HONR 229L: Climate Change: Science, Economics, and Governance

Transcription

1 HONR 229L: Climate Change: Science, Economics, and Governance Discussion #9: Climate Models: Perspective of a Physical Scientist Ross Salawitch & Laura McBride rjs@atmos.umd.edu mcbridel@terpmail.umd.edu Class Web Site: ELMS Page: 2 October

2 HONR 229L: Climate Change: Science, Economics, and Governance Fig 2.3, Salawitch et al., Paris Climate Agreement: Beacon of Hope,

3 HONR 229L: Climate Change: Science, Economics, and Governance AT 8, Q1: The reading states "Climate is the average of weather" and includes a sentence that likely seems preposterous to many: Projecting changes in climate due to changes in greenhouse gases 50 years from now is a very different and much more easily solved problem than forecasting weather patterns just weeks from now. The field of actuarial science can be viewed as being analogous to the field of climate prediction: an actuary studies the life expectancy of large groups of people, allowing insurance companies to thrive financially even though they will likely pay out a benefit of some sort upon the passing of everyone they insure. Some contend that "actuarial science is to trying to predict when a specific person will pass away" as "climate science is to trying to predict the weather next month at a specific location such as College Park". State whether you agree or disagree with this contention, and support your answer with a few sentences. Actuarial science, like climate science, uses models to make predictions. These models are based on averages over large populations, but the variability between individuals is such that there is no way to accurately predict exactly when a specific person will die. Climate science similarly bases predictions on the average of a very large number of data points, allowing scientists to forecast global temperatures fifty years from now more accurately than the exact time it will start raining tomorrow. Though it is possible to make guesses about the coming month's weather based on current weather patterns, this would likely be about as accurate as trying to predict when someone will die based on their health, background, and tendency to make poor decisions (even if these predictions were accurate, they would not be productive toward the ultimate goals of determining global climate changes and making money for insurance companies). As Diamond mentioned in Chapter 14 of Collapse, part of the reason global warming is hard to perceive without analyzing temperature trends over decades and centuries is that the global temperature fluctuates both up and down from year to year, just as weather varies from day to day. By looking at the average of weather over time, it is clear that the climate is on a warming trend. 3

4 HONR 229L: Climate Change: Science, Economics, and Governance AT 8, Q1: The reading states "Climate is the average of weather" and includes a sentence that likely seems preposterous to many: Projecting changes in climate due to changes in greenhouse gases 50 years from now is a very different and much more easily solved problem than forecasting weather patterns just weeks from now. The field of actuarial science can be viewed as being analogous to the field of climate prediction: an actuary studies the life expectancy of large groups of people, allowing insurance companies to thrive financially even though they will likely pay out a benefit of some sort upon the passing of everyone they insure. Some contend that "actuarial science is to trying to predict when a specific person will pass away" as "climate science is to trying to predict the weather next month at a specific location such as College Park". State whether you agree or disagree with this contention, and support your answer with a few sentences. Some people now still live shorter lifespans than people did in the 1800s, and some people in the 1800s lived as long as we do now, but both of these occurrences are relatively rare, and so on average we can say lifespan has increased over time. Similarly, there may be some days, or even years, now that are just as cold as before climate change became an issue, but in looking at trends over decades and centuries we can see that the climate has warmed. As Diamond mentioned in Chapter 14 of Collapse, part of the reason global warming is hard to perceive without analyzing temperature trends over decades and centuries is that the global temperature fluctuates both up and down from year to year, just as weather varies from day to day. By looking at the average of weather over time, it is clear that the climate is on a warming trend. 4

5 HONR 229L: Climate Change: Science, Economics, and Governance AT 8, Q2: State: a) the most important and abundant GHG in the atmosphere b) the most important anthropogenic GHG c) the second most important anthropogenic GHG d) the third most important anthropogenic GHG Answers to b) d) should be based on the magnitude of increase in the RF of climate, between 1750 and 2005 For one anthropogenic GHGs, explain how it is known that the increase in the abundance of this gas, since the start of the industrial revolution, is caused by human activity. a) H 2 O (water vapor) responds to human influence, but only indirectly in that a warmer atmosphere holds more water vapor b) CO 2 (carbon dioxide) c) CH 4 (methane) d) Hmmm could be either N 2 O (nitrous oxide), O 3 (ozone), or CFCs (halocarbons) 5

6 HONR 229L: Climate Change: Science, Economics, and Governance 6

7 Human fingerprint on rising CO 2 Update to Fig 1.7, Salawitch et al., Paris Climate Agreement: Beacon of Hope, The increase in CO 2 abundance since the start of the industrial revolution is caused by human activity. The anthropogenic origin of high atmospheric CO 2 is known by isotopic analysis; carbon-13, a carbon isotope at higher levels in oceans, volcanoes, and geothermal vents than in vegetation, is not abundant in atmospheric carbon dioxide. Since fossil fuels come from vegetation, these low carbon-13 levels indicate that high CO 2 is caused by burning fossil fuels. Finally, the ratio between N 2 and O 2, the two most prevalent gasses in the atmosphere, has begun to widen. This is due to the fact that O 2 is consumed when fossil fuels are burned to create CO 2. The air we breathe is slowly being destroyed. 7

8 Human fingerprint on rising CH 4 Fig 1.9: Salawitch et al., Paris Climate Agreement: Beacon of Hope, Concentrations of CH 4 grew six times faster from than over any other 40-year period in the two millennia before Anthropogenic sources to the atmosphere exceed natural methane sources. CH 4 has significant heat retention per molecule "over a 100-year period, CH4 traps 28 times more heat per mass unit than carbon dioxide and 32 times the effect when accounting for aerosol interactions 8

9 Human fingerprint on rising halocarbons (CFCs) Halocarbons are compounds that have no natural causes and are only found from human activities. During the mid-twentieth century, CFCs were commonly used in refrigeration and spray cans due to its nonreactive and nonflammable properties. However, a rise of the compound could be detected and the loss of ozone in the atmosphere followed, which provided undeniable cause that the halocarbons were indeed increasing due to human interference. Before the Industrial Revolution, only a few halogen gases appeared in nature. After the development of new techniques of chemical synthesis, a spike in CFCs, HFCs, HCFCs, and PFCs occurred over the last 50 years. 9

10 HONR 229L: Climate Change: Science, Economics, and Governance AT 8, Q3: a) As the concentration of GHGs in Earth's atmosphere rises, the surface temperature will rise, causing snow and ice to melt. State whether this melting of snow and ice acts as either a negative feedback, no feedback (null), or positive feedback, in response to the initial perturbation and justify your reply with an explanatory sentence --- b) As the concentration of GHGs in Earth's atmosphere rises, the surface temperature will rise, resulting in larger amounts of water vapor to be present in the global atmosphere. State whether this rise in atmospheric water vapor acts as either a negative, null, or positive feedback and also give the best estimate of the magnitude of this feedback, relative to the greenhouse effect caused by rising CO 2. a. As the surface temperature rises, the snow and ice melts, which causes a "positive" feedback in our environment. "Light-coloured areas of the Earth's surface - mainly snow, ice and deserts - reflect the sunlight." As the snow and ice melts, the amount of light-coloured area will decrease, decreasing the amount of energy that is reflected back at the sun and increasing the amount of energy that is absorbed. As more energy is absorbed, the earth warms, melting more snow and ice, leading to a never ending cycling of warming and melting and warming and melting. b. The rise in atmospheric water vapor acts as a "positive" feedback. "The atmosphere warms due to rising levels of greenhouse gases, its concentration of water vapour increases, further intensifying the greenhouse effect. This in turn causes more warming, which causes an additional increase in water vapour." It is a never ending cycle that continuously causes the greenhouse effect and water vapour to increase and this "feedback may be strong enough to approximately double the increase in the greenhouse effect." 10

11 HONR 229L: Climate Change: Science, Economics, and Governance This figure shows warming at 10 km is larger than warming at the surface supporting notion that the lapse rate feedback is negative Since this level of the atmosphere warms faster than the surface, the atmosphere is able to radiate more easily to space: Negative Feedback Water vapor feedback nearly doubles response to rising CO 2 Lapse rate and water vapor feedback, combined, lead to ~45% enhancement 11

12 HONR 229L: Climate Change: Science, Economics, and Governance Positive or negative feedback, in response to surface warming? 12

13 HONR 229L: Climate Change: Science, Economics, and Governance ENSO factors strongly into today s reading and Thurs reading Global Mean Surface Temperature Anomaly, C (relative to pre-industrial) 13

14 HONR 229L: Climate Change: Science, Economics, and Governance Climate Models: Perspective of a Physical Scientist Jennifer Song 2 October

15 What is an El Niño event? El Niño occurs due to unsusually warm water in the ocean that persist for a year or more Can cause floods and droughts It is very predictable due to the unusual temperature of the ocean Caused forest fires in Asia Lower rainfall in Sahel Africa and is linked to ocean surface temperature 15

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18 Large scale atmospheric flows of the so-called Walker circulation, present at start of the video. Note descending air that is associated with dry conditions over Africa. 18

19 Large scale atmospheric flows of the so-called Walker circulation, present at the end of the video. Note ascending air that is associated with wet conditions over Africa. 19

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21 Most recent ENSO event 21

22 What are the four feedbacks that affect the climate? Water Vapor feedback Cloud radiation feedback Ocean circulation feedback Ice albedo feedback 22

23 Water vapor feedback Higher temperatures would allow more water to evaporate Warmer atmosphere holds more water vapor Water vapor is a greenhouse gas The positive feedback loops would lead to double the amount of global warming 23

24 Cloud-Radiation Feedback Clouds reflect solar radiation back to space on the top Blankets to thermal radiation and prevent loss of heat from the bottom Its effects depend on the height/temp of the clouds Low clouds reflect, and high clouds prevent loss of heat Scientists are unsure of their overall effects 24

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29 Ocean Circulation Feedback What is the latent heat and how does it affect the climate? It takes heat for water to evaporate. And when it condenses in the atmosphere, the heat is released in the atmosphere. Coupled system of the ocean and atmosphere Large heat capacity that can dull the extremes of temperatures Why does the ocean have a large heat capacity? Circulation of heat from the equator to the polar regions The ocean and atmosphere exchange heat, water, and momentum 29

30 Ice albedo feedback Albedo: The light or radiation that is reflected from a surface Ice and snow makes the surface of the Earth bright and thus reflect more light As the ice and snow melts, the dark surfaces are exposed 30

31 How can scientists model the climate correctly? Inclusion of all of the feedbacks Properties of clouds that are simulated Generate cloud at level when moisture is above a level Cloud properties, droplets or ice crystals for reflectivity Effects of aerosols on clouds The cloud feedback is simulated differently in different models In most models, the excess water feeds into more high altitude clouds Model the ocean circulation and coupling to the atmospheric circulation Salinity and density of water Exchange of heat water and momentum between ocean and atmosphere Changes in rainfall can affect salinity and can interfere with the ocean circulation Albedo from ice and snow Growth and decay of sea ice Land ice is considered fixed (although considered by some models, see fig. 5.4) Land moisture through evaporation and precipitation 31

32 Validation of the model Observation of the simulation and the movement of chemical tracers Residuals of tritium after the atomic bomb Thermohaline Circulation Cold water sinks in the north Atlantic Ocean and Antarctica Run for years in comparison to current climate Parameters such as rainfall, surface pressure, and temp are used Predict the effect that a large disturbance on the climate Changing parameters to match historical data Volcanic eruptions from Pinatubo in 1991 Successful simulation of the cold winter in the Middle East and the mild winter in western Europe 32

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35 HONR 229L: Climate Change: Science, Economics, and Governance Climate Models: Perspective of a Physical Scientist Last Word: Ross Salawitch 2 October

36 Thermohaline Circulation 36

37 Thermohaline Circulation 37

38 Simple Climate Model ΔT = λ BB (1 + Feedback) (ΔRF GHGs + ΔRF Aerosols ) where λ BB = 0.3 K / W m 2 ΔRF GHGs = Rise in RF of climate due to all GHGs ΔRF Aerosols = Decline in RF of climate due to human aerosols Feedback = Net Effect of Changes Due to Water, Lapse Rate, Clouds, Surface Reflectivity, Ocean Circulation, etc. Fig 1.4, Salawitch et al., Paris Climate Agreement: Beacon of Hope,

39 Empirical Model of Global Climate (EM-GC) Feedback = 1.69 Key model output parameter #1: Climate Feedback Parameter, λ, units W m 2 C 1 T MDL i = (1+ Feedback) (GHG RF i + Aerosol RF i ) / λ P + C o + C 1 SOD i 6 + C 2 TSI i 1 + C 3 ENSO i 2 + C 4 AMOC i Q OCEAN i / λ P where λ P = 3.2 W m 2 / C Aerosol RF= total RF due to anthropogenic aerosols SOD = Stratospheric optical depth TSI = Total solar irradiance ENSO = El Niño Southern Oscillation AMOC = Atlantic Meridional Overturning Circ. PDO = Pacific Decadal Oscillation Q OCEAN = Ocean heat export = κ (1+ γ) {(GHG RF i-72 ) + (Aerosol RF i-72 )} Aerosol RF 2011 = 1.9 W m 2 Fig 2.4, updated: Salawitch et al., Paris Climate Agreement: Beacon of Hope,

40 Empirical Model of Global Climate (EM-GC) Feedback = 1.03 Key model output parameter #1: Climate Feedback Parameter, λ, units W m 2 C 1 T MDL i = (1+ Feedback) (GHG RF i + Aerosol RF i ) / λ P + C o + C 1 SOD i 6 + C 2 TSI i 1 + C 3 ENSO i 2 + C 4 AMOC i Q OCEAN i / λ P where λ P = 3.2 W m 2 / C Aerosol RF= total RF due to anthropogenic aerosols SOD = Stratospheric optical depth TSI = Total solar irradiance ENSO = El Niño Southern Oscillation AMOC = Atlantic Meridional Overturning Circ. PDO = Pacific Decadal Oscillation Q OCEAN = Ocean heat export = κ (1+ γ) {(GHG RF i-72 ) + (Aerosol RF i-72 )} Aerosol RF 2011 = 1.5 W m 2 Fig 2.4, updated: Salawitch et al., Paris Climate Agreement: Beacon of Hope,

41 Empirical Model of Global Climate (EM-GC) Feedback = 0.49 Key model output parameter #1: Climate Feedback Parameter, λ, units W m 2 C 1 T MDL i = (1+ Feedback) (GHG RF i + Aerosol RF i ) / λ P + C o + C 1 SOD i 6 + C 2 TSI i 1 + C 3 ENSO i 2 + C 4 AMOC i Q OCEAN i / λ P where λ P = 3.2 W m 2 / C Aerosol RF= total RF due to anthropogenic aerosols SOD = Stratospheric optical depth TSI = Total solar irradiance ENSO = El Niño Southern Oscillation AMOC = Atlantic Meridional Overturning Circ. PDO = Pacific Decadal Oscillation Q OCEAN = Ocean heat export = κ (1+ γ) {(GHG RF i-72 ) + (Aerosol RF i-72 )} Aerosol RF 2011 = 0.9 W m 2 Fig 2.4, updated: Salawitch et al., Paris Climate Agreement: Beacon of Hope,

42 Empirical Model of Global Climate (EM-GC) Feedback = 0.21 Key model output parameter #1: Climate Feedback Parameter, λ, units W m 2 C 1 T MDL i = (1+ Feedback) (GHG RF i + Aerosol RF i ) / λ P + C o + C 1 SOD i 6 + C 2 TSI i 1 + C 3 ENSO i 2 + C 4 AMOC i Q OCEAN i / λ P where λ P = 3.2 W m 2 / C Aerosol RF= total RF due to anthropogenic aerosols SOD = Stratospheric optical depth TSI = Total solar irradiance ENSO = El Niño Southern Oscillation AMOC = Atlantic Meridional Overturning Circ. PDO = Pacific Decadal Oscillation Q OCEAN = Ocean heat export = κ (1+ γ) {(GHG RF i-72 ) + (Aerosol RF i-72 )} Aerosol RF 2011 = 0.4 W m 2 Fig 2.4, updated: Salawitch et al., Paris Climate Agreement: Beacon of Hope,

43 Empirical Model of Global Climate (EM-GC) Feedback = 0.09 Key model output parameter #1: Climate Feedback Parameter, λ, units W m 2 C 1 T MDL i = (1+ Feedback) (GHG RF i + Aerosol RF i ) / λ P + C o + C 1 SOD i 6 + C 2 TSI i 1 + C 3 ENSO i 2 + C 4 AMOC i Q OCEAN i / λ P where λ P = 3.2 W m 2 / C Aerosol RF= total RF due to anthropogenic aerosols SOD = Stratospheric optical depth TSI = Total solar irradiance ENSO = El Niño Southern Oscillation AMOC = Atlantic Meridional Overturning Circ. PDO = Pacific Decadal Oscillation Q OCEAN = Ocean heat export = κ (1+ γ) {(GHG RF i-72 ) + (Aerosol RF i-72 )} Aerosol RF 2011 = 0.1 W m 2 Fig 2.4, updated: Salawitch et al., Paris Climate Agreement: Beacon of Hope,

44 Empirical Model of Global Climate (EM-GC) Feedback = 0.09 Key model output parameter #1: Climate Feedback Parameter, λ, units W m 2 C 1 T MDL i = (1+ Feedback) (GHG RF i + Aerosol RF i ) / λ P + C o + C 1 SOD i 6 + C 2 TSI i 1 + C 3 ENSO i 2 + C 4 AMOC i Q OCEAN i / λ P where λ P = 3.2 W m 2 / C Aerosol RF= total RF due to anthropogenic aerosols SOD = Stratospheric optical depth TSI = Total solar irradiance ENSO = El Niño Southern Oscillation AMOC = Atlantic Meridional Overturning Circ. PDO = Pacific Decadal Oscillation Q OCEAN = Ocean heat export = κ (1+ γ) {(GHG RF i-72 ) + (Aerosol RF i-72 )} Aerosol RF 2011 = 0.1 W m 2 Fig 2.4, updated: Salawitch et al., Paris Climate Agreement: Beacon of Hope,

45 Empirical Model of Global Climate (EM-GC) AAWR: Attributable Anthropogenic Warming Rate, 1979 to 2010 Fig 2.13, Salawitch et al., Paris Climate Agreement: Beacon of Hope,

46 Empirical Model of Global Climate (EM-GC) AAWR: Attributable Anthropogenic Warming Rate, 1979 to 2010 Fig 2.13, Salawitch et al., Paris Climate Agreement: Beacon of Hope,