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Can a reduction of solar irradiance counteract CO2-induced climate change? – Results from four Earth system models

Author(s): Schmidt H, Alterskjær K, Karam DB, Boucher O, Jones A, Kristjansson JE, Niemeier U, Schulz M, Aaheim A, Benduhn F, Lawrence MG, Timmreck C

Published: March, 2012

Publisher: Earth System Dynamics Discussions

DOI: 10.5194/esdd-3-31-2012

Tags: Stratospheric Aerosols, Cloud Brightening, Climate Modelling

URL: http://www.earth-syst-dynam-discuss.net/3/31/2012/esdd-3-31-2012.html

Abstract: In this study we compare the response of four state-of-the-art Earth system models to climate engineering under scenario G1 of the GeoMIP and IMPLICC model intercomparison projects. In G1, the radiative forcing from an instantaneous quadrupling of the CO2 concentration, starting from the preindustrial level, is balanced by a reduction of the solar constant. Model responses to the two counteracting forcings in G1 are compared to the preindustrial climate in terms of global means and regional patterns and their robustness. While the global mean surface air temperature in G1 remains almost unchanged, the meridional temperature gradient is reduced in all models compared to the control simulation. Another robust response is the global reduction of precipitation with strong effects in particular over North and South America and northern Eurasia. It is shown that this reduction is only partly compensated by a reduction in evaporation so that large continental regions are drier in the engineered climate. In comparison to the climate response to a quadrupling of CO2 alone the temperature responses are small in experiment G1. Precipitation responses are, however, of comparable magnitude but in many regions of opposite sign.


Solar irradiance reduction to counteract radiative forcing from a quadrupling of CO2: climate responses simulated by four earth system models

Author(s): Schmidt H, Alterskjær K, Bou Karam D, Boucher O, Jones A, Kristjánsson JE, Niemeier U, Schulz M, Aaheim A, Benduhn F, Lawrence M, Timmreck C

Published: January, 2012

Publisher: Earth System Dynamics

DOI: 10.5194/esd-3-63-2012

Tags: Space Reflectors, Stratospheric Aerosols, Cloud Brightening, Climate Modelling

URL: http://www.earth-syst-dynam.net/3/63/2012/esd-3-63-2012.html

Abstract: In this study we compare the response of four state-of-the-art Earth system models to climate engineering under scenario G1 of two model intercomparison projects: GeoMIP (Geoengineering Model Intercomparison Project) and IMPLICC (EU project "Implications and risks of engineering solar radiation to limit climate change"). In G1, the radiative forcing from an instantaneous quadrupling of the CO2 concentration, starting from the preindustrial level, is balanced by a reduction of the solar constant. Model responses to the two counteracting forcings in G1 are compared to the preindustrial climate in terms of global means and regional patterns and their robustness. While the global mean surface air temperature in G1 remains almost unchanged compared to the control simulation, the meridional temperature gradient is reduced in all models. Another robust response is the global reduction of precipitation with strong effects in particular over North and South America and northern Eurasia. In comparison to the climate response to a quadrupling of CO2 alone, the temperature responses are small in experiment G1. Precipitation responses are, however, in many regions of comparable magnitude but globally of opposite sign.


A comparison of the climate impacts of geoengineering by stratospheric SO2 injection and by brightening of marine stratocumulus cloud

Author(s): Jones A, Haywood J, Boucher O

Published: September, 2010

Publisher: Atmospheric Science Letters

DOI: 10.1002/asl.291

Tags: Cloud Brightening, Stratospheric Aerosols, Climate Modelling, Cloud Physics

URL: http://onlinelibrary.wiley.com/doi/10.1002/asl.291/abstract

Abstract: We examine the climate impact of geoengineering via two different methods, namely, stratospheric SO2 injection and increasing reflectivity of marine stratocumulus clouds. Although both methods appear capable, in principle, of counteracting the global mean warming due to increases in greenhouse gas concentrations, significant changes in regional climate still result. The extent of this regional climate change appears linked to the location and degree of inhomogeneity of the radiative flux perturbations produced by each geoengineering method.


Geoengineering by stratospheric SO2 injection: results from the Met Office HadGEM2 climate model and comparison with the Goddard Institute for Space Studies ModelE

Author(s): Jones A, Haywood J, Boucher O, Kravitz B, Robock A

Published: March, 2010

Publisher: Atmospheric Chemistry and Physics Discussions

DOI: 10.5194/acpd-10-7421-2010

Tags: Stratospheric Aerosols, Climate Modelling, Precipitation

URL: http://www.atmos-chem-phys-discuss.net/10/7421/2010/acpd-10-7421-2010.html

Abstract: We examine the response of the Met Office Hadley Centre's HadGEM2-AO climate model to simulated geoengineering by continuous injection of SO2 into the lower stratosphere, and compare the results with those from the Goddard Institute for Space Studies ModelE. The HadGEM2 simulations suggest that the SO2 injection rate considered here (5 Tg[SO2] yr−1) could defer the amount of global warming predicted under the Intergovernmental Panel on Climate Change's A1B scenario by approximately 30–35 years, although both models indicate rapid warming if geoengineering is not sustained. We find a broadly similar geographic distribution of the response to geoengineering in both models in terms of near-surface air temperature and mean June–August precipitation. The simulations also suggest that significant changes in regional climate would be experienced even if geoengineering was successful in maintaining global-mean temperature near current values.


Climate impacts of geoengineering marine stratocumulus clouds

Author(s): Jones A, Haywood J, Boucher O

Published: May, 2009

Publisher: Journal of Geophysical Research

DOI: 10.1029/2008JD011450

Tags: Environmental Side-Effects, Cloud Brightening, Climate Modelling, Precipitation, Cloud Physics

URL: http://www.agu.org/journals/ABS/2009/2008JD011450.shtml

Abstract: Theoretical potential geoengineering solutions to the global warming problem have recently been proposed. Here, we present an idealized study of the climate response to deliberately seeding large-scale stratocumulus cloud decks in the North Pacific, South Pacific, and South Atlantic, thereby inducing cooling via aerosol indirect effects. Atmosphere-only, atmosphere/mixed-layer ocean, and fully coupled atmosphere/ocean versions of the Met Office Hadley Centre model are used to investigate the radiative forcing, climate efficacy, and regional response of temperature, precipitation, and net primary productivity to such geoengineering. The radiative forcing simulations indicate that, for our parameterization of aerosol indirect effects, up to 35% of the radiative forcing due to current levels of greenhouse gases could be offset by stratocumulus modification. Equilibrium simulations with the atmosphere/mixed-layer ocean model, wherein each of the three stratocumulus sheets is modified in turn, reveal that the most efficient cooling per unit radiative forcing occurs when the South Pacific stratocumulus sheet is modified. Transient coupled model simulations suggest that geoengineering all three stratocumulus areas delays the simulated global warming by about 25 years. These simulations also indicate that, while some areas experience increases in precipitation and net primary productivity, sharp decreases are simulated in South America, with particularly detrimental impacts on the Amazon rain forest. These results show that, while some areas benefit from geoengineering, there are significant areas where the response could be very detrimental with implications for the practical applicability of such a scheme.


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