Global Climate Change PDF

Lec_1  GLOBAL CL MATE HANG Upsala Glacier, Argentina, 1928 Upsala Glacier, Argentina, 2004 Weather Climate - short term - averaged over a long period of - ‘present condition’ of the time (~30 yrs) atmosphere...

Lec_1  GLOBAL CL MATE HANG Upsala Glacier, Argentina, 1928 Upsala Glacier, Argentina, 2004 Weather Climate - short term - averaged over a long period of - ‘present condition’ of the time (~30 yrs) atmosphere - how the atmosphere ‘behaves’ - what you get - what you expect - can change within minutes or - long term pattern of weather hours Climate change - long term shift in temperature and weather patter - result of Global Warming - Greenhouse effect and - Greenhouse gases - how much heat is moving around and where it goes - Long term climate change happens over a period of 10s – 100s of millions of years. - Short term climate change takes place over 40 billion tons – CO2 levels are highest in the past 800,000 years. Human Impact on Global Climate: Increasing CO2 levels Human greenhouse gas emissions have steadily increased since the start of the industrial revolution. CO2 in the atmosphere has steadily climbed since the first direct measurements in 1958. The annual oscillation reflects CO2 removal by plants in the northern hemisphere summer. In 1958, CO2 was ~315 ppm; in 2010, it had risen to ~390 ppm. Tutorial  Heat Distribution Lec 2 Physical Properties of Atmosphere n thin gaseous layer surrounding the earth and stratified into layers with abrupt changes in T caused by absorption of incoming solar radiation.  Troposphere – contains 75– 80% earth’s air mass,78% N2, 21% O2, 0.038% CO2, other gases, dust and soot. Contains Clouds and responsible for weather and climate. Stratosphere - similar composition as troposphere except less H2O vapor and much more O3. Ozone layer  Solar Energy Reaching the Earth Electromagnetic radiation - UV radiation (short wavelength – lots of energy per time) - Visible light (most of the energy from the sun that reaches earth surface) - Heat (infrared longer wavelength) Natural greenhouse effect Energy in = energy out Enhanced greenhouse effect Human-enhanced global warming Greenhouse Gases H2O (water vapor) CO2 (carbon dioxide) CH4 (methane) O3 (ozone - tropospheric) Relative contribution of greenhouse gases N2O (nitrous oxide) to the greenhouse effect These gases have always been present in the earth’s troposphere in varying concentrations. Fluctuations in these gases, plus changes in solar output are the major factors causing the changes in tropospheric temperature over the past 400,000 years.  Solar radiation Absorbed Greenhouse by the earth effect  The Natural Greenhouse Effect As Earth’s surface absorbs solar radiation, the surface increases in temperature and emits infrared radiation. Longer wavelength radiation is reflected back to surface. A large portion (34%) of the sun’s radiation is reflected back into space by the atmosphere. What does make it into the atmosphere (66%) is ultimately radiated back into space as heat. Therefore energy in = energy out. Otherwise the Earth would continually warm and life could not exist. Of the incoming radiation reaching the earth, 80% is used to warm the troposphere, and evaporate and cycle water. About 1% generates winds. Photosynthetic organisms use only about 1% (0.1 - 8%) to produce biomass which ultimately moves through trophic chains (webs). The point is that not much incoming radiation actually creates “food energy” and then this is greatly diminished as the “energy” goes up the food chain because of entropy.  Emitted radiation fall within the infrared (IR) part of the spectrum (wavelengths of 4-50 µm) Emissivity – the ratio of actual emission to blackbody emission - between 0 (lowest emission) to 1 (highest emission) Emissivity Land, ocean, surface clouds thicker than 1 the cirrus clouds (thin, wispy clouds) Clear sky atmosphere 0.4 – 0.8 Cirrus clouds 0.2 Land, atmosphere and clouds also ‘absorb’ IR radiation Absorptivity – the ratio of absorbed radiation to incident radiation  Atmosphere absorbs a portion of the radiation stream from the surface and replaces this stream with it’s own emission As long as the atmosphere is colder than the surface, the replacement stream is less than original stream, so that the net emission of IR radiation to space is reduced Therefore, the greenhouse effect depends on two factors: - the difference between surface and atmospheric temperature - the atmospheric emissivity  Although the atmosphere also emits radiation to the surface, this downward emission does not constitute the GHE The trapping of outgoing radiation is far more important to the surface temperature than is the downward IR emission The atmosphere and surface are tightly coupled by heat fluxes Downward emission redistributes heat within the surface and atmosphere without affecting the total amount of heat available Whereas partial trapping of radiation emitted to space alters the heat balance of the combined atmosphere + surface system  Greenhouse Effect Elsewhere? Mars Venus – about the same size as Earth – smaller than Earth - fairly close to the Sun - very thin atmosphere - CO2 and deep clouds of sulfuric acid - CO2 - prevent much of the sunlight from - small but significant GHE reaching the surface - so why not cold? - temp over 500°C - very thick absorbing atmosphere Runaway GHE a planet's atmosphere contains greenhouse gas in an amount sufficient to block thermal radiation from leaving the planet, preventing the planet from cooling and from having liquid water on its surface Venus Early Venus atmosphere - had a lot of water vapor - rise in surface temperature - more evaporation of water – larger GHE - further increase in temperature - process would continue until either atmosphere became saturated with water vapor or all available water had evaporated Runaway GHE on Earth? Earth and Venus – about the same size - similar initial chemical composition No Runaway GHE on Earth Reason – Venus closer to Sun than Earth - amount of solar energy falling on Venus is about twice that falling on Earth - on Venus water on surface would have continuously be boiling - because of high temperature the atmosphere would never have become saturated with water vapor - on Earth – there is equilibrium between the surface and atmosphere saturated with water vapor at different stages  Natural and Enhanced GHE Natural GHE - due to the natural occurrence of greenhouse gases in the atmosphere - because of this the Earth is warm and supports life Enhanced GHE - due to human activities that have led to high concentrations of greenhouse gases in the atmosphere - global warming - climate change  Global Warming Potential - developed to allow comparisons of the global warming impacts of different gases - the ability of greenhouse gases to trap extra heat in the atmosphere over time relative to CO2 - most often calculated over 100 years - GWP depends on two things – how effective the gas is in trapping heat while in the atmosphere - how long it stays in the atmosphere (before it breaks down)  Carbon dioxide equivalent or CO2e - the number of metric tons of CO2 emissions with the same global warming potential as one metric ton of another greenhouse gas - Having a common scale for all greenhouse gases allows comparisons between emissions from different activities or sectors - helps us to decide how much effort should be put into reducing the levels of different greenhouse gases - allows emission-reducing strategies that target different gases while minimizing the economic impact  Heat Distribution and Global Circulations Lec 3  Global Air Circulation Three factors influence how air circulates and thus moves heat and moisture around the planet - Uneven heating of Earth’s surface by the Sun - Rotation of the Earth - Variations in properties of Air, Water, and Land Results in Six cyclical convection cells Milutin Milanković (Milankovitch in English) (1879 – 1958) A Serbian civil engineer and geophysicist, related variations of the Earth’s orbit and long-term climate change, now known as Milankovitch cycles.  Milankovitch cycles 100,000 year cycle 41,000-year cycle 26,000-year cycle Eccentricity determines the Axial tilt determines the Earth spins like a top, so length of the seasons. percentage of the Earth’s the direction our axis Affects amount of radiation to surface that receives direct points changes over time. Earth. sunlight. Precession determines when the seasons occur.  Solar Energy and Global Air Circulation: Distributing Heat Global air circulation is affected by the uneven heating of the earth’s surface by solar energy, seasonal changes in temp and precipitation.  In the far north energy from the Sun is dispersed. In the tropics energy from the Sun is Figure Schematic diagrams showing the voriotions of solar intensify (energy per unit area) with angle of incidence to the Earth's surface. Lower concentrated. angles (higher latitudes) result in the some energy spreod out over a larger area and thus in a lower intensity of radiation.Scene depicted is for Northern Hemisphere winier. © 2009 Pearson Education, Inc. Adapted from Miiier et a l 1983.  Uneven heating of earth’s surface by the sun Same energy spread over greater area = Differential Energy intensities (kcal m-2 sec-1). High latitudes = more heat is lost than is gained from solar radiation. Due to low angles of incidence of solar rays and albedo of ice. Low latitudes = more heat is gained than is lost. Global circulation of the atmosphere and oceans “maintains balance”.  Physical properties of atmosphere Warm air, less dense (rises) Cool air, more dense (sinks) Moist air, less dense (rises) Dry air, more dense (sinks)  Movements in Atmosphere Air (wind) always moves from regions of high pressure to low Cool dense air, higher surface pressure Warm less dense air, lower surface pressure  Energy Transfer by Convection  Movements in Air Non-rotating Earth Air (wind) always moves from regions of high pressure to low Convection or circulation cell Movements in air on a rotating Earth: Coriolis effect Global atmospheric circulation  Global Atmospheric Circulation Circulation cells as air changes density due to: – Changes in air temperature – Changes in water vapor content Circulation cells – Hadley cells (0o to 30o N and S) – Ferrel cells (30o to 60o N and S) – Polar cells (60o to 90o N and S)  Equator Northerlies Sou-westerlies NE Trade Winds + lntert ropical (cold) (warm) convergence zone Global Air Circulation  Global Atmospheric Circulation High pressure zones – Subtropical highs – Polar highs – Clear skies Low pressure zones – Equatorial low – Subpolar lows – Overcast skies with – lots of precipitation  Global Wind Belts Trade winds - Northeast trades in Northern Hemisphere - Southeast trades in Southern Hemisphere Prevailing westerlies Polar easterlies Boundaries between wind belts Doldrums or Intertropical Convergence Zone (ITCZ) Horse latitudes Polar fronts Modifications to idealized 3-cell model of atmospheric circulation More complex in nature due to Seasonal changes Distribution of continents and ocean Differences in heat capacity between continents and ocean - Monsoon winds Actual Pressure Zones and Winds Heat Distribution and Global Circulations: Ocean Circulation Lec 4  Earth’s Surface Features and Climate Heat absorbed and released more slowly by water than by land Large bodies of water moderate climate Movement of moist ocean air across a mountain - Rain and snow on windward side - Rain shadow on leeward side – e.g. Death Valley  Rain Shadow Effect Prevailing winds On the windward side of On the leeward side of pick up moisture a mountain range, air the mountain range, air from an ocean. rises,cools, and releases descends, warms, and moisture. releases little moisture. Fig. 5-7, p. 80 Sea breeze front: Daytime = Land heats up faster than water causing air above land to heat and rise (1 – 3). Cool air from ocean descends to replace it (5&7) causing an onshore breeze and bringing moisture. This air is replaced at higher elevations with air from land (6 &4). Nighttime = opposite. Land cools faster than water so warm air over water rises and is replaced by cooler air from land causing an offshore breeze. www.noaa.gov Fronts and storms – fronts are where different air masses meet and where storms typically develop.  Global Ocean Currents Ocean and atmosphere closely linked Wind driven upper ocean circulation Density driven deep circulation (thermocline circulation) Warm and cold currents created by differences in water density Warm, non-saline: less dense Cold, saline: dense Altered by earth’s rotation and continents Affects regional climates Moves energy around the globe Loop of deep and shallow ocean currents Redistributes heat, mixes ocean waters, and distributes nutrients and oxygen Global Ocean Conveyor Belt Circulation Series of ocean currents Thermohaline currents: result of changes in temperature and salinity 1 m3 water takes roughly 1000 years to complete a full cycle around the world on the belt Global Ocean Conveyor Belt Circulation Importance Moves large volumes of waters Transports heat Regulates climate Distributes nutrients and CO2 Supports aquatic ecosystems Sea Surface Temperature (SST) Measurement The average sea surface temperature is around 20°C. However, the temperature of the ocean can vary greatly depending on location and depth. In February 2024, the average global sea surface temperature (SST) was 21.06°C, which was the highest ever recorded. The average surface air temperature was also at a record high, at 13.54°C. https://svs.gsfc.nasa.gov/3652 Sea Surface Temperature (SST) Measurement primarily through satellite instruments that detect the amount of infrared radiation emitted from the ocean's surface additional data collected from sensors on ships, buoys, and ocean reference stations combined using computer programs to create a comprehensive picture of SST across the globe. the more infrared radiation detected, the warmer the sea surface temperature is  ENSO – El Niño Southern Oscillation Global coupled ocean-atmosphere effect El Niño and La Niña – important temperature fluctuations in east-central tropical Pacific Ocean Driver: Fluctuations in the air pressure difference between Tahiti and Darwin, Australia Associated with floods, droughts and other disturbances Greatest impact on developing countries dependent on fisheries and agriculture  El Niño condition occurs when sea-surface water in the east-central equatorial Pacific becomes warmer than average and east winds blow weaker than normal. It represents the warm phase of the ENSO cycle. The opposite condition is called La Niña. During this phase of ENSO, the water is cooler than average sea- surface temperature and the east winds are stronger. El Niño and La Niña episodes typically occur every 3-5 years. El Niño typically lasts 9-12 months while La Niña typically lasts 1-3 years. What is the importance of El Niño? El Niño has an impact on ocean temperatures, the speed and strength of ocean currents, the health of coastal fisheries, and local weather from Australia to South America and beyond. Why is predicting El Niño and La Niña so important? El Niño and La Niña can make extreme weather events more likely in certain regions. If we can predict El Niño and La Niña, we can predict a greater chance of the associated extreme events.  As of mid-August 2024, the tropical Pacific is in a neutral state for the ENSO. La Niña is expected to emerge in September–November 2024 and persist through the Northern Hemisphere winter 2024–25. The World Meteorological Organization (WMO) predicts a 60% chance of La Niña conditions during July– September 2024, and a 70% chance during August– November 2024. The chance of El Niño redeveloping during this time is negligible.  Annual Total Precipitation.... Annual Precipitation i n Centimeters Data taken from: CRU 0.5 Degree Dataset (Ne w e t al) Atlas of the Biosphere Center for Sustainability and the Global Environment University of Wisconsin - Madison  Water Distribution: Annual Precipitation and Water deficit Regions of the Continental U.S. Tropical cyclones (hurricanes) Large rotating masses of low pressure Strong winds, torrential rain Classified by maximum sustained wind speed  Strom systems: basically the same thing but are given different names depending on where they appear. Hurricanes are tropical storms that form over the North Atlantic Ocean and Northeast Pacific. Cyclones are formed over the South Pacific and Indian Ocean. Typhoons are formed over the Northwest Pacific Ocean. Since the Coriolis force is at a maximum at the poles and a minimum at the equator hurricanes can not form within 5 degrees latitude of the equator. The Coriolis force generates a counterclockwise spin to low pressure in the Northern Hemisphere and a clockwise spin to low pressure in the Southern Hemisphere. https://flatearth.ws/cyclonic-rotation  Radiative Forcings, Feedback Processes, and Climate Sensitivity Lec_5 Radiative forcing It is what happens when the amount of energy that enters the Earth's atmosphere is different from the amount of energy that leaves it a measure of the change in energy balance as a result of a change in a forcing agent (e.g., greenhouse gaseous, aerosol, cloud, and surface albedo) to affect the global energy balance and contribute to climate change used to quantify and compare the external drivers of change to Earth's energy balance unit of measurement W/m2 Energy balance due to natural and anthropogenic activities (IPCC, 2013) Link between greenhouse gases, global warming, and climate change (Singh et al., 2001, Global Climate Change)  Solar radiation: electromagnetic radiation emitted by the sun Solar irradiation: amount of solar radiation obtained per unit area by a given surface Instantaneous radiative forcing: change in net radiation (or energy flux) in the tropopause (before any temperatures are allowed to change) Adjusted radiative forcing: inclusion of any changes/adjustments in the stratospheric temperature Ø because the stratosphere changes rapidly and independently of the surface – troposphere system Effective radiative forcing: inclusion of tropospheric adjustments Ø often related to humidity and clouds, that may exhibit fast adjustments to the radiative forcings Radiative Damping the rate at which the net emission of radiation to space increase an imposed positive radiative forcing on the Earth-atmosphere system (e.g., through the addition of greenhouse gases) represents an energy surplus (more absorbed radiation) resulting in a temperature increase of the surface and lower atmosphere which in turn increase the amount of infrared radiation being emitted to space this would reduce the initial imbalance and eventually a new energy balance will be established, but at a new warmer temperature the more rapidly IR emission to space increases with increasing temperature, the less the temperature must increase in order to restore balance the term ‘damping’ arises because it is the increase in the net emission to space as temperatures warm that limits or dampens the increase in temperature  Climate Feedbacks feedbacks play a major role in transitioning radiative forcing into a change in climate they do this by altering the radiative damping important feedbacks to be considered: - amount and distribution of water vapor - clouds - atmospheric temperature structure - areal extent of ice and snow - vegetation - carbon cycle Amount and Distribution of Water Vapor in a warmer climate the atmospheric concentration of water vapor will increase positive feedback as water vapor is a GHG – amplifies the initial change the percentage increase of water vapor is greater in higher altitudes than at lower altitudes this results in a greater climate warming than if the water vapor amount increases by the same percentage in all altitudes because water vapor is more effective as a GHG at higher altitudes the case where the percentage increase in water vapor is larger at higher altitude is equivalent to increasing the water vapor amount by the same percentage at all altitudes, the distribution of water vapor is upward – this serves as a positive feedback a downward shift in water vapor distribution as the climate warms would serve as a negative feedback  Clouds changes in cloud can serve as a positive or negative feedback on climate clouds have a cooling effect by reflecting sunlight which depends on - the difference between the cloud and surface albedos - amount of incident (or incoming) solar radiation the smaller the underlying albedo and the greater the incident radiation – the greater the increase in the reflection of solar radiation to space due to clouds therefore the cooling effect depends on where and when the clouds occur Clouds clouds have a warming effect by absorbing the IR radiation emitted by the surface and re-emitting a smaller amount of radiation (owing to the fact that the cloud top is colder than the surface) since higher clouds are colder the warming effect of clouds depend on how high they are high clouds tend to have a warming effect on climate, while low clouds have a net cooling effect  Aerosols Small solid or liquid particles - a few molecules to 20 μm. Direct radiative effects due to reflection or absorption of short and long wave radiation. Radiative Forcing: Balance of incoming and outgoing energy. Include: sulfate aerosols, organic aerosols (including fossil fuels), back-carbon aerosols, nitrate aerosols, and mineral dust. Can either cool or warm the Earth. Main particulate sources are natural. Soil dust and sea-salt. Total net radiative forcing due to anthropogenic aerosol production estimated to be -1.2 Wm-2 (cooling). Aerosol Cloud Effects Aerosols have direct radiative effects due to reflection or absorption of radiation. Unperturbed clouds have fewer droplets of larger size at same liquid water content (less effective albedo). Anthropogenic aerosols increase albedo by increasing the number of (smaller) droplets (> cloud condensation nuclei – CCN) results in -0.7 Wm-2. Schematic diagram showing the various radiative mechanisms associated with cloud effects that have been identified as significant in relation to aerosols (modified from Haywood and Boucher, 2000). The small black dots represent aerosol particles; the larger open circles cloud droplets. Straight lines represent the incident and reflected solar radiation, and wavy lines represent terrestrial radiation. The filled white circles indicate cloud droplet number concentration (CDNC). The unperturbed cloud contains larger cloud drops as only natural aerosols are available as cloud condensation nuclei, while the perturbed cloud contains a greater number of smaller cloud drops as both natural and anthropogenic aerosols are available as cloud condensation nuclei (CCN). The vertical grey dashes represent rainfall, and LWC refers to the liquid water content.  Atmospheric Temperature Structure Lapse rate – changes in the rate of decrease of atmospheric temperature with height lapse rate alter the relationship between surface temperate and IR emission to space – thereby having an feedback effect on the climate if the lapse rate decreases as climate warms – the upper troposphere warms faster than the lower, and by more than if the lapse rate were constant this means that the IR emission to space increases faster as the surface temperature increases than for a constant lapse rate – so that less surface temperature warming is required in order to restore radiative balance thus a decrease in lapse rate with warming serves as a negative feedback https://www.apsed.in/post/environmental-lapse-rate-vs-adiabatic-lapse-rate-atmospheric-stability conversely, an increase in lapse rate with warming serves as a positive feedback  Areal extent of Ice and Snow reduction in the area of sea ice and seasonal snow-cover over land as climate warms will reduce the surface reflectivity - tending to produce greater warming – positive feedback however, concurrent changes in cloud cover that could be induced by the change in ice or snow could significantly alter the net feedback Vegetation changes in distribution of different biomes or nature of vegetation within a given biome can lead to changes in the surface reflectivity thus having a feedback effect on climate change compared to urban areas vegetation increases albedo – exerting a cooling effect  Climate Sensitivity describes how much the Earth's surface will warm if the atmospheric CO2 concentration doubles calculated by estimating how much the surface air temperature would change if the amount of carbon dioxide doubled the ratio of the steady-state increase in the global and annual mean surface air temperature to the global and annual mean radiative forcing it is standard practice to include only fast feedback processes (e.g., changes in water vapor) but exclude slow feedback processes (possible induced changes in the concertation on GHGs) in the calculation of climate sensitivity the various fast feedbacks alter the climate sensitivity by altering the radiative forcing CO2 doubling is used a benchmark for comparing the climate sensitivities often quoted as the globally averaged warming once the climate has fully adjusted to an imposed doubling of atmospheric CO2 - generally expected to be between 1.5 – 4.5°C the concept of climate sensitivity is useful only to the extent that it is largely independent of the magnitude, nature and spatial pattern of the radiative forcing, otherwise it would have to recomputed for each and every case of interest ENV213_Cimate Change_Exam 1_Study Guide Exam 1 will cover materials from lecture 1 through 5. The exam will be a combination of multiple-choice questions, true/false, find the missing word and essay questions. You must go through all the lectures, videos and article links to successfully answer multiple choice, true/false and find the missing word questions. Review the quizzes and any assignments. Study the following for the essay type questions. All of these questions are fair game for your exam. I will choose from this list, the quizzes and assignments when preparing essay type questions for the exam. Lec 1 Difference between weather and climate. List the different methods for detecting climate change. Discuss any two. List the natural and human causes of climate change. Lec 2 What is runaway greenhouse effect? Would we experience the runaway greenhouse effect on earth? Explain your response. Define the terms global warming potential and carbon dioxide equivalent. Nitrous oxide has a GPW of 310 – what does it mean? Lec 3 List the factors that are responsible for global air circulation. How is heat distributed in high and low latitudes? Name the different types of global atmospheric air circulation cells. Mention their locations. List the different types of wind belts. What are doldrums? How does the polar front affect weather? Explain the Coriolis effect. The equatorial region and 60° N and S experience more weather events than the 30° N and S regions. What causes these variations and which biomes are found in these regions? Lec 4 Explain the daytime and nighttime sea breeze fronts with a diagram. Which phenomenon is responsible for the formation of ocean gyres? What is the difference between El Niño and La Niña? Why is predicting El Niño important? What is the global ocean conveyor belt? Why is the global ocean conveyor belt important? What are the main characteristics of tropical cyclones? Lec 5 What is radiative forcing and how does it affect Earth's climate? What is radiative damping and how does it stabilize Earth's temperature? How does the ice-albedo feedback contribute to global warming? How do aerosols influence radiative forcing? What is climate sensitivity? Why is it important?