Climate model response from the Geoengineering Model Intercomparison Project (GeoMIP)

Solar geoengineering - deliberate reduction in the amount of solar radiation retained by the Earth - has been proposed as a means of counteracting some of the climatic effects of anthropogenic greenhouse gas emissions. We present results from Experiment G1 of the Geoengineering Model Intercomparison Project, in which 12 climate models have simulated the climate response to an abrupt quadrupling of CO<inf>2</inf> from preindustrial concentrations brought into radiative balance via a globally uniform reduction in insolation. Models show this reduction largely offsets global mean surface temperature increases due to quadrupled CO<inf>2</inf> concentrations and prevents 97% of the Arctic sea ice loss that would otherwise occur under high CO<inf>2</inf> levels but, compared to the preindustrial climate, leaves the tropics cooler (-0.3 K) and the poles warmer (+0.8 K). Annual mean precipitation minus evaporation anomalies for G1 are less than 0.2 mm day<sup>-1</sup> in magnitude over 92% of the globe, but some tropical regions receive less precipitation, in part due to increased moist static stability and suppression of convection. Global average net primary productivity increases by 120% in G1 over simulated preindustrial levels, primarily from CO<inf>2</inf> fertilization, but also in part due to reduced plant heat stress compared to a high CO<inf>2</inf> world with no geoengineering. All models show that uniform solar geoengineering in G1 cannot simultaneously return regional and global temperature and hydrologic cycle intensity to preindustrial levels. Key Points Temperature reduction from uniform geoengineering is not uniform Geoengineering cannot offset both temperature and hydrology changes NPP increases mostly due to CO2 fertilization ©2013. American Geophysical Union. All Rights Reserved.BK is
supported by the Fund for Innovative Climate and Energy Research.
Simulations performed by BK were supported by the NASA High-End
Computing (HEC) Program through the NASA Center for Climate
Simulation (NCCS) at Goddard Space Flight Center. The Pacific Northwest
National Laboratory is operated for the U.S. Department of Energy by
Battelle Memorial Institute under contract DE-AC05-76RL01830. AR is
supported by US National Science Foundation grant AGS-1157525. JMH
and AJ were supported by the joint DECC/Defra Met Office Hadley Centre
Climate Programme (GA01101). KA, DBK, JEK, UN, HS, and MS received
funding from the European Union’s Seventh Framework Programme (FP7/
2007–2013) under grant agreement 226567-IMPLICC. KA and JEK received
support from the Norwegian Research Council’s Programme for
Supercomputing (NOTUR) through a grant of computing time. Simulations
with the IPSL-CM5 model were supported through HPC resources of [CCT/
TGCC/CINES/IDRIS] under the allocation 2012-t2012012201 made by
GENCI (Grand Equipement National de Calcul Intensif). DJ and JCM thank
all members of the BNU-ESM model group, as well as the Center of
Information and Network Technology at Beijing Normal University for assistance
in publishing the GeoMIP data set. The National Center for Atmospheric
Research is funded by the National Science Foundation. SW was supported by
the Innovative Program of Climate Change Projection for the 21st century,
MEXT, Japan. Computer resources for PJR, BS, and JHY were provided by
the National Energy Research Scientific Computing Center, which is
supported by the Office of Science of the U.S. Department of Energy under
contract DE-AC02-05CH11231