features of an extraordinary claim? 1. All are highly controversial, in the sense that though there is some evidence for the truth of each, the evidence is sketchy at best. 2. All appear to be at odds with some aspect of our current understanding of the natural world even though the claims generally do not emerge from mainstream science. 3. Advocates of such claims are often unaware of the extent to which their beliefs are in disagreement with established scientific theory. What is an anomaly? Why is the discovery of anomalous phenomena important for science? - An anomaly is something, some state of affairs, that does not square with current, received ways of understanding nature. Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 - Such phenomena can provide a way of testing the limits of our current understanding of how nature works and can suggest new and fruitful areas for scientific investigation. - Anomalous phenomena are important in science because: - their resolution can lead to entire new fields of scientific study. - their resolution can lead to new insights and understanding of nature. - their resolution can lead to new instrumentation or experimental methods to study nature, allowing further new discoveries to take place. - their resolution provides an excellent test of what is generally accepted to be true. - Anomalies are puzzling and unfamiliar and they are potentially revolutionary as well. - Because so much is at stake the investigation of anomalies must be undertaken with two goals in mind. - The first, of course, is to uncover the facts, to get a sense of what is going on. - The second is to determine whether the phenomena can be “explained away.” - It is always a good idea to look for information that has been overlooked by those making the claims. Why do extraordinary claims require extraordinary evidence? - Because so much is at stake, we are entirely justified in demanding extraordinarily decisive evidence for our psychic’s claim to influence objects telekinetically. - If an extraordinary claim were to be true, then some aspect of well-established science would require revision. - Such claims typically fly directly in the face of our current understanding of the world, an understanding obtained from an extraordinarily large body of evidence. - The burden of proof, in other words, lies with the person who claims to have observed something anomalous. - The more extraordinary the anomalous claim—the more extensive the evidence it is false—the more rigorous must be the evidence required before accepting the claim 5 concerns that should be addressed when making careful observations: 1. Do we have a clear sense of what the relevant phenomena are? 2. Have we found a way to insure we have not overlooked anything in the process of making our observations? 3. What do we know for sure? What is based on fact and what on conjecture or assumption? 4. Have we considered any necessary comparative information? 5. Have our observations been contaminated by expectation or belief? In the context of the scientific revolution, discuss the difference between an evidence-based understanding of the natural world versus one based on authority. - They were an authority – meaning that their word could not be argued with, and it was a crime to do so – a crime called heresy - Evidenced-based understanding: A scientist should not simply accept an explanation as true, but should doubt it and try to disprove it through observation and experimentation, i.e., empiricism. Only then, when all possible testing has been conducted, could one hope that the explanation may indeed be true. Without this Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 skepticism then there is no basis, or evidence, that the explanation is correct, we are forced to conclude that there’s no way of knowing if it’s true or not. Discuss the steam engine’s contribution to the industrial revolution and its impact on population growth in industrialized nations. - What actually is the industrial revolution? - Well, it commonly refers to a period of great societal change that took place, first in Britain, Western Europe, followed by the US and Canada and later Japan and other countries as they too industrialized. - It occurred around the late 1700s up until about the early 1800s for Europe and Northern America - Greatest impact on society during the industrial revolution - As an example of just how much more effective the machines were- mechanized cotton spinning, powered by the steam engine increased the output of a worker by a massive factor of 500 - City populations increased rapidly. Average income exhibited unprecedented, sustained growth. The standard of living for the general population increased consistently for the first time in history, and overall there was a massive population explosion - Steam engine power machines to do the work much more effectively and efficiently. - Textiles were the primary products impacted by the revolution in terms of employment, value-added and capital investment - Mechanized cotton spinning - Iron production was also greatly enhanced using the steam engine to power blast air into the furnaces - The demand for coal to power steam engines increased dramatically. Now to get coal, you have to mine it, and Britain had lots of it. - Steam engine powered trains and ships were invented, vastly increasing the efficiency of moving materials around, including food which now was in great demand in the rapidly growing cities - The improvements to agriculture, just prior to the industrial revolution, coupled with new machinery now available to assist in farming and effective means of getting it to where it was needed (steam engine) significantly reduced famine across Western Europe. (not throughout the world) Population predictions - There was a substantial overall drop in the mortality rate of the population. People, on average, survived longer – long enough to have children of their own. So, while the birth rate was high, roughly 6 babies per woman on average across the world, the mortality rate in the industrialized countries decreased markedly. - Mortality is highly predictable and that predicting how many children surviving to become adults is also highly predictable. - How many children there will be born is the hardest part. Why the world population doubled over the course of industrial revolution? 1. The improvements in agriculture allowing more food to be produced. 2. There were improvements in distributing that food, reducing the likelihood of food shortages. Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 3. Improvements in sanitation with sewage systems put in place in cities. - Those nations that underwent a period of social and economic change that transformed the society from essentially agrarian (rural) into one heavily reliant on manufacturing underwent a massive population surge resulting in the world’s total population increasing markedly. - Those nations embracing new technology and mechanization replacing what use to be done by hand far less efficiently were able to reduce their mortality rates considerably during the industrial revolution. - there was another even more incredible population surge just around the corner, in the 20th century. And it’s this surge in world population that truly takes us into the climate crisis and loss of biodiversity at rates usually only associated with extinction level events. Surge in world population that truly takes us into the climate crisis and loss of biodiversity at rates usually only associated with extinction level events. Concept Quiz Science is best characterized by its basic aim: - Science is that activity which aims to further our understanding of why things happen as they do in the natural world by the application of the scientific method. The well-established theories found in our scientific textbooks are the product of the following process: - Rigorous testing and experimentation that eliminates erroneous explanations Why did Prof Bettens feel that the results of the test did not confirm the proposed explanation but only supported it? - We would have to do much more testing in order to check that this explanation is indeed the correct one. How long did the concept of “cadaver matter” run against scientific consensus before the establishment of Germ Theory? - 30 years Who use the scientific method well before the scientific scientific revolution? - Hazan Ibn-Haytham made significant contributions to the principles of optics and visual perceptions. Nicolaus Copernicus’ proposal opposed which accepted idea of that time? - The Sun and other planets rotated about the Earth. But with a Scientific community, individual work can be check, and cross-checked, closely examined by all – accelerating the pace of knowledge acquisition many fold. Good observation necessarily need to be verifiable by other people. Which country’s reliance on coal to fuel their steam engines kickstarted our reliance on fossil Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 fuels? - England What was most emphasized in the video that when coupled with pollution from the incessant coal burning during the Industrial Revolution, worsened the conditions of the newly highly populated cities? - Poor hygiene conditions People - American Physicist, historian, and philosopher of science, Thomas Kuhn (Figure 10) who wrote about scientific revolutions, in general, in his book “The Structure of Scientific Revolutions” - Hazan Ibn-Haytham made significant contributions to the principles of optics and visual perceptions. (use the scientific method well before the scientific scientific revolution) Scientific Revolution 1. Nicolaus Copernicus who, in 1543, published an astronomy book, known in short form as De Rev (Figure 13), on how the planets orbited the Sun and NOT the Earth, and that the Earth itself rotated. This proposal was in direct opposition to the accepted idea that the Earth was the center of the universe, and that everything rotated about the Earth - For 1500 years, an extremely complicated system was devised for the motion of the planets where the Sun and the moon orbited around the Earth. This has been attributed to Ptolemy, a second century astronomer of Alexandria under the rule of the Roman Empire. - Copernicus’s view of how the planets moved replaced the complex Ptolemy system. It’s important to realize that Copernicus’s newer and simpler system wasn’t any better at predicting where the planets would be than the Ptolemy system, mostly because Copernicus believed, as Ptolemy did, that the planets and moon must move in perfect circular orbits with uniform speed. But nonetheless, Copernicus’ proposal was definitely a step in the right direction. - Copernicus just assumed that heavenly bodies must move in perfect circular orbits with uniform speed just like Ptolemy (Do we know for sure what is based on fact and what on conjecture or assumption?) - Copernicus didn’t make many observations. Most of his data was recorded by others and he took them all at face value assuming there were all good and accurate. (Have our observations been contaminated by expectation of beliefs?) 2. Galileo Galilei, who in the late 1500s, early 1600s, studied the motion of objects with experiments to test current explanations of how things moved. He also performed astronomical observations to test Copernicus’ suggestion of a Sun-centered universe instead of an Earth Centered one and to test the Aristotelian view of the heavenly bodies. - It was Galileo’s work in astronomy that really got him into trouble. You see, Galileo built powerful telescopes possessing a magnification of 30 times which was much Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 more powerful than the telescope of that time which only had 3x magnification. - With this telescope he tested the Aristotelian view of the heavenly bodies and a whole bunch of new phenomena could be plainly seen by any who cared to look. - So, with Galileo’s much more powerful telescope than anything that was available at the time he saw a whole bunch of anomalous phenomena: - The sun had sunspots and indicated it was rotating. - The moon was bumpy and cratered looking like there were mountains on it - He saw 4 moons orbiting around Jupiter - He also recorded all the phases of Venus, which was a prediction and a test of a Sun-centered universe. Seeing all the phases of Venus proved it orbited the sun, because in an earth-centered universe you wouldn’t be able to see all the phases of Venus. - All these observations lead Galileo to the realize that the Aristotelian world view must be wrong, and that the Sun, not the Earth, was the center of the universe. 3. Johannes Kepler, who was also working at around the same time as Galileo, proposed an improved model for how the planets moved over Copernicus’ model. Kepler, who had access to some of the most accurate measurements of planet positions during the year, simply could not get the positions of the planets to match with a model like Copernicus’s, where the orbits were perfectly circular executing uniform circular motion. - came up with the idea of the planets orbiting about the Sun in ellipses, rather than circles. Along with his other laws of planetary motion, he produced the most accurate predictions, up until that time anyway, of where all the planets would be at any time of year 4. Francis Bacon articulate the scientific method we have been disucssing in the 1620. Sometimes called the father of empiricism (evidence-based), Bacon convinced the fledgling scientific community that the only way to get to the truth of some explanation was by testing it through observation or experimentation 5. Isaac Newton who integrated the earlier work of Galileo on how objects move and Kepler’s work on how heavenly bodies move, along with the work of others and his own experimentations. - Newton presented his three laws of motion, which were figured out by observations and experimentation on how objects moved on Earth. - He also presented the law of universal gravitation which described how all objects with mass attracted each other. Lecture 2 - The Baloney Toolkit Applied in a Simple Investigation - This toolkit was first created and discussed by the popular science author and scientist Carl Sagan in the last chapter of his book: “The Demon-Haunted World: Science as a Candle in the Dark” 1. Explain the three things you should do before applying the baloney detection toolkit (BDTK). Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 1. Possess a Skeptical Mindset - Any explanation in science is to be given any credibility, it needs to be tested to see if it is false - otherwise it is mere speculation. If we have an explanation that is falsifiable then we have a scientific explanation. - This type of thinking is along the lines of Karl Popper’s philosophy of science, whose ideas we implicitly follow in much of this module. Remember we mentioned Thomas Kuhn in lecture 1, and he disagrees with Popper’s philosophy in certain aspects 2. Be aware of your own biases a. Confirmation Bias - This type of bias refers to the tendency to seek out information that supports something you already believe, and is a particularly pernicious (harmful) subset of cognitive bias—you remember the hits and forget the misses, which is a flaw in human reasoning. People will cue onto things that matter to them, and dismiss the things that don’t, often leading to the “ostrich effect,” where a subject (metaphorically) buries their head in the sand to avoid information that may disprove their original point. i. A cognitive bias is a systematic pattern of deviation from norm or rationality in judgment. Individuals create their own "subjective reality" from their perception of the input. b. Availability Bias - Also known as the availability heuristic, this bias refers to the tendency to use the information we can quickly recall when evaluating a topic or idea—even if this information is not the best representation of the topic or idea. Using this mental shortcut, we deem the information we can most easily recall as valid, and ignore alternative solutions or opinions. - A good approach to overcome availability bias is make decisions after carefully deliberating on the matter, checking and double-checking the sources rigorously, and taking time to examine the evidence. - Another approach to counter availability bias is to make important decisions with a team. - To question the rationale of such decisions, ensuring that all the known evidence (not just the available evidence) have been considered before the decision is made. c. Illusory Truth Bias (a bit like brainwash) - The illusory truth bias (also known as illusion of truth effect, validity effect, truth effect, or the reiteration effect) is the tendency to believe false information to be correct after repeated exposure. When truth is assessed, people rely on whether the information is in line with their understanding or if it feels familiar. The first condition is logical, as people compare new information with what they already know to be true. Repetition makes statements easier to process relative to new, unrepeated statements, leading people to believe that the repeated conclusion is more truthful. 3. Guard your buttons - What is meant by buttons here is: something that sets you off; something that immediately makes you feel, and triggers strong emotions in you. You want to try and Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 make sure your own emotions don’t get the better of you and override your own critical thinking faculties - You should be aware of your feelings, so they don’t cloud your judgment. 2. List the tools in the BDTK and explain how they assist in fact-checking. - The tools from the BDTK were originally developed by Carl Sagan, and have been updated and modified by various people like Michael Shermer over the years What the tools do? Tools used to detect nonsense by helping answer 3 questions: 1. Who is behind the information and why? 2. What is the evidence for the claims? 3. What do other sources say about the source and it's claims? 6 tools in BDTK 1. How reliable is the source of the claim? WHO a. Use LATERAL reading to check on a source (see what other scientists have to say about the work) b. Check the author’s backgrounds, coupled with lateral reading from reliable sources c. Check “about page” d. Perhaps the source is from primary scientific literature (firsthand publication in scientific journals), but even this doesn’t guarantee reliability (some might have questionable peer review process) 2. What is the source's perspective? WHY a. What is their point of view? b. Why was this information shared with you? c. What is the purpose of the information you are looking at? d. Funding of the source - where does the money come from that enables the source to provide you with the information? What you are seeing could be an advertisement to try and sell you something e. Perspectives and biases in literature can colour something, making it seem more or less than what it is. f. Where does the source’s funding come from, and what is their stand? g. Ensure no conflict of interest Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 3. Is the claimant providing positive evidence? WHAT Scientific evidence does NOT include: a. Testimonials, eyewitness account, sworn statements, expert opinions or signed affidavits Scientific evidence include: a. A physical object that can be probed and examined in every detail. b. Repeated measurements made of a mysterious phenomenon, that can sometimes, but not always, be reproduced under what appears to be the same conditions by other scientists. - Evidence must support claims - use lateral reading to establish the credibility of the evidence (see what other reliable sources say about this evidence) - Evidence must be relevant - If evidence is an image, can check a picture with a reverse image search - Images can be altered, taken out of context, not the right date, etc. - Videos can be taken out of context by saying they are about something else, or not show an entire sequence, or can be edited. - Is the evidence POSITIVE? i.e. directly in support of the claim - Presence of evidence is not enough; evidence must be checked to be positive - Evidence must be reliable - Cannot be misrepresented, falsified, fabricated - use lateral reading to establish the credibility of the evidence - E.g. They have just provided evidence that there is something as yet unidentified in the sky, assuming the photo isn’t a fake or the subject of the photo isn’t an artefact of the image which occurred during photo taking. But again, even if you can prove the picture isn’t a fake or artefact, it still isn’t positive evidence of a UFO. You only have evidence that the picture isn’t a fake, the subject isn’t an image artefact, or a weather balloon. That’s all. There can still be many possible explanations for the phenomenon as well as ones we haven’t thought of. Claims need positive evidence Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 to support them, not negative evidence against alternative explanations. Weather - short-term atmospheric conditions Climate - how the atmosphere behaves over relatively long periods of time Steps for reverse image search 1. Copy the URL, or link, to the suspect picture. Typically right-clicking brings up a context menu with one of these as an option. 2. Open a new browser window and go to https://images.google.com/ 3. Click on the camera icon in the search bar ( ), which brings up a “Search by image” dialog box. 4. Select the “Paste image URL” tab, then paste the URL you copied into the search bar. 4. Where does the majority of evidence point? - Well established scientific facts require a significant amount of scientific evidence - So generally, it’s the explanation where the majority of evidence points, is the one that is most often correct. - Anomalies can exist in science; they will have to be put to the test and proven to be true. - A minority stand could end up being false or a fraud. 5. Have the claims been verified by somebody else? - Principle of Reproducibility/replicability is absolutely fundamental to science - Lateral reading and use of face-checking sites would be useful for this section. - Fact-checking sites (www.snope.com) - Irreproducible findings are not considered findings at all in science - Pons and Fleischmann - In 1989 they claimed that they had discovered something called cold fusion. The discovery that Pons and Fleischmann had not actually detected nuclear reaction by-products. 6. Does the claimant use flawed reasoning? - Does what they say actually make sense? Is there a flaw in the logic? - Often when people use numbers to try and present their case, they mask the truth by not properly accounting for an appropriate rate, which actually invalidates their argument. As this BDTK tool says, you need to think about if what the claimant is saying actually makes sense - Is what being said makes sense, or are you just looking at massive numbers presented out of context? Cherry picking - selectively choosing evidence for something and completely ignoring evidence against it (Where does the majority of evidence point - when you cherry pick you ignore the majority of the evidence) Concept quiz Which one of the people below ideas, that we discussed during the Scientific Revolution, are Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 most relevant to the Baloney Detection Toolkit - Francis Bacon (Bacon convinced the fledgling scientific community that the only way to get to the truth of some explanation was by testing it through observation or experimentation) How is examining the human world population relevant to global warming? - Large numbers of people in industrialized nations can pump huge amounts of CO2 into the atmosphere - enough to effect the planet's climate. If there is no evidence for a claim or explanation, does this prove the claim or explanation wrong? - No Which of the tools (1 to 6) most closely aligns with the concern "Have our observations been contaminated by expectation of beliefs?" we mentioned when making careful scientific observations? - What is the source's perspective? You are checking a research journal article and you notice that conclusions of the paper appear to support one of the organizations paying for the research. What should you do? - Consider the quality of the journal, the expertise and affiliations of authors, and check for a statement of no conflict in the paper before deciding what to do. Select from the list two on-line or electronic resources we mentioned that could be used as a reliable source of information? - Wikipedia, OurWorldInData We found that the human world population approximately doubled every BLANK years during the industrial revolution? - 138 When we used the tool, "Where does the majority of evidence point?" we discovered the Prof Rosling was BLANK with his historical population estimates. - a little high Population prediction - How many old people in the future depends on how many adults now and - Mortality depends on age, so it is predictable - How many adults depends on how many children, so it is predictable - Hardest part is how many children in the future Huge population surge after WW2 Lecture 3 - Scientific Explanations and Models Define a scientific explanation - It’s an account of how or why something is the case, but what makes the explanation scientific is that it MUST be testable, or falsifiable. Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 - If the tests failed, then the explanation needed to be revised, or an entirely new one provided. - A scientific explanation for something must be subject to falsification. If there’s no way of demonstrating that the explanation is false through experimentation, or “reality checks”, then the explanation is not scientific What does it mean when we say a scientific explanation "must be testable"? - There has to be the possibility of the explanation being falsified Two basic ways in which a theory differs from a hypothesis - Scientific explanations are frequently associated with two terms - “theory” and “hypothesis”. - Hypothesis: What characterizes a hypothesis is that it is tentative or unproven, that is, it hasn’t yet been subjected to any testing or falsification. They are speculative/hunch. - Usually the first step to discovering something new about nature - Theories: A scientific theory is characterized by the breadth and depth of its explanatory power. Explains a wide range of phenomena. - A theory is a conceptual framework for providing explanations - Contain well tested rules and principles - E.g. Scientific theory: is functioning knowledge, not declarative knowledge - Newton’s three laws of motion and the law of gravitation. These laws constitute a scientific theory. They serve as a “conceptual framework” for providing explanations for how and why a vast number of things move about all around us. - Germ theory explains a vast array of diseases exhibited in not just people, but all kinds of organisms. Again, it represents a conceptual framework for explanations of a vast array of diseases and provides insight into their treatment - Big Bang Theory, Quantum Mechanics, Kinetic Theory of Gases, Vanishing- dimensions theory, Germ Theory, Theory of Evolution - A set of related mathematical equations that when applied correctly reproduce and predict what at first sight appears to be quite different phenomena. - A set of self-consistent and unifying concepts that when applied explains and predicts many apparently disparate observations. - Obsolete theory: Theories that were thought to be correct at the time, but eventually came undone because of new evidence that proved them wrong - E.g. Aristotelian world view - demonic theory - Devils and demons were thought to be the cause of disease - Miasmatic theory – a theory that you could catch a disease from “bad air” or even “night air”, i.e., disease was caused by a gas - even superseded or obsolete theories are still called theories - Novel theory: These are theories that can not only explain phenomena that are already explained by well-established theories, but also explain, or at least hope to, anomalies that the current theory has a hard time supporting. These theories are Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 currently under investigation and being subjected to testing. - well-established theories also have to undergo revision when new evidence is uncovered because science is self-correcting Difference: 1. Scientific theories are more general structures capable of explaining a much wider variety of phenomena than a hypothesis. (proven) Hypothesis haven’t been tested. (unproven) 2. A scientific theory will often contain experimentally well-tested, and therefore, well confirmed rules and principles that reveal underlying explanatory similarities between what might seem to be quite diverse phenomena. Explain the difference between two events being correlated and being related as cause and effect. Causation (cause and effect/casual link): - Providing a causal explanation may allow us to understand why such phenomenon exist, but causal explanations may not be straightforward or simple. Here’s six reasons why: 1. A combination of causes leading to an effect 2. Cause and effect can refer to groups - cause and effect can be about groups rather than individual facts or events. For example, smoking causes lung cancer means that lung cancer occurs more frequently among those who smoke. 3. More than one cause can result in a specific effect - Lung cancer can also be caused by elevated levels of radon – a natural radioactive gas, asbestos exposure and elevated levels of other chemicals like arsenic, beryllium, cadmium, coal and coke fumes, silica and nickel. - It can also be caused genetically, especially if it is present in the family history. 4. An effect might not result from a given cause in every case - For example, although smoking is the leading cause of lung cancer, not all smokers contract lung cancer 5. Causal explanations can be negative - For example, fluoridation of water helps prevent tooth decay, or wearing a mask helps prevent COVID transmission 6. Causal explanations can involve a series of linked causes and effects - Causal explanations can involve a series of linked events, like A causing B which in turn causes C. Terms like proximate and remote are sometimes used to describe the relationship between these causes. Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 - A is a proximate cause of B. Likewise, B is a proximate cause of C. A can be termed as a remote cause of C - What is the difference between a proximate and a remote cause? - A causes B which in turn causes C, A is often referred to as a proximate cause of B and a remote cause of C. Correlation: - Correlation is the degree to which two properties, traits or characteristics move in coordination, or in sync, with one another. Note: - When we identify a cause for an effect, we expect there to be some kind of correlation – positive or negative. - Just because two things are correlated doesn’t mean there is a causal relationship/causal link. (correlation is not cause and effect) - No correlation literally means no relationship, whereas negative correlation means there is a relationship and that is where one property goes up,the other goes down - The bottom line is, for causal relationships, like the fertility rate linked to child mortality rate, you expect there to be a correlation. - BUT, finding a correlation between two properties certainly doesn’t mean they are causally linked in some way Discuss the basic features of the following types of scientific explanations: (a) causal mechanism - A causal mechanism is a linked chain of causes, taking us from the remote cause, through a series of proximate causes, eventually leading to the effect we’re explaining - Example: “Debris from the storm severed power lines, thus causing last night’s power outage.” (b) underlying processes - Redescribe what is observed in terms of more fundamental processes (basic level) - Not something cause something (c) laws - Generalized descriptions of regularities that have been found to occur in nature - What happens if heat is applied to a closed container of a gas? Pressure increases. Why? An important law governing the behavior of gases, discovered by Joseph Gay- Lussac, provides the answer. - Example: “The fuel efficiency of a vehicle is determined in part by size and weight. This is because acceleration is directly proportional to force but inversely proportional to mass. Thus, the larger the object you want to move, the greater the force you need to apply, and so the more energy you need to expend.” - Universal laws - Boyle’s law can be used to explain the behavior of gases Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 (d) function. - Explanation based on the purpose that it serves - Example: “The chest pain and breathing difficulty symptomatic of pneumonia result from an infection of the lung tissue. The tiny air sacs of which the lungs are composed—called alveoli—fill with inflammatory fluid caused by the infection. As a result, the flow of oxygen through the alveolar walls is greatly impaired.” Notes: - There is an interdependence between the different ways of explaining phenomena (e.g. laws + process to explain Boyle’s law is a call to the underlying process of this behavior of molecules and atoms.) - All the explanations are testable (e) causes - To explain one thing or event by reference to another that precedes it. - Examples: “Debris from last night’s windstorm caused the power outage.” “Excessive alcohol consumption can damage the liver.” Explain Occam’s Razor, illustrating its use with an example. - Given competing explanations, any of which would, if true, explain a given puzzle, we should initially opt for the explanation which itself contains the least number of puzzling notions - Choose that explanation which is least complex and/or most plausible - Does the claimant use flawed reasoning? - E.g. Copernicus' explanation of how heavenly bodies move vs Ptolemy’s - Occam’s Razor is named after William of Ockham (Figure 17), an English monk, philosopher, and theologian believed to be born on Ockham in 1285. He has been credited with the Occam’s Razor, a methodological principle, that we still apply today. It can be used to help figure out which explanation is most likely to be correct. Discuss what is a scientific model, the different types and their purpose, and explain the difference between a model and a theory illustrating your explanation with an example. - A scientific model is a cut-down and simplified representation of real-world objects, systems or events. They are idealizations of reality, with the extraneous and hopefully irrelevant parts of reality ignored, or treated very crudely or simply. - Models aren’t just about their ability to explain phenomena. They can also be used to test those explanations, make predictions and projections, and enhance our understanding of nature and even aid in the research of figuring out what is going on. 3 categories of models: 1. Physical models - These are actual physical objects representing some aspect of nature. For example, a globe – a model of planet Earth Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 - But physical models, like all models, can also be used to help analyze and study the real system they are meant to represent. There are many such examples, like architectural models of buildings can help with visualization of internal relationships within the structure or external relationships of the structure to the environment. - To assist in better understanding reality, the physical model can be augmented with instruments to make measurements of what’s happening in and around the model. Such measurements can assist in optimization and the design of equipment or processes. For example, the instruments may measure the external flow of air or water around model buildings, vehicles, people, or hydraulic structures. - Physical models can simulate complex air and water flow to a degree of accuracy that is not possible with other types of models. 2. Mathematical/Computer models - It’s when math can be used to describe nature in some way - When all these equations and data are taken together, they then constitute a mathematical model. To solve such a complicated model the equations will often need to be programmed up on a computer for them to “number crunch” the data with the equations and produce meaningful output. 3. Conceptual models - Conceptual models are cut-down versions of reality with only the parts of interest included. A map is one example. It’s a conceptual representation of real-world physical locations and relevant objects. - Diagrams and figures representing ideas and concepts in science can be thought of as conceptual models - Conceptual models of reality might appear quite similar to real world objects, but they could also be diagrams illustrating processes, even one as abstract as a circuit diagram. All conceptual models depict ideas and concepts within science and can be used to explain phenomena and make predictions in the real world, just as physical and mathematical/computer models can. Prediction VS Projection: - Prediction: - something expected to happen - Projection: - a "what if" prediction - something that is predicted to happen given some condition - Of course, we should never lose sight of the fact that models, being cut-down and simplified representations of reality, can actually leave too much of the real-world out and end up producing the wrong results. However, because science is self- correcting, once such an error is discovered, the ignored effect can then be included in the model to make an improved version. (When new information suggests that old beliefs are false, the old beliefs are replaced by new beliefs.) Model VS theory: Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 - Models can be created from the concepts and principles provided in a theory or a hypothesis. As such, these models are concrete applications of the principles or concepts outlined by the theory or hypothesis. Because of this, the results of these models can actually be used to test a hypothesis. - Models are subordinate to the higher-level theory which just expresses the concepts and principles. - For example, Newton’s statement of the three laws of motion and the law of gravitation can be used to construct a computer model of our entire solar system, i.e., the Sun, planets and all their moons, to predict where the Earth and all of these heavenly bodies will be moving into the future. Concept quiz When a scientific law is explained by re-describing what is observed by discussing how molecules and atoms behave at the microscopic level, which explanatory strategy is being used? - Underlying process It has been found that there is a tendency for people to simply accept sales pitches without any evidence when a magic phase like "according to scientists" is inserted in the pitch. This is explained by something called "anonymous authority". Which of the explanatory strategies below most fits this explanation of people's behavior? - Law A reasonably accurate mathematical/computer model was used in Jan 2021 to figure out what would be the sales price of a 1100 sqft flat at Lakeside if the Singapore Property Index (SPI) were to become 250.0 at some point in the future (SPI in Jan 2021 is 197.3). What term best describes the result of the model? - Projection Latitude is the measurement of distance north or south of the Equator. Longitude is from east to west Lecture 4 - Experimentation and Uncertainty 1. Describe the basic process of experimentally testing a scientific explanation and explain the importance of eliminating false confirmation and rejection from an experimental test. Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 - C: But what if careful observations can’t confirm or reject the explanation? - H: We will need to figure out something that SHOULD happen if the explanation was actually correct. This can sometimes be quite hard and may take a lot of creativity and imagination. - I: The next challenge after having figured out something that should happen if the explanation were true is to devise a set of circumstances in which the predicted outcome should occur. That is, figure out an experiment to perform to check if the thing you predicted to happen happens. This part of science, experimental design, can also be quite difficult. - Remember, all scientific explanations MUST be testable, or falsifiable. If the explanation can’t be falsified, then it’s not a scientific explanation, and a new one needs to be considered. - We can see from this flow chart how science self-corrects. You keep running through the flow chart until something works and only then you will be on your way to learning something new about nature Importance of eliminating false confirmation and rejection from an experimental test 2 issues to be addressed when designing an experiment False confirmation - Suppose the experiment you designed to test the theory is flawed in some way. After performing the experiment, you believe the results of it support the scientific explanation, when, in fact, it doesn’t. This is false confirmation. - This can happen if the result of the experiment can readily be explained by something else. For the experiment to support the explanation, we’ll need to prove that the alternative explanation for the result of the experiment can’t be the case. - E.g. It was the claim that “cold fusion” was real and could essentially be produced by a chemical reaction on a bench. Experiment was flawed, which lead to false confirmation that cold fusion was real. - E.g. Polywater was a hypothesized polymerized form of water. Only ever tiny Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 amounts of polywater could be made, but it was reported to possess a density similar to syrup, a much lower freezing point of -40 0C, and a boiling point of 150 degrees. It was first reported in 1961 by Soviet scientists, but gained a lot of attention in the late 1960s. By 1969, the American public and military were very concerned that the Soviets had a new technology that could be used against them. As this was happening at the height of the cold war, the fear and paranoia surrounding polywater intensified. It was hypothesized that if polywater came into contact with regular water, it could turn all the regular water into it, utterly devastating the country. - We also see the critical importance of a scientific community here. Only when scientists from around the world started seriously working on the problem was the issue finally sorted out – and it took several years to do so. False rejection - falsely rejected your hypothesis - false confirmation and rejection of scientific explanations due to improperly designed experiments is a real concern. We need to carefully think through the experiments when testing scientific hypotheses and theories. - E.g. Recall that the first HDMI cable wasn’t functioning correctly. If I had believed it was working correctly then I would have concluded that either the graphics card or mother board was at fault. I would have falsely rejected the hypothesis that the monitor display on my laptop was at fault. - And if you don’t do it, you can rest assured that when you communicate your results to the scientific community, someone else will. Concept quiz When simple straight-forward observations can't directly test a scientific explanation, how do scientists go about testing the explanation then? - Figure out something that should happen if the explanation were correct In the video, polywater was an example of... - False confirmation What does it mean when we say a scientific explanation "must be testable"? - There has to be the possibility of the explanation being falsified 2. Discuss how contemporary scientific research is conducted and its relationship to testing explanations. Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 1. Observation/question (observation) - It starts with observation/question, the same as our nutshell description of the scientific method. - We observe something puzzling, and we want to find out how or why that something happens or occurs. - The question could be almost anything really, but it involves finding out something in nature we currently don’t understand. 2. Research topic area (observation) - In modern science, you always need to do a “literature search”. For this, you’ll need access to a good library, scientific dat bases on published research and access to scientific journal publications. This is done since it could just be a phenomenon that you don’t know about. Others may be fully aware of it, in which case it isn’t really mystery at all – it was just a mystery to you personally. - But after you’ve considered what these other scientists have done, you might be skeptical of their findings or conclusions, or perhaps they overlooked something, and you’re pretty sure their findings are wrong Maybe you even have your own alternative explanation. - This step falls under the “observation” part of the nutshell version of scientific method. 3. Hypothesis (explanation) - is a speculative or tentative scientific explanation that must be falsifiable and/or testable. - This is the second step in our nutshell version of the scientific method. - Of course, the explanation may not necessarily be a hypothesis, it might actually be a theory that already has some supporting evidence. You would know this because you’ve already done a literature search. - It could be that an explanation has already been provided by other scientists, or perhaps it’s a brand-new phenomenon, so you’re going to have to come up with an explanation yourself, or maybe you just aren’t convinced by the current explanation and can imagine better tests of it. - Whatever the case maybe, there is some sort of testable explanation that you can check to see if it can be supported by evidence, obtained through experiments or observations, or rejected. Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 4. Test with experiment (testing) - first have to figure out something that should happen, or maybe shouldn’t happen, if the explanation were true. We might even have to produce a scientific model to make a prediction of what should happen if true. In which case, based on what we expect to happen if the explanation were true (or perhaps not happen), we can then carefully design an experiment, making sure we avoid false confirmation or rejection, to test our explanation. - Performing experimental tests of scientific explanations is not free. Research funding at universities typically comes from grants either from the government or the private sector. - But even if the research is funded, the research team must still answer for what they have achieved with it - If results are not forthcoming, be it either positive or negative, then the research team may not get funding in the future. It also means that research groups can’t just conduct research on whatever they want once funding is awarded. 5. Analyze data (testing) - This part of the process corresponds to the “testing” step in our nutshell version of the scientific method. - It is mentioned here because sometimes the experiment requires gathering data. - Often the data is measurements from instruments, but it could be survey results, or perhaps, they are fragments of historical documents or artifacts, or maybe even camera footage or images. 6. Report conclusion - This is always a requirement of the funding bodies. - Many journals have several editors who are world experts in particular areas of science. So, when you submit your manuscript to the most suitable editor for your research, you also need to provide several (typically three to five) referees to review your manuscript before it can be published. - If your manuscript makes it past the editor, it is sent for peer review - The peer reviewers then make a recommendation to the editor on what changes you need to make to the manuscript to allow it to be published in the journal. Or they may outright reject the manuscript because the work isn’t exciting enough in their opinion, or its seriously flawed, or there’s something else they take serious exception to. Based on the recommendations of the reviewers, the editor decides whether to reject your manuscript or send it back to you to make the appropriate changes as suggested by the referees. Communicating Scientific Findings in the Primary Literature Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 Which part of the publication process is most crucial for establishing the credibility of the published work? - Effective peer review Concept quiz "Analyze data" is often seen in the steps making up the scientific method on the web. Which part of "observe", "explain", "test" was this placed into in the video? - Test When publishing research in the primary scientific literature, which part of the publication process is most crucial for establishing the credibility of the published work? - Effective peer review Once scientists have obtained funding for research, can they use that funding to perform research on anything requested by the public or media journalists? Select the best option below. - No - funding granted is for research into the topic funding was granted for. 3. Explain the meaning of accuracy, trueness, precision and uncertainty illustrating your explanation with examples. Precision - High precision means tight grouping of darts, many measurements close in value to each other. When we have high precision in our measurements, it’s much easier to figure out what value another measurement would be, or where another dart would land. (uncertainty low) - Spread of reading: uncertainty - So high precision means less randomness in our readings which produces Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 low, or small, uncertainty. Thus, a high precision instrument, when measuring one particular thing, has all of its readings virtually the same. Uncertainty - Uncertainty measures the randomness of the measurements - Uncertainty is a quantitative measure of precision (low precision) - Measurements not close to each other (random) Common definition of accuracy ISO definition of accuracy Common definition of accuracy - Accuracy is how close the average of a large number of measurements is from the true value - Accuracy include systematic error in the common definition, precision does not enter into it, does not reflect random error as it only reflects systemic error, accurate but can also be imprecise (random) - Poor aim is called systematic error in science - Uncertainty measures, and precision describes, only the random errors, not the systematic errors - Large systematic error means low accuracy in the common definition - In the common definition of accuracy, an instrument must possess a low, or small, systematic error. It may have high, or large, random error (high uncertainty) - Using the common definition, an inaccurate instrument can NEVER give you a true result because it always has significant systematic error. ISO definition of accuracy - Main difference is that ISO calls accuracy, trueness - Trueness measures how close the true value is from the average of the measurements - Trueness in the ISO definition was equivalent to accuracy in the common definition - Accuracy increases as we move along the diagonal line - Accuracy means low systematic error and low random error - An accurate instrument is one that is BOTH precise and true at the same time. - An accurate instrument will always give you a result close to the true value, even if it is used to make only one measurement. Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 Concept quiz Uncertainty is a quantitative measure of... - Precision Large systematic error means... - Low accuracy in the common definition 4. Explain the relevance of experimental and control groups and the purpose of randomized controlled double-blind experiments. - Double blinding: eliminates additional bias creeping into the outcome of the experiment from both the experimenter and the subjects. - Blinding the subjects controls for the possibility of suggestibility bias influencing the outcome of the result (tendency to fill in gaps in memory with information from others that may well be incorrect) - Subjects should be blinded because of something called the placebo effect. - Placebo-controlled means the subject is blinded, and observer-blinded means the experimenters are blinded - Randomised controlled: By using random selection, kids entered the experimental and control groups in a completely impartial and totally objective way. The laws of chance guarantee that, with enough subjects, the experimental and control groups resemble each other as closely as possible with respect to any and all variables that might increase or decrease the likelihood of infection regardless of whether all of these variables have even been identified. Concept quiz What type of bias is eliminated by hiding from the subject whether they have been given a placebo or the drug? the tendency to fill in gaps in memory with information from others that may well be incorrect. - Suggestibility 5. Explain the meaning of the following terms (a) margin of error - The margin of error provides us with a range of possible values for the result of our experiment, instead of just one value. We have this range because randomness plays a role in the outcome we observe. - To find margin of error, "confidence level" needs to be specified - For a specific sample size, as the confidence level increases, the margin of error increases - Margin of error is small with large sampe size (b) confidence level - A confidence level tells you how confident you are that the experiment you did is one that contains the true value in the range given by the margin of error - To be more confident of the experiment that contain the true value within its Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 margin of error, we can increase our margin of error so that many of our experiments contains the true value within their confidence interval - If confidence interval is too big, but want to keep your confidence at 95%, take more samples - To reduce the margin of error by half, take 4 times more samples - Toss coin: chance of getting correct = 50% - If a person claim they can tell the outcome, they have to be right more than 50% of the time - If the confidence interval includes 50%, we cannot conclude whether the person can tell the outcome as it can be due to luck Table of sample size - Sample size refers to the sample size per control/experimental group - This table is a guide only because its meant for when the % success is not near 100% or 0% - For example, if your sample size was 50, but you calculated a percentage success of 90%, you couldn’t have a margin of error of ±14% because you would get more than 100% as a possible value for the CI. - The point to note here is that the CI, when we’re away from 50% and getting close to 100% or 0% is smaller than that given in the table and of course it can’t exceed 100%, nor can it be less than 0% (c) statistically significant - When you compare two groups and want to establish a causal link (cause and effect) between something you did or did not do to the experimental group, you need to be quite confident that there is a statistically significant Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 difference between the experimental and control groups. - You do this by noting if there is a lot of overlap in the margins of error in the results at a high confidence level, like 95% or better. - The difference is statistically difference at the 95% confidence interval (below image) - we are certain that administering the Salk vaccine causes a drop in the rates of polio infection because the difference between the control and experimental groups was statistically significant at an extremely high level of confidence. - If there’s a lot of overlap, as we can clearly see here, then it’s quite possible that the difference between the two groups is simply due to luck, and it’s not real. The results of this experiment are inconclusive. We cannot be 95% sure that the difference is real and not just due to chance. - In the above example, the range is from 9% (min) to 37% (max), which is 28% range (37-9) - The overlap range is 29%-17%=12% - I.e. The number of percentage points of overlap of the two CIs is 12%. - To calculate the overlap: 12%/28%=42% > ⅓ - In order to get a more conclusive result, the researchers would need a much larger sample so they can reduce their margins of error. Vaccine efficacy formula: - efficacy is for symptomatic cases not asymptomatic cases (d) effect size. - However, just because something is statistically significant, meaning you’re Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 95% sure there’s a difference or causal link, doesn’t mean that there’s a practical difference. That is, the effect observed, the difference that you measure, might not really be that important - Statistical significance at some confidence level doesn’t necessarily mean that the difference is large, important, or has a big effect. 6. Apply the 3 rules of thumb to decide if a study has established a statistically significant difference between an experimental and control group. (1) if there’s no overlap in the CIs, then the difference is statistically significant at the 95% confidence level. (2) If the overlap is less than one-third of the range covered by the two CIs, than the difference could be statistically significant. But the greater the overlap, the less confident we are that the difference is real. (3) Finally, if the overlap is more than one-third of the range covered by the two CIs, the difference is probably not statistically significant. Sensitivity: true positive Specificity: true negative Concept quiz For a specific sample size, as the confidence level increases, the margin of error... - Increases (not decrease, because is not the sample size that increase) Lecture 5 - The Science of Climate Change Casual model - Deterministic (there is cause and effect) William Kingdon Clifford - "it is wrong always, everywhere, and for anyone, to believe anything upon insufficient evidence. ” William James - "There are, then, cases where a fact cannot come at all unless a preliminary faith exists in its coming. ” Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 1. Describe the historical development of our understanding as to the nature of the atmosphere 1. The first suggestion that the atmosphere might be something other than the single substance as envisioned by the early Greek thinkers, came first from the Italian polymath, Leonardo da Vinci (1452–1519), and then later by the English chemist and physiologist, John Mayow (1641–1679), who both suggested that air is composed of two distinct components: ‘fire-air’that supports combustion and life; and, ‘foul-air’that does not. 2. In around 1630, the Flemish scientist, Jan Baptiste van Helmont (1580–1644), coined the term gasto describe the vapours given off when burning wood. He called these vapours, sylvestre. Today, of course, this gas is known as carbon dioxide. 3. Scottish physician, Joseph Black (1728–1799), who in 1756 proved that the gas discovered by van Helmont is naturally present in the atmosphere, confirming that the atmosphere is not a single substance. - Black's experiments involved heating magnesium carbonate and collecting the carbon dioxide given off, which he called fixed air 4. The first person to suggest that the atmosphere may play a role in the growth of plants was Reverend Stephen Hales. He discovered the mechanism by which carbon returns from the atmosphere to the biosphere. 5. this nourishment of plants is carbon dioxide was finally recognised by the Dutch scientist, Jan Ingenhousz, in 1796. The study of plant respiration and transpiration in Vegetable 2. Discuss the discovery of the greenhouse effect and greenhouse gases - Empedocles of ancient Greece was the first to argue that all matter was composed of the classical elements of water, earth, air and fire. - The first person to establish that the atmosphere plays a role in controlling the climate was a French mathematician, Jean-Baptiste Joseph Fourier. - Also confounded schoolchildren with his mathematical techniques, but also for his development of an analytical theory of heat transfer. - He realised that the Earth itself must radiate (emit (energy, especially light or heat) in the form of rays or waves), although at wavelengths we cannot see. - He called this radiation, radiant heat, what we now call infra-red radiation. - The Earth emits infra-red radiation all the time (So long as an object has a temperature it emits heat.) Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 - Fourier made very precise measurements of this radiant heat, and together with the radiation from the Sun, calculated the Earth’s temperature to be −18°C, way below the some 15°C we observe and certainly not conducive for life as we know it. - Fourier realised that this missing something was the atmosphere. The atmosphere, he surmised, must act as an insulator preventing some of this radiant heat from escaping to space and returning that radiant heat to further warm the Earth’s surface. - This was the first formulation of what we now call the greenhouse effect. The term greenhouse effect first appeared in the work of the Swedish meteorologist, Nils Gustaf Ekholm, in around 1900. (coin the term) Importance of water vapour - The Irish physicist, John Tyndall (1820–1893), is commonly credited with explaining the greenhouse effect, which underpins the science of climate change. - To measure the absorption of radiation by various gases, he had to build his own equipment, the ratio spectrophotometer. This sensitive instrument measured the extent to which infrared radiation was absorbed and emitted by various gases filling its central tube. He quickly realised the importance of water vapour in the absorption of terrestrial radiation. - Tyndall determined that carbon dioxide is 90 times more effective at absorbing infra-red radiation than air. He determined methane as being 403 times more effective. He later determined water vapour to be some 16,000 times more effective at absorbing infra-red radiation than pure air. - Tyndall had discovered in his laboratory that certain gases, including water vapour and carbon dioxide, are opaque to radiant heat. He understood that such gases high in the atmosphere help keep our planet warm by interfering with escaping radiation. - Eunice Foote identified carbon dioxide as a greenhouse gas a few years before Tyndall, and also noted its important in controlling the Earth’s surface temperature. - Eunice Foote first to identify carbon dioxide as greenhouse gas - Water vapor is the atmospheric gas that contribute most to the greenhouse effect Underlying process that explains the greenhouse effect - The greenhouse effect is due to the absorption of terrestrial infra-red radiation by gases in the atmosphere, primarily water vapour and carbon dioxide. 3. Recount the discovery of oxygen and its importance in the emergence of chemistry as a distinct science - Combustion was completely misunderstood by the alchemists and early chemists. It was known that air was needed to sustain combustion and to sustain life. It was also known that when a metal was heated in air it changed and gained weight. - One of the most famous attempts to explain combustion is due to two Germans: an alchemist by the name of Johann Joachim Becher (1635–1682); and, a chemist by the name of Georg Ernst Stahl (1659–1734). They are credited with establishing the phlogiston theory for combustion. - Phlogiston theory stated that all combustible materials were made of two Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 parts. One part, called phlogiston, was given off when a substance containing it was burnt. - The remaining part, the dephlogisticated part, was thought to be the substance’s true form, or calx. If something gave off a lot of heat, it was thought to be rich in phlogiston. Growing plants absorb phlogiston from the air, which is why air does not spontaneously combust and also why plant matter burns as well as it does. This is an early description of a biogeochemical cycle. - Despite the fact that it was known that combustion could only take place in air, air had no role in phlogiston theory. - English scientist, Robert Hooke, the Dutch scientist, Ole Borch, the Russian scientist, Mikhail Lomonosov, and the French scientist, Pierre Bayen, produced oxygen in a variety experiments, but failed to realise that this gas was a chemical element. - The reason for this failure was due to widespread acceptance of the phlogiston theory. → illusory truth bias - Michael Sendivogius (1566–1636), described a substance contained in air which he called cibus vitae or ‘food of life’. In experiments he performed between 1598 and 1604, he recognised that this substance is the same as the gas released when saltpetre is heated. (Saltpetre was the name for the chemical nowadays called potassium nitrate.) - The secretive Dutch engineer and scientist, Cornelis Jacobszoon Drebbe(1572– 1633), performed similar experiments, and possibly after a lesson from Sendivogius himself, purified what he called the “spiritous part of it that makes it fit for respiration”. - A third challenger to the title of discoverer of oxygen is perhaps the Swedish pharmacist, Carl Wilhelm Scheele (1742–1786). He produced oxygen by heating mercury oxide and various nitrates in experiments between 1771 and 1772. Scheele called this gas ‘fire-air’ echoing the nomenclature of da Vinci and Mayow. - The person most frequently associated with the discovery of oxygen is the English theologian, Joseph Priestley (1733–1804). On 1 August 1774, Priestley conducted an experiment in which he focussed sunlight on mercury oxide in a glass tube which liberated a gas he called ‘dephlogisticated air’, because it supported combustion and was totally consumed. - He noted that candles burned brighter in this gas and mice were more active and lived longer breathing this gas. Priestley published his findings in 1775 in a paper entitled An Account of Further Discoveries in Air. In his investigations of how the solubility of carbon dioxide varies with pressure, he discovered carbonation. He called his fizzy drink “windy water”. - The final challenger most frequently given a right to the claim of discoverer of oxygen is the French chemist, Antoine-Laurent Lavoisier. He was responsible for naming this gas ‘oxygen’. He discovered oxygen and was beheaded during the French revolution. - In noting that the weight gained by a substance in combustion is lost by the air, he established the Law of Conservation of Mass upon which all modern chemistry is founded. His theory explained this weight gained that had defied explanation in the phlogiston theory. He is rightly regarded as the Father of Modern Chemistry. He is also responsible for the publication of the first modern chemistry textbook, Traité Élémentaire de Chimie. It is thus that the study of gases such as carbon dioxide and oxygen and the solving of the problem of combustion is linked inextricably to the emergence of chemistry as Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 a distinct and rational science. - The three most frequently credited are Scheele, Priestley and Lavoisier - Scheele was the first to isolate this gas, Priestley was the first to publish, but it was Lavoisier who was first to understand the discovery. - If Occam’s razor is applied to the question of whether Scheele, Priestley, or Lavoisier, or possibly all three, should be credited with the discovery of oxygen, the result is quite clear—none of them; oxygen was discovered and isolated more than a century before their births. Sendivogius isolated oxygen and correctly associated it with that part of the atmosphere required for life. This is sufficient to give priority for the discovery of oxygen to Sendivogius. - Anaximenes is a Greek thinker who postulated that all matter was made of the primordial element air Concept quiz Which discoverer of oxygen was the first to truly understand its importance and role in combustion? - Antoine-Laurent Lavoisier 4. Explain the greenhouse effect by reference to the absorption of radiation by greenhouse gases Calculate greenhouse effect - Swedish geologist, Arvid Högbom (1857–1940), began attempting to quantify the natural sources of emissions of carbon dioxide for the purposes of understanding the global carbon cycle. Högbom found that the estimated carbon production from industrial sources, primarily from the burning of coal, was comparable to the natural sources. - These estimates of Högbom led the Swedish chemist, Svante August Arrhenius (1859–1927), to consider the effect of changing amounts of carbon dioxide in the atmosphere. Arrhenius calculated that a doubling of atmospheric carbon dioxide would raise average global temperatures by 5–6°C using mathematical model. That estimate made in 1896 is not so very different from most modern attempts to calculate the temperature change due to increasing carbon dioxide levels. He thought that it might be beneficial to Earth. The first mathematical model to predict the effect on global temperature of increasing carbon dioxide was due to Svante Arrhenius. This had built upon the conceptual work of Joseph Fourier, and the experimental analysis of John Tyndall and Eunice Foote. - The first to suggest that increasing carbon dioxide levels might be having an observed effect was the English engineer and inventor, Guy Stewart Callendar. Like Arrhenius, though, Callendar thought this warming would be beneficial, delaying a “return of the deadly glaciers”. The Keeling Curve - The most important set of data ever recorded in the history of climate change is the data collected from the Mauna Loa Observatory in Hawaii some 3,000 metres above Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 sea level. Charles Keeling is famous for his measurements of carbon dioxide at the Mauna Loa Observatory in Hawaii In 1958, the American scientist, Charles David Keeling (1928–2005), received funding from the National Science Foundation to collect carbon dioxide samples at this base. By 1961, Keeling produced data showing that carbon dioxide levels were rising steadily in what later became known as the Keeling Curve—a data set that continues to this very day. The data was so concerning that by 1963 the Foundation used Keeling’s research in its warning of rapidly increasing amounts of heat-trapping gases. Restoring the quality of our environment - In 1965, U.S. President Lyndon B. Johnson’s Science Advisory Committee published their landmark report, Restoring the Quality of our Environment. This report warned of the harmful effects of fossil fuel emissions - The committee used the recently available global temperature reconstructions and carbon dioxide data from Keeling to reach their conclusions. They declared the rise in levels of atmospheric carbon dioxide to be the direct result of burning fossil fuel. The committee concluded that human activities were sufficiently large to have significant, global impact—beyond the area the activities took place. Predicting the future of climate change - Following the advent of computer models, the American scientist, James Hansen (1941–), published a study in Science in 1981. The results from this study were subsequently found to accurately predict the 0.6°C temperature rise between 1984 and 2017. - In 1988, the same James Hansen, now Director of the NASA Goddard Institute for Space Studies 61, was called before the U.S. Congress to give testimony. Hansen told the congressional committee that it was 99% certain that the warming trend was not a natural variation but caused by a build-up of carbon dioxide and other artificial gases in the atmosphere. What is the difference between the greenhouse effect and global warming? - Without greenhouse effect, we would all be dead. - The greenhouse effect is the name given to the process that causes the surface to be warmer than it would have been in the absence of an atmosphere. - Global warming is the name given to an expected increase in the magnitude of the greenhouse effect, whereby the surface of the Earth will be inevitably hotter than it is now. Metaphor - A common metaphor for the greenhouse effect is that the atmosphere acts like a blanket. Blankets do not behave in the same way as greenhouse gases though. - Blankets keep us warm because they suppress convection. Heat from your bodies is not able to escape because of the blanket. The atmosphere enables convection. - The metaphor works because more blankets means warmer person; more greenhouse gases means warmer planet. - Unfortunately, there are other emissions to the atmosphere that do not follow this metaphor. If we increased the emissions of sulphate aerosols, say through volcanic eruptions, the planet would cool not warm. This was observed following the eruption Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 of Mount Pinatubo in 1991. - It is ironic that we call the effect by which the Earth is warmed by the presence of gases like water vapour and carbon dioxide in the atmosphere the greenhouse effect. - The reason why is because greenhouses behave in exactly the same way as blankets, the glass inhibits convection and prevents the exchange of air between inside and outside. For which two processes in the atmosphere does the blanket metaphor NOT work? - More sulphate aerosol means cooler Earth surface - The atmosphere enables convection (Sulphate aerosols scatter radiation back to space, thus more aerosol leads to a cooler Earth. Blankets inhibit convection whereas the atmosphere enables convection.) Why is the Earth warmer? - The surface of the Earth is warmer than it would be in the absence of an atmosphere, because it receives energy from two sources: the Sun and the atmosphere. Which two energy sources are most important for warming the Earth’s surface? Sun, atmosphere Which two gases are the most important greenhouse gases in the Earth’s atmosphere? - Carbon dioxide, water vapour Mathematical Model to estimate Earth’s temperature - What do we mean though when we say the Earth is a black body? The Earth is clearly not black. Referring to an object as a black body is a technical description; it means the object absorbs all radiation and, assuming the object is in thermal equilibrium, emits a spectrum of radiation determined by its temperature alone. - The fraction of incoming solar radiation that is reflected is often referred to as the Earth’s albedo, and is denoted by the symbol, A. - When we do this, we find that the temperature of the Earth’s surface is 255 K. This is equivalent to −18°C. The same temperature calculated by Fourier. As noted earlier, this would make the Earth an uninhabitable environment. The planet would be a snowball. - It should be noted that if we were to attempt to measure the Earth’s average temperature from space, this value of −18°C is the temperature that would be measured—it is often referred to as the planet’s effective temperature. 1370 W m⁻² - is the energy per square metre arriving earth every second If Albedo = 0.2: Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 Square root 4 [1370 x (1 - 0.2)/(5.67 x 10^8 x 4] = 264K If we assume the Earth is behaving as a black body, then the energy emitted per unit area is given by the Stefan–Boltzmann law. That is the energy per unit area, also known as the intensity, is equal to the Stefan–Boltzmann constant, σ, times the fourth power of the temperature. 5. Estimate the greenhouse effect using the single-layer atmosphere model. Radiation transmitted by the atmosphere - The first thing to note is that the atmosphere cannot absorb and radiate at all wavelengths and so cannot be treated as a black body. - At visible wavelengths, at around 0.5 microns, the atmosphere is largely transparent, that is it lets radiation in the visible to pass through without being absorbed. - At shorter wavelengths in the ultraviolet, particularly below 0.3 microns, the atmosphere is opaque, that is it absorbs all radiation at these wavelengths. - The reason for this is the presence of oxygen and ozone in the atmosphere. The absorption prevents potentially mutagenic radiation from reaching the biosphere. - At infra-red wavelengths, between 6 and 25 microns, the atmosphere is far more opaque. It should be noted that at some wavelengths in the infra red absorption is not possible, because there are no molecules present in the atmosphere that can absorb such wavelengths—this leads to the presence of so-called atmospheric windows. - Radiation emitted by the Earth’s surface at wavelengths in an atmospheric window will escape unhindered to space. - This discussion of the radiative properties of the Earth’s atmosphere predicts how the atmosphere will interact with the various radiations passing through it. Solar radiation at visible wavelengths will largely pass through the atmosphere unhindered. - This radiation will be absorbed by the Earth’s surface. The Earth's surface will then emit radiation at wavelengths dependent on its temperature, that is in the infra red. - The atmosphere will largely absorb all this terrestrial radiation. The atmosphere will also emit radiation dependent on its temperature, but it will not be able to emit at all wavelengths. - This radiation is emitted in all directions. The component directed towards the Earth’s surface acts as an additional source of energy and results in the elevated Earth surface temperature. Atmosphere model - We noted that the spectral distribution, that is the intensity of radiation emitted by the black body at different wavelengths, is simply determined by its temperature. - Wien’s law describes this relationship; it states that the wavelength of peak of the spectral distribution is inversely proportional to its temperature. - The simplest way to extend our mathematical model to include an atmosphere is to treat the atmosphere as a single layer of uniform temperature. Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 6. F_a → ux from atmosphere - atmosphere radiates energy and does so back to space and back towards the earth surface Incoming F_s → solar ux - Solar flux or concentrated sunlight is a measure of how much light energy is being radiated in a given area - Takes into account of Earth’s albedo T_s → solar transmittance - we need to account for the absorption of radiation by the atmosphere - Hence, transmittance as the fraction of radiation that is not absorbed, hence it reduce the solar flux Leaving as earth emits radiation F_g → terrestrial ux/ground ux - earth’s surface temperature T_g → terrestrial transmittance - reduce the terrestrial flux leaving earth because the earth’s atmosphere absorb radiation - Terrestrial flux that gets through the atmosphere and escape into space Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 - To calculate the terrestrial flux, we need representative values for the solar and terrestrial transmittances. Appropriate estimates are 0.8 for solar transmittance and 0.1 for terrestrial transmittance. These numbers mean that 80% of solar short-wave radiation gets through the atmosphere without being absorbed, but only 10% of terrestrial long-wave radiation gets through the atmosphere without being absorbed. - Terrestrial flux is proportional to the fourth power of the Earth’s surface temperature. - The greater the terrestrial flux, the greater the Earth’s temperature. - According to the single-layer atmosphere model, surface temperature decrease if albedo (proportion of radiation that is reflected) increases - When albedo decrease, solar flux is smaller, this change propagates through the entire earth system resulting in smaller ground flux and ultimately smaller earth surface temperature - If we decrease the transmittance of terrestrial radiation (t_g), for example if we were to increase the amount of greenhouse gases absorbed in the atmosphere, then this expression would lead to an increase in the terrestrial flux (f_g) and thus an increase in the Earth’s surface temperature. - Vice versa, if t_g increase, the earth’s temperate (f_g) decrease because more radiation/ground flux (t_g) is escaped to space - The Earth’s surface is 34 K warmer than it would be without an atmosphere. This is the magnitude of the greenhouse effect. Lecture 6 - Establishing the Scientific Consensus on Climate Change 1. Describe the history of the establishment of the scientific consensus on climate change including the role played by the IPCC - The IPCC is an intergovernmental body of the United Nations mandated to provide objective scientific information relevant to understanding human-induced climate change, its natural, political, and economic impacts and risks, and possible response options. - Published 3 reports. In these assessment reports, the systematic review of the Downloaded by yunhan ([email protected])  lOMoARcPSD|31354065 scientific literature revealed that the scientific consensus was that human-induced climate change through burning fossil fuels was being identified in the observational record. - Intergovernmental Panel on Climate Change, or IPCC, published its Sixth Assessment Report in August 2021. In that report, it is noted that temperatures have risen by more than 1°C since the 1850–1900 global average, and that it is “unequivocal (no doubt) that human influence has warmed the atmosphere, ocean and land”. It describes the ways in which Earth’s climate has changed due to human activity as “unprecedented” (never known before) in the previous hundreds of thousands of years, with some of the changes as now being inevitable and “irreversible". This is the current scientific consensus. IPCC first assessment report (1990) - It published its First Assessment Report in 1990 in which they stated, “global mean surface air temperature has increased by 0.3 to 0.6°C over the last 100 years”. They further noted that “The size of this warming is broadly consistent with predictions of climate models, but it is also of the same magnitude as natural climate variability”. IPCC second assessment report (1995) - However, in their Second Assessment Report published in 1995, the IPCC noted that, “The balance of evidence suggests a discernible human imp