The hydrological impact of geoengineering in the Geoengineering Model Intercomparison Project (GeoMIP)

The hydrological impact of enhancing Earth's albedo by solar radiation management is investigated using simulations from 12 Earth System models contributing to the Geoengineering Model Intercomparison Project (GeoMIP). We contrast an idealized experiment, G1, where the global mean radiative forcing is kept at preindustrial conditions by reducing insolation while the CO <inf>2</inf> concentration is quadrupled to a 4×CO<inf>2</inf> experiment. The reduction of evapotranspiration over land with instantaneously increasing CO<inf>2</inf> concentrations in both experiments largely contributes to an initial reduction in evaporation. A warming surface associated with the transient adjustment in 4×CO<inf>2</inf> generates an increase of global precipitation by around 6.9% with large zonal and regional changes in both directions, including a precipitation increase of 10% over Asia and a reduction of 7% for the North American summer monsoon. Reduced global evaporation persists in G1 with temperatures close to preindustrial conditions. Global precipitation is reduced by around 4.5%, and significant reductions occur over monsoonal land regions: East Asia (6%), South Africa (5%), North America (7%), and South America (6%). The general precipitation performance in models is discussed in comparison to observations. In contrast to the 4×CO<inf>2</inf> experiment, where the frequency of months with heavy precipitation intensity is increased by over 50% in comparison to the control, a reduction of up to 20% is simulated in G1. These changes in precipitation in both total amount and frequency of extremes point to a considerable weakening of the hydrological cycle in a geoengineered world. Key Points Geoengineering leads to a weakening of the hydrologic cycle Evapotranspiration changes important for initial reduction of precipitation Considerable reduction of monsoonal precipitation over land with SRM ©2013. American Geophysical Union. All Rights Reserved.We thank all participants of the Geoengineering
Model Intercomparison Project and their model development
teams, the CLIVAR/WCRP Working Group on Coupled Modeling for
endorsing GeoMIP, and the scientists managing the Earth System Grid
data nodes who have assisted with making GeoMIP output available. We
further acknowledge the World Climate Research Programme’s Working
Group on Coupled Modelling, which is responsible for CMIP, and we
thank the climate modeling groups for producing and making available
their model output. For CMIP, the U.S. Department of Energy’s Program
for Climate Model Diagnosis and Intercomparison provides coordinating
support and led development of software infrastructure in partnership
with the Global Organization for Earth System Science Portals. We thank
the TRMM Online Visualization and Analysis System (TOVAS) and the
GPCC Global Precipitation Climatology Centre for providing the rainfall
data set. The participation of J. Fasullo is supported by NASA Award
NNG06GB91G. J. Haywood and A. Jones were supported by the joint
DECC/Defra Met Office Hadley Centre Climate Programme (GA01101). K.
Alterskjær, D. B. Karam, J. E. Kristjánsson, U. Niemeier, H. Schmidt, and
M. Schulz received funding from the European Unions Seventh Framework
Programme (FP7/2007-2013) under grant agreement 226567-IMPLICC.
K. Alterskjær and J.E. Kristjánsson received support from the Norwegian
Research Council’s Programme for Supercomputing (NOTUR) through a
grant of computing time. B. Kravitz is supported by the Fund for Innovative
Climate and Energy Research. Simulations performed by B. Kravitz were
supported by the NASA High-End Computing (HEC) Program through the
NASA Center for Climate Simulation (NCCS) at Goddard Space Flight
Center. Computer resources for P.J. Rasch, B. Singh, and J.-H. Yoon 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. J.-H. Yoon was further supported
by the NERSC. D. Ji and J. Moore 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. H. Muri was supported by the EU 7th Framework Programme
grant agreement 306395, EuTRACE. A. Robock is supported by
the U.S. National Science Foundation grant AGS-1157525. S. Watanabe
was supported by SOUSEI Program, MEXT, Japan, and the Earth Simulator
was used for the simulations of MIROC-ESM. Finally, we thank
Gary Strand for CCSM4 output formatting and James Hurrell for supporting
this study. The National Center for Atmospheric Research is funded by
the National Science Foundation. We thank all reviewers and Govindasamy
Bala for useful suggestions to the paper