Climatic side effects of geoengineering solutions

Computational Earth system models are used for simulations of the climatic impact of solar radiation management. Robust features can be detected by applying different models. Several state-of-the-art Earth system models simulate the impact of climate engineering. This GeoMIP experiment G1 mimics mirrors in space and reduces the incoming solar radiation at the surface. The radiative forcing from an instantaneous quadrupling of the CO2 concentration (4xCO2), 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 control state, the preindustrial climate. While the global mean surface air temperature in G1 remains almost unchanged compared to the control simulation, regionally the temperature is decreased in the tropics and rises in polar regions. Therefore, the equator to pole 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. These robust results of the model ensemble show that an engineered climate would not be the same as natural conditions, mainly because of the reduced solar radiation at surface. (See Schmidt et al (2012); Kravitz et al (2013))

Niemeier et al (2013) compare the impact of different geoenineering techniques, among them the injection of sulfur into the stratosphere, mirrors in space, and marine cloud brightening  through artificial emissions of sea salt. This study focuses on the question to what extent climate impacts of these three methods would be different. While global mean temperature increases slightly due to the inertia of the climate system and evolves very similar with time, responses of global mean precipitation differ considerably among the methods. The hydrological sensitivity is decrease d by SRM, most prominently for sea salt emissions, followed by the injection of sulfate into the stratosphere. A summary of the article was published as an EOS spotlight: Comparing climate impact of different geoengineering methods.

Jones et al (2013) shows the consequences of a sudden termination of geoengineering. The temperature increases in all models imediately after termination and reaches 60 to 100 % of the temperature in a non-geoengineered simulation within five years. Tilmes et al (2013) show changes in the monsoon as a consequence of SRM, Xia et al (2014) applies a Decision Support System for Agrotechnology Transfer (DSSAT) crop model to learn more about the impact on the growth rate of rice and corn in China.


General implications

Geoengineering suggestions have been criticized heavily, in particular as they try to cure the symptoms of global climate change and not its causes. Allan Robock (2008) listed reasons pro and con:

  • In the case of engineering radiation it might be possible to limit global temperature increase, but acidification of oceans as a consequence of increasing CO2 levels would not be stopped.
  • Another problem is the long lifetime of atmospheric CO2 that would make it necessary to sustain geoengineering for periods of hundreds to thousands of years if no other technical way to remove CO2 from the atmosphere were to be found.
  • Political and psychological concern exists that considering geoengineering might distract or prevent people from studying and investing in options to reduce the emission of GHGs.
  • International law regulations will be necessary.
  • One of the first questions to be raised: Who's hand on the thermostate?


Jones, A., J. M. Haywood, K. Alterskjær, O. Boucher, J. N. S. Cole, C. L. Curry, P. J. Irvine, D. Ji, B. Kravitz, J. E. Kristjánsson, J. C. Moore, U. Niemeier, A. Robock, H. Schmidt, B. Singh, S. Tilmes, S. Watanabe, and J.-H. Yoon, The impact of abrupt suspension of solar radiation management (termination effect) in experiment G2 of the Geoengineering Model Intercomparison Project (GeoMIP), Journal of Geophysical Research, submitted.

Kravitz et al.: Climate model response from the Geoengineering Model Intercomparison Project (GeoMIP), JGR, DOI: 10.1002/jgrd50646, 2013

Niemeier, U., H. Schmidt, K. Alterskjær, and J. E. Kristjánsson, Solar irradiance reduction via climate engineering--climatic impact of different techniques, Journal of Geophysical Research, submitted.

Schmidt, H. et al.: Solar irradiance reduction to counteract radiative forcing from a quadrupling of CO2: climate responses simulated by four earth system models, Earth Syst. Dynam., 3, 63-78, doi:10.5194/esd-3-63-2012, 2012.

Robock, Alan, 2008:  20 reasons why geoengineering may be a bad idea.  Bull. Atomic Scientists, 64, No. 2, 14-18, 59, doi:10.2968/064002006

Royal Society: Geoengineering the climate: science, governance and uncertainty