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
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.
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)
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 µ m effective radius)
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 Δ Annual Surface Precipitation Temperature • 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
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
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 atmosphere- ocean 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)
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)
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 +0.2 0 -0.2 +0.4 0 -0.4 Sea Ice extent and concentration is enhanced by the inclusion of sea ice dynamics (SH: moves farther into westerlies)
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 ºC +6º -6º 0 Sea Ice dynamics amplifies the cooling that is induced by the injection of aerosols but warms the central arctic (~2 º C changes)
Engineering of a double CO 2 world w/ sea ice dynamics Change in Annual Average Temperature 2 x CO 2 & aerosols minus control 2 x CO 2 minus control ºC 2 x CO 2 & more aerosols minus control Global Ave Δ T (ºC) Not bad. 2xCO 2 - cnt 2.7 º Regional 2xCO 2 &aerosols temp ºC - cnt 0.8 º changes 2xCO 2 & more aerosols - cnt 0.1 º <2 ºC
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
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
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 Δ T = 0.8ºC) (Global Ave Δ T = 0.3ºC) Difference due to ocean & ice dynamics Switches the sign of the large (~40%) precipitation changes in the central Pacific 2xCO 2 - control % change wrt control
Engineering a 2xCO 2 world: impact of ocean & ice dynamics Difference in Annual Average Surface Temperature due to dynamic ocean feedback • 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) ºC 2xCO 2 - control (slab) • Warming (reduced 6ºC 4 cooling) in the arctic 0 ºC 5ºC -4
Engineering a 2xCO 2 world: impact of ocean & ice dynamics Difference in Seasonal Average Precipitation (%) due to dynamic ocean feedback December - February June-August % 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
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
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).
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
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