GEL 10 - An Introduction to the Earth System: Interactions & Feedbacks 2024 PDF

**Goals of this lecture:** - Understanding climate change is best done by viewing Earth as a 'single system' composed of components that are interconnected. - ***To introduce the fundamentals of the Earth system** --- the components, the feedbacks, and the concepts of (a) 'forcing' of...

**Goals of this lecture:** - Understanding climate change is best done by viewing Earth as a 'single system' composed of components that are interconnected. - ***To introduce the fundamentals of the Earth system** --- the components, the feedbacks, and the concepts of (a) 'forcing' of climate, (b) thresholds & (c) tipping points. These processes are what control the climate system and how climate change will progress in the future.* - *The idea of co-regulation/evolution of climate and life on Earth through natural feedbacks in the Earth system.* *The Systems Approach* ====================== - The Earth System consists of interconnected physical, chemical, biological components (1) the atmosphere (the thin layer of air encompassing the planet), (2) the hydrosphere (oceans, water on land, glaciers & sea ice), (3) the biosphere (all terrestrial & marine living things including microbes), (4) the lithosphere (soil and rock), and (5) the Anthroposphere (humans and their impact on Earth). - all components in the Earth system are linked by exchange of matter and energy --- so a change in one affects the other components. - Example: water moisture in the atmosphere falls as rain on the soil and plants on land; the plants absorb it or it infiltrates the soil and becomes runoff to rivers and lakes or as groundwater; all if it eventually flows back to the ocean, where it evaporates and ends up as water vapor in the atmosphere. - The Earth system behaves as a single, self-regulating system that in the past has prevented climate change from creating conditions under which life cannot live & that has assured the Earth's recovery from past perturbation of its environment. **Movement of Matter & Energy through the System** - Reservoirs & fluxes: - A reservoir is a place where matter or energy is stored for some period of time within the system. - Movement of material (matter) or energy through the reservoirs is referred to as a **flux**. Since it is referring to 'movement' it is expressed as 'amount per time unit'. A system can be stable (healthy) or it can be unstable (in trouble): - When the inflow = outflow (in balance) then the system is considered at steady state (i.e., equilibrium). This is the ideal state because, when a system is in equilibrium all changes are regulated so that a 'normal' is maintained (e.g., good health or recovery from climate change). - When the inflow does not equal the outflow then the system is unstable (out of equilibrium). This will lead to change (perturbation) to the system (e.g., climate change that amplifies background environmental conditions or a pandemic). - The 5 reservoirs of the **Earth system** are all open to one another & with constant flow of energy and matter among them. - The five reservoirs (sub-systems) are the atmosphere, the hydrosphere, the biosphere, the geosphere, and the anthroposphere. - The Earth system wants to be in the stable (healthy) state of 'equilibrium' - A reservoir can be a sink or a sink for matter or energy: - If the flux rate into a reservoir is \> the flux rate out, the reservoir is said to be a sink. - If the flux rate into a reservoir \< the flux rate out, the reservoir is said to be a source. - Climate change (natural and human-induced) occurs when the balance of matter and energy in the sinks and sources change. - And a reservoir can change from a **sink** to a **source** through time. - For example: The earth system is currently 'out of equilibrium' --- evidence of this is the increasing rate of CO~2~ into the **atmosphere** **reservoir** from human activities is greater than the ability of the ocean and vegetation to absorb it (as a sink). - So CO~2~ is building up in the **atmosphere** **reservoir** (now 423 ppm) and thus this reservoir is acting as a **sink** - But prior to the Great Acceleration, when humans escalated their use of fossil fuels for energy and transportation, the atmosphere was supplying more CO~2~ to the ocean reservoir than it was receiving from other reservoirs so the **atmosphere** **reservoir** was acting as a **source**. **Regulation of the System: Feedbacks** The Earth system is regulated by feedbacks that keep it in or near-equilibrium. - A **feedback** occurs when the effect of 1 action triggers a change in a 2^nd^ action, which in turn, 'feeds back' to trigger a change in the original 1^st^ action. - **Negative feedback** - a change in one component leads to a change in the opposite direction in the linked component (one increases the other decreases), which in turn reduces the change in the 1^st^ (initial) component. - **Positive feedback** - a change in one component leads to a change in the same direction in the linked component, which in turn amplifies the change in the 1^st^ (initial) component. - Feedbacks are typically linked to other feedbacks to form feedback loops **Examples of Feedback Loops in the Earth System That Regulate Climate:** - Negative Feedback Loop \#1: Cloud Effects - Increased emissions of CO~2~ from power plants and automobiles leads to enhanced greenhouse effect and warming. This in turn leads to increased evaporation of water from oceans & lakes- the excess water vapor leads to cloud formation. Low lying clouds reflect much of the Sun's heat energy back to space -- leading to cooling (i.e., the reverse of the initial increase in warming). - Whether the effect of the full set of feedbacks (the feedback loop) reinforces the initial change (positive feedback loop) or restores conditions back to stable and equilibrium conditions (negative feedback loop) depends on how many negative feedbacks are included in the loop. - rules of multiplication apply: - a feedback loop is positive if there are NO negative couplings or an even \# of them - a feedback loop is negative if there are an odd number of negative couplings. - **Positive Feedback Loop \#1 & 2: Ice-albedo Effect** - [Increased Ice growth:] The bright white surface of the glacial ice reflects 60 to 90% of the sunlight that strikes it. Called **albedo effect**. So the atmosphere immediately above a growing (white) ice sheet cools and promotes formation of more ice. More ice in turn reflects more light and leads to more cooling. In this feedback loop --- known as 'ice-albedo' effect --- all changes lead to more ice formation -- essentially the feedback leads to changes that amplify the initial increase in ice amount. - **Albedo** is expressed as a % of the sun's light that is reflected from various surfaces back out to space. - [Decreased Ice growth:] The melting of Arctic sea ice is an amplifying (positive) feedback loop. As the Arctic region warms faster than the remaining Earth surface, the ice melts, more sunlight is absorbed into the dark ocean versus being reflected back to space. This causes further warming and further melting of ice. This positive feedback loop amplifies the initial warming caused by rising levels of greenhouse gases & is the reason that the Arctic is warming at a rate 4 times as fast as the rest of the planet. - *Over time in a positive feedback loop OR amplifying feedback loop, the system as a whole moves away from equilibrium, in one direction or another, towards a more extreme condition.* - *Modern climate change is influenced by several positive feedback loops.* - *Example of a positive feedback loop created by extreme heat waves in China over the past couple of years: drought leads to crippled hydro-electric power use leads to more coal burning leads to more CO~2~ in the atmosphere intensifying the CO~2~-driven global warming.* **Life & the Environment Working Together to Regulate the Earth System** - **Gaia Hypothesis**: the 'mother' of all negative (self-regulating') feedback loops that some scientists argue has made planet Earth capable of having and sustaining life over the past 3.6 billion (possibly even as far back as 4.1 billion) years. - life and the environment work together to form a self-regulating whole. That is, life on earth controls climate and vice versa. - [Example]: Marine phytoplankton (photosynthesizing plants) in oceans give of a gas (Di-methyl-sulfide (DMS)) -- why they do so is uncertain as there is no physiological advantage to this process. - But this gas (DMS) mixes with water vapor and forms sulfate aerosols, which in turn form lots of cloud condensation nuclei. - These produce lots of low-lying clouds -- which are very effective at reflecting the Sun's light (they have high albedo) -- thus cooling the earth's surface. - premeditated manipulation of climate or happenstance??? - planetary regulation of climate emerges out of the natural feedbacks between life and the environment -- no need for 'smart biota' with foresight. **Life in a System Dominated by Positive Feedback Loops** - Many feedbacks in the climate system -- especially in one that is warming -- are positive feedbacks. These positive feedbacks amplify (or reinforce) the initial climate change. - With additional warming, more positive feedbacks come onboard - Once the positive feedbacks interact synergistically they can accelerate the response of the system even if the amount of forcing (e.g., emissions of CO~2~ to the atmosphere) does not change. - As a result climate change is not gradual or easily predictable because it has a level of nonlinearity. - And in systems that are dominated by positive feedbacks, there are **climate or ecological threshold** that can be reached at which point any further change could be permanent --- i.e., it is not possible to return to the original conditions. - There are many thresholds in ecosystems and the climate and many are interconnected. - If a threshold is crossed and there is permanent change (which can happen immediately or it can be after some delay of time) then it is called a **tipping point** ---a 'point of no return'. - This means that the massive anthropogenically driven changes in the Earth system (and its climate) could have unexpected consequences --- that could even be permanent. **TAKE AWAY POINTS** - Most natural systems involve many positive and negative feedback loops all working together to regulate the system. - The Earth's temperature over long-time periods has been maintained due to strong negative feedbacks that involve life and the environment. - Understanding feedback loops in the climate system is fundamental for understanding the impact of climate change on Earth's, how quickly changes will occur, and its ability to recover. - Positive feedback loops, which amplify the initial change, can lead to crossing of thresholds & tipping points that in turn push a system out of equilibrium --- possibly involving permanent change (e.g., loss of sea ice; loss of the Greenland Ice Sheet, extinction of certain species). - Systems adjust to external forcings slowly - studies of past climate change show us that sometimes this 'adjustment' is too slow to prevent extinction(s) of certain life forms. - The geologic record tells us that the Earth has always recovered from past natural climate change... the issue is that the recovery can be slow. - Currently, the Earth's ability to efficiently regulate its temperature is failing due to the very **rapid** **rate** increase of human-induced CO~2~ emissions to the atmosphere and the resulting global warming.