I. Feedbacks and coupling between Earth System components Earth system interactions In our 1st class, we recognized the Earth as a system of interacting components (i.e. the solid earth, atmosphere, oceans &amp; ice sheets, and biota). Today we look at the nature of interactions within complex systems. today's goals a focus on interactions a working knowledge of the systems approach to the study of Earth and climate science an ability to recognize and use the concept of feedback (negative and positive) an ability to recognize and use the concept of equilibrium (stable and unstable) an understanding of the relationship between forcing, feedback and equilibrium couplings (1-way interactions) positive coupling something increases (decreases) causing something else to increase (decrease) (+) negative coupling something increases (decreases) causing something else to decrease (increase) (-) source: Kump et al. &quot;<a href="/keyword/the-earth-system/" >the earth system</a> &quot; couplings (1-way interactions) negative coupling something increases (decreases) causing something else to decrease (increase) (-) source: Kump et al. &quot;<a href="/keyword/the-earth-system/" >the earth system</a> &quot; feedbacks (interaction in both directions) ? ? more complicated, but more interesting some simple examples.......... negative feedback (w/ simple Hi/Low thermostat) net body temperature based on simple RULE: what happened? feedback = sign of sum of signs of couplings equilibrium temp. no longer changes (much) negative feedbacks are stabilizing time source: Kump et al. &quot;<a href="/keyword/the-earth-system/" >the earth system</a> &quot; negative feedback (w/ simple Hi/Low thermostat) net body temperature what happened? the system has reached equilibrium temp. no longer changes (much) negative feedbacks are stabilizing time (thermostats in the wrong hands) net interactions: 2 positive &amp; 2 negative couplings positive feedback body temperature Jimmy's thermostat the positive is controlling Rosalynn's blanketfeedback and visa versa is destabilizing what happens? time source: Kump et al. &quot;<a href="/keyword/the-earth-system/" >the earth system</a> &quot; what happened? C (thermostats in the wrong hands) net positive feedback (indiv. scales offset) what happened? body temperature the positive feedback is destabilizing (the system is changing at an ever increasing rate) C time positive feedback increases the strength of the influence negative feedback decreases the strength of the influence thus, as we have seen: positive feedbacks are destabilizing negative feedbacks are stabilizing some examples ....... clicker question #1 7 population size (billions) 6 5 4 3 2 1 world population 7 6 5 4 3 2 1 0 0 1750 1800 1850 1900 year AD 1950 2000 is the feedback in this system: a) positive, b) negative, c) restoring equilibrium, d) destabilizing, e) both a &amp; d. discussion: 7 population size (billions) 6 5 4 3 2 1 0 1750 time to reach last billion: yr AD yrs 1927 123 1960 33 1974 14 1987 13 1999 12 7 6 5 4 3 2 1 0 1800 1850 1900 year AD 1950 2000 the system is increasing at an ever increasing rate when did the system really take off? Extent (millions of square kilometers) iClicker question: September sea ice extent Having to guess, is the feedback in this system likely to be a) negative, b) destabilizing, c) positive, d) stabilizing, e) both b &amp; c source: CU-NSIDC What is the feedback process depicted here ? Think about this: sea ice is bright and reflects ~90% of the suns rays, sea water is dark and absorbs ~90% of the suns rays. source: A. Gore's &quot;AIT&quot; pos. feedback involving sea ice sea ice cover temperature &quot;reflectivity&quot; note the sum of all couplings is positive pos. feedback involving global snow and ice cover global temperature global &quot;reflectivity&quot; this can &quot;jump start&quot; an Ice Age after: Kump et al. &quot;<a href="/keyword/the-earth-system/" >the earth system</a> &quot; snow &amp; ice cover example: Scandinavia inception of continental glaciation in plateau areas when conditions permitted snow to linger year `round types of equilibrium consider a ball in a valley now....., on a peak narrower &amp; steeper, less stable and that the ball represents the state of some variable (say temperature) what happens to the ball when dis(per)turbed in this imaginary situation? UNSTABLE (e.g. temperature changes continuously) result of positive feedback teaching slide from Prof. D. Noone (ATOC) types of equilibrium consider a ball in a valley now....., on a peak narrower &amp; steeper, less stable it's STABLE UNSTABLE (if perturbed it tends to (e.g. temperature changes return to equilibrium as continuously) result of negative feedbacks) result of positive feedback teaching slide from Prof. D. Noone (ATOC) types of equilibrium steeper &amp; deeper, more stable consider a ball, now..................., on a peak STABLE (.e.g. temperature returns to equilibrium) result of negative feedback what happens to the ball when dis(per)turbed in this imaginary situation? types of equilibrium steeper &amp; deeper, more stable consider a ball, now..................., on a peak STABLE it's UNSTABLE (.e.g. temperature returns (if perturbed it will tend to to equilibrium) change continuously, as result of negative feedback result of positive feedbacks) types of equilibrium STABLE EQUILIBRIUM (resistant to change as result of negative feedbacks) UNSTABLE EQUILIBRIUM (sensitive to change resulting from positive feedbacks) forcing simple forcing w/ negative feedback feedback I always push (force) the ball up hill What determines the height? forcing How hard I push (i.e. strength of forcing) and how hard the ball pushes back (i.e. strength of negative feedback) examples........ negative feedback in body temp. (warm blooded animals require near-constant internal temp.) skin temperature core temperature brain says shiver short swin - small shock or perturbation &quot;Man Overboard!&quot; - big, long short perturbation what happens if we take ashock orcold swim? body temperature stable to small perturbations, but perhaps not to large or long ones for body temperature feedback note: a sustained perturbation is a forcing forcing or perturbation (what is the difference?) ALIVE stability diagram what might happen if we stay in too long (or worse, Man Overboard!)? stable equilibria DEAD hi temperature low for body temperature stability diagram ALIVE stable equilibria DEAD hi temperature low clicker question: Y X Z what is the relative rank of stability for positions on the diagram from most to least: a) X, Y, Z b) Z, Y, X c) Z, X, Y d) Y, X, Z e) they are all the same for body temperature stability diagram threshold ALIVE stable equilibria DEAD hi temperature low negative feedback in body temp. (warm blooded animals require near-constant internal temp.) skin temperature core temperature brain says shiver short swin - small shock or perturbation &quot;Man Overboard!&quot; - big, long shock or perturbation body temperature stable to small perturbations, but perhaps not to large or long ones so..... negative feedbacks are stabilizing this helps maintain stability in <a href="/keyword/the-earth-system/" >the earth system</a> , to an extent, but..... thresholds exist and can be exceeded what then? What about a longer, more complicated record? CU-INSTAAR's Trevor Popp (HPD) at Summit, Greenland As geologists we have a wealth of climate information from ice cores. Let's take a look. natural CO2 variations 300 280 260 240 220 200 180 0 50 100 150 200 250 300 thousands of years BP 350 Vostok, Antarctica 300 280 260 240 220 200 180 400 number of CO2 molecules for every million molecules of air in Antarctic ice time moves forward from R to L in thousands of years CO ppm 2 clicker question (discuss w/ your neighbors) 300 280 260 240 220 200 180 0 50 100 150 200 250 300 thousands of years BP 350 Vostok, Antarctica 300 280 260 240 220 200 180 400 CO ppm 2 Is the overall feedback in this system: a) positive, b) negative, c) stabilizing, d) both b &amp; c, e) there is no feedback discussion: 300 280 260 240 220 200 180 0 50 100 150 200 250 300 thousands of years BP 350 Vostok, Antarctica 300 280 260 240 220 200 180 400 does the system ever get too far out of whack? CO ppm 2 300 280 260 240 220 200 180 0 50 100 150 200 250 300 thousands of years BP 350 300 280 260 240 220 200 180 400 CO ppm 2 does the system have bounds? a middle? Ice Age CO2 and temperature 4 300 280 260 240 -4 -6 -8 220 200 180 400 temperature change ( C) 2 0 -2 CO (ppm) 2 -10 0 50 100 150 200 250 300 thousands of years BP 350 temperature change curve is blue and it's scale is on the left, what is this graph telling us about temperature and CO2? Ice Age CO2 and temperature 4 300 280 260 240 -4 -6 -8 220 200 180 400 temperature change ( C) 2 0 -2 CO (ppm) 2 -10 0 50 100 150 200 250 300 thousands of years BP 350 temperature and CO2 co-vary (change together) when it gets too cold, CO2 and temperature snap back Ice Age CO2 and temperature 4 300 280 260 240 -4 -6 -8 220 200 180 400 temperature change ( C) 2 0 -2 CO (ppm) 2 -10 0 50 100 150 200 250 300 thousands of years BP 350 notice the system tends to recover from the small nudges when it is already cold, but not when it is already warm stability diagram for Ice Age temperature and CO2 WARM Hi CO2 threshold COLD Low CO2 the diagram illustrates that the system can recover from the nudge on the left, but the same size nudge given on the right would lead to a rapid change stability diagram for Ice Age temperature and CO2 deeper, more stable WARM Hi CO2 threshold COLD Low CO2 i.e. system spends less time in WARM, Hi CO2 state than in COLD, Low CO2 state, and even less time in between recent CO2 variations Charles David Keeling Scripps ~1.5 ppm/yr what is this graph telling us? CO2 in the past and present 400 350 400 recent ice core 350 300 250 200 150 400 CO (ppm) 300 250 200 150 0 50 2 100 150 200 250 300 thoudands of years BP 350 what can we say about recent trends compared to past variations? CO2 in the past and present 400 350 400 recent ice core 350 300 250 200 150 400 CO (ppm) 300 250 200 150 0 50 2 100 150 200 250 300 thoudands of years BP 350 the system is no longer bounded at natural limits population and economic growth have changed the rules what will happen? which way will feedbacks push the system? remember: we need to try to understand the feedbacks in <a href="/keyword/the-earth-system/" >the earth system</a> in order to assess future outcomes next lecture we begin the study of Earth's energy budget with Radiation Reading: Ch. 2 other resources: Kump, Casting &amp; Crane, &quot;<a href="/keyword/the-earth-system/" >the earth system</a> &quot; Pearson Prentice Hall (2004), Ch. 2. must-know terms positive coupling negative coupling positive feedback negative feedback stable equilibrium unstable equilibrium forcing perturbation carbon dioxide key concepts the Earth is a system of dynamic linkages between parts, each part affecting the others negative feedbacks decrease the strength of interaction between components and promote stable, equilibrium conditions (i.e. the state no longer changes, much....) positive feedbacks increase the strength of interaction between components and are generally destabilizing learning objectives Know the difference between negative and positive feedback and be able to use the concept of feedback to predict what will happen to a system if the strength of a variable changes. Explain how a system of only positive feedback works and contrast with a negative feedback system. Describe the difference between stable and unstable equilibrium. Explain the association between feedback (negative and positive) and equilibrium (stable and unstable) Describe a system's response to forcing in terms of feedback and state of equilibrium. Explain how feedback loops can either diminish or increase the effects of forcing (disturbances). Thanks to Jennifer Stempien, SEI