Slowing climate change by brightening clouds is harder than previously thought

Brightening clouds has been proposed as one way to artificially slow down climate change. In the method, sea water would be sprayed into the air above the oceans, and the resulting ice crystals would make the cloud reflect a greater part of solar radiation back into space. These kinds of clouds would appear whiter than before in satellite pictures.

In climate model studies conducted so far it has been assumed that the salt particles would spread evenly over an area of up to thousands of square kilometres, and that their numbers would not be significantly reduced by collisions of the particles with each other. In a study that has now been published, it was observed that collisions near the source of the spraying typically reduce the total number of the particles by more than 50 percent. When this was considered in the climate model, the cooling effect from cloud brightening was reduced by half. "The outcome indicates that slowing climate change by brightening clouds is more challenging than previously estimated", says Antti-Ilari Partanen, a researcher at the Finnish Meteorological Institute.

The study was conducted in cooperation with Dalhousie University (Canada), the University of Leeds (Great Britain) and Colorado State University (USA). It was partly financed by the COOL project of the Academy of Finland, which is part of the Academy's climate research programme.

Further information:

Researcher Antti-Ilari Partanen, tel. +358 50 448 3226, antti-ilari.partanen@fmi.fi

Reference:G. S. Stuart, R. G. Stevens, A.-I. Partanen, A. K. L. Jenkins, H. Korhonen, P. M. Forster, D. V. Spracklen, and J. R. Pierce (2013), Reduced efficacy of marine cloud brightening geoengineering due to in-plume aerosol coagulation: parameterization and global implications, Atmos. Chem. Phys., 13, 10385-10396.

http://www.atmos-chem-phys.net/13/10385/2013/acp-13-10385-2013.html