Climate Engineering with Aerosols -- Predictable Consequences?

Transcription

1 Climate Engineering with Aerosols -- Predictable Consequences? David S. Battisti, University of Washington Collaborators: Kelly McCusker, Cecilia Bitz and Phil Rasch Introduction: what is out there? Engineering through sulfate aerosols: new results Why might we try it? The impact of global warming on global food production

2 1. Introduction: what is out there? Govindasamy and Caldiera (2000) Use NCAR s Atmosphere GCM (CCM) coupled to a slab ocean AGCM resolution: L19, T31 Experiments: Control: 280ppm Double CO 2 Engineered world: reduce Solar constant by 1.8% Conclusion: Global and regional temperature and precipitation changes simulated with doubled CO 2 are nearly neutralized by an appropriate reductions in the solar constant.

3 1. Introduction: what is out there? Govindasamy and Caldiera (cont) Δ Annual Surface Temperature Double CO 2 Double CO 2 & -1.8% solar Problems Reducing insolation at the TOA is expensive. More feasible to reduce shortwave within the troposphere (different spatial forcing) Regional cancellation due to enhanced sea ice in engineered world No ocean dynamic feedback or no sea ice dynamics -- both of which greatly affect high latitude climate (Seager et al 2001)

4 1. Introduction: what is out there? Rasch et al (2008) Use NCAR s AGCM coupled to a slab ocean AGCM resolution: L52, 1.9º x 2.5º ; interactive chemistry No ocean current feedbacks; no sea ice dynamics Experiments: Control (circa 1950 boundary conditions: 350ppm of CO 2, etc.) Double CO 2 2Tg of S into stratosphere Double CO 2 plus 2Tg of S into stratosphere Details of SO 2 injections Injected into tropics (10ºN to 10ºS) 2km layer centered at 25km SO 2 oxidized to SO 4 Particles volcanic in size (0.43 µm effective radius)

5 1. Introduction: what is out there? Rasch et al (cont) Results: engineering to a less warm (0.7ºC) planet than doubling CO 2 (2.1ºC) also reduces the regional changes in temperature and precipitation Δ Annual Surface Temperature Δ Annual Precipitation Problems No dynamic ocean feedback -- which greatly affects tropical precipitation patterns. No dynamic ocean feedback and no sea ice dynamics -- both of which greatly affect the high latitude climate

6 1. Introduction: what is out there? Robock et al (2008) Uses GISS ModelE climate model Low resolution atmosphere (L23, 4º x 5º) and ocean (L13, 4º x 5º) Experiments: Control: a 1999 run A 40 yr integration with the A1B emission (starting at 1999) Engineered world: Various injection scenarios of SO2 into the stratosphere Concludes: Aerosols introduced into either the tropics or the northern polar regions have far field climate affects The net effect of engineering by stratospheric aerosols (against the A1B emission scenario) would include reduced rainfall in India and throughout the maritime continent (1.5B people) Problems: Ocean model too crude to represent tropical ocean dynamics Ocean and atmosphere model too crude for ice-edge dynamics

7 2. Engineering through sulfate aerosols: new results Hypotheses 1. Regional changes in temperature and precipitation due to increasing CO 2 and climate engineering (via aerosols or any other process) do not depend critically on tropical atmosphereocean dynamics and the processes that are fundamental for determining sea ice extent 2. There are regions of the world where climate engineering will produce knowable changes in temperature or precipitation that are comparable to those due to a doubling of CO 2 Today: testing (1) and exploring (2)

8 2. Engineering through sulfate aerosols: new results Does sea ice dynamics matter? Model: the same model used in Rasch et al: NCAR s CAM (but T42 2.8º x 2.8º, L26) coupled to a slab ocean Now include sea ice dynamics Experiments: the same as in Rasch et al: Control (circa 1950 boundary conditions: 350ppm of CO 2, etc.) Double CO 2 2Tg of S into stratosphere (forcing prescribed from Rasch et al) Double CO 2 with 2Tg of S into stratosphere (forcing prescribed from Rasch et al) One additional experiment: Double CO 2 with enough aerosol to nearly cancel the global temperature change All experiments run to equilibrium. Results presented for annual and seasonal averages (30 years)

9 The impact of sea ice dynamics Change in Annual Average Sea Ice Concentration 2 Tg of S minus control (350ppm) no ice dynamics with ice dynamics Sea Ice extent and concentration is enhanced by the inclusion of sea ice dynamics (SH: moves farther into westerlies) 0

10 The impact of sea ice dynamics Change in Annual Average Surface Temperature 2 Tg of S minus control (350ppm) no ice dynamics with ice dynamics -6º 0 +6º Sea Ice dynamics amplifies the cooling that is induced by the injection of aerosols but warms the central arctic (~2ºC changes) ºC

11 Engineering of a double CO 2 world w/ sea ice dynamics Change in Annual Average Temperature 2 x CO 2 minus control 2 x CO 2 & aerosols minus control ºC Global Ave ΔT (ºC) 2xCO 2 - cnt 2.7 º 2xCO 2 &aerosols - cnt 0.8 º 2xCO 2 & more aerosols - cnt 0.1 º 2 x CO 2 & more aerosols minus control ºC Not bad. Regional temp changes <2 ºC

12 Engineering of a double CO 2 world w/ sea ice dynamics Change in Annual Average Precipitation (%) 2 x CO 2 minus control 2 x CO 2 & aerosols minus control 2 x CO 2 & more aerosols minus control Not bad, but annual deficits of 15% in some places (e.g., SW US) % change wrt control

13 Engineering a 2xCO 2 world: impact of ocean & ice dynamics Does dynamic ocean feedback matter? Model: the same model, but now add ocean dynamics NCAR s CAM (T42 2.8º x 2.8º, L26), including sea ice dynamics Now include ocean dynamics ( high resolution ) Experiments: as in Rasch et al: Control (circa 1950 boundary conditions: 350ppm of CO 2, etc.) Double CO 2 (ramping) Double CO 2 with aerosols (ramping to 2 Tg S at time of CO 2 doubling) Expect Large differences in the tropical Pacific atmosphere and ocean (and teleconnections there from) Large differences in high latitudes

14 Engineering a 2xCO 2 world: impact of ocean & ice dynamics Change in Annual Average Precipitation 2 x CO 2 & aerosols minus control (slab) 2xCO 2 & aeros minus control (ocn ice dyn) (Global Ave ΔT = 0.8ºC) (Global Ave ΔT = 0.3ºC) 2xCO 2 - control Difference due to ocean & ice dynamics Switches the sign of the large (~40%) precipitation changes in the central Pacific % change wrt control

15 Engineering a 2xCO 2 world: impact of ocean & ice dynamics Difference in Annual Average Surface Temperature due to dynamic ocean feedback 2xCO 2 - control (slab) 6ºC 4 0 ºC ºC Enhanced cooling in the southern hemisphere (amplifies dynamic sea ice response) Enhanced cooling in the N. Atlantic (1/3 reduction in ocean heat flux convergence) Warming (reduced cooling) in the arctic 5ºC -4

16 Engineering a 2xCO 2 world: impact of ocean & ice dynamics Difference in Seasonal Average Precipitation (%) due to dynamic ocean feedback June-August December - February % change wrt control There is an large increase in precipitation in the central Pacific due to the inclusion of ocean dynamics. In winter, these changes affect the northern hemisphere temperature

17 Engineering a 2xCO 2 world: impact of ocean & ice dynamics Difference in December-February Average Temperature due to dynamic ocean feedback ºC The winter temperature differences in Australia, China and northern Canada are likely teleconnected from the tropical Pacific

18 Summary of Lessons Learned Insertion of aerosols into the stratosphere of one climate model Greatly reduces the large-scale, regional climate changes due to a doubling of CO 2 The inclusion of ice and ocean dynamics contributes significantly to the regional climate response: Ice dynamics amplifies the high latitude cooling that results from injecting aerosols into the stratosphere by ~ 1-3ºC Ocean dynamics also amplifies the aerosol-induced cooling throughout the mid and high latitudes in the Southern Hemisphere and in the North Atlantic, but it warms the arctic (3ºC impact). Ocean dynamics greatly shapes the response of the tropical Pacific atmosphere-ocean system to climate engineering, and hence affects the wintertime climate response throughout the northern hemisphere (2ºC impact).

19 Summary of Lessons Learned Hypothesis 1 appears to be false: ice and ocean dynamics may significantly shape the regional temperature (+/-3ºC) and precipitation (10-40%) changes due to engineering against doubling CO 2 Unfortunately, these processes are also on the top of the list of major deficiencies in the climate models: Clouds (Achilles heal of the low cloud solution) Simulations of climatological sea ice and its natural variability (uncertainty in sea ice dynamics, errors in atmosphere & ocean pbl parameterizations, etc.) The tropical Pacific climate: deficiencies in the paramerizations of clouds and ocean and atmosphere PBL physics lead to gross errors in the simulated tropical Pacific climate and the response of the atmosphere and ocean to prescribed forcing

20 Summary of Lessons Learned Insertion of aerosols into the stratosphere of one climate model One model = one projection. What is needed to reduce uncertainty? An effort on a scale similar to the IPCC: A large international R&D effort to simulate the response of the climate system to anticipated engineering solutions (not to mention the R&D on the deployment strategies, etc) An IPCC-like mechanism to articulate and evaluate standardized experiments across model platforms, etc. A large increase in qualified human resources What is the best we will be able to do?

21 Summary Comments Opinion: Assuming perfect deployment, errors in the projection of the regional response to climate engineering against 2xCO 2 will be +/- 2ºC and 20% of annual precipitation (same uncertainty in GH projections) Opinion: There will be unwanted surprises. Coal -> Energy -> Acid rain CFCs -> Many useful applications -> Ozone Hole Lead in Gasoline -> high power engines -> lead poisoning Opinion: Success in quantifying the regional climate responses may necessitate a new international policy framework Who can deploy? Under what condions? Who determines the objectives?.

22 Why would we consider climate engineering solutions? Sea Sea level level rise: rise: for low for low laying laying populated populated areas areas Precipitation/snow pack: pack: in stressed in stressed areas areas Temperature: Temperature: for global for global food food supply supply

23 Projected JJA Average Surface Temperature Change: minus Average of 21 climate models forced by Scenario A1B. Multiply by ~1.2 for A2 and ~0.66 for B1

24 Extreme Heat in Western Europe in 2003: JJA temperature 3.6 C above normal Italy: France: 36% drop in maize yields 30% decrease in maize and fodder production 25% decline in fruit harvests 21% reduction in wheat yields Why? heat stress, increased respiration, reduced grain filling, increased spikelet sterilization, By 2100, years of similar temperature stress on agriculture will be the norm throughout the tropics and subtropics due to the summer average temperature changes. Refs: Battisti and Naylor 2009; UNEP 2007; Easterling 2007; Earth Policy Institute 2006; Eurosurveillence 2005

25 Impacts of Climate Change on Food Security Impacts of increased temperature (only): Reduced yields of wheat, rice, maize and soybeans throughout the tropics/subtropics (equatorward of 35º) Approximately -10% per 1ºC warming Est. reduction of 30-40% by 2100 in India, Africa, Middle East, Central America etc. Reduced nutritional content (especially protein in wheat and rice) Increased disease transmission rates Loss of water stored in snow pack and glaciers (e.g., Sierra, Himalaya) Also reduced duration of river flow

26 Impacts of Climate Change on Food Security Other impacts of climate change on agriculture Decreased precipitation throughout the subtropics Increased carbon dioxide and plants Small (0-10%) yield increase for C3 crops for a doubling of CO 2 Effects on plant pathology (reduced protein content and resilience to disease) Negative effects on soil BGC (fertility/water capacity) Sea level rise: salinization and loss of arable land Changes in pest and pathogens (yet unknown)

27 Where do the Food Insecure live? 960 M people are malnourished today 95% are in the tropics/subtropics The food insecure - depend heavily on agriculture for food and income - live in regions where agriculture will be most stressed by global warming Lobell et al (2008) - live in countries that have the greatest population growth rates Estimates: M more people at risk of hunger by 2080 due to climate change

28 Summary of Lessons Learned Insertion of aerosols into the stratosphere of one climate model Greatly reduces the large-scale, regional climate changes due to a doubling of CO 2 The inclusion of ice and ocean dynamics contributes to the regional climate response in non-trivial ways. Unfortunately, these processes are also are on the top of the list of major deficiencies in the climate models One model = one projection. What is needed to reduce uncertainty? A large international R&D effort to simulate the response of the climate system to anticipated engineering solutions (not to mention the R&D on the deployment strategies, etc) An IPCC-like mechanism to articulate and evaluate standardized experiments across model platforms, etc. A large increase in qualified human resources Success in quantifying the regional climate responses will necessitate a new international policy challenges and framework

29 Impacts of Climate Change on Food Security Increasing temperature over the next 50 years will cause decreases in yield: Wheat Yield in Yaqui Valley, MX Decrease in grain filling Decrease in spikelet fertility Increased water stress Increased respiration Important for all crops, but especially for wheat, rice and soybeans (nb, these are the C3 crops that would otherwise benefit from increased CO 2 ) and maize Jan-Mar Night Temp ( C) Lobell 2007

30 Projections of Growing Season Temperature France Observed JJA Temp ( ) 2003 Projections use 22 climate models (IPCC AR4) forced by A1B Emission scenario. Variability taken from observations

31 Projections of Growing Season Temperature France The Sahel 2003

32 Projections of Growing Season Temperature By the end of the 21st Century it will be much hotter everywhere In most of the tropics/subtropics, the seasonal average temperature will very likely exceed the warmest year on record Battisti and Naylor 2008

33 World Food Facts Average ~2700 cal/person Total Calories from plants: 84% (54% from cereals; rice and wheat are ~1/2) from animals: 16% from fish: 1% 40% of the world s food comes from 17% of cropland that is irrigated Rates of Change Cereal yield increase in Green Revolution (~ ): 2%/year Cereal Demand increasing 2%/year World Cereal Production Peaked in 1975 Soil loss 15Mha/yr (~1% of arable land per year) 1/4 of arable land degraded in past 50 years