Geoengineering techniques for countering climate change have been receiving much press recently as a `Plan B' if a global deal to tackle climate change is not agreed at the COP15 negotiations in Copenhagen this December. However, the field is controversial as the methods may have unforeseen consequences, potentially making temperatures rise in some regions or reducing rainfall, and many aspects remain under-researched.

This focus issue of Environmental Research Letters is a collection of research articles, invited by David Keith, University of Calgary, and Ken Caldeira, Carnegie Institution, that present and evaluate different methods for engineering the Earth's climate. Not only do the letters in this issue highlight various methods of climate engineering but they also detail the arguments for and against climate engineering as a concept.

Further reading
Focus on Geoengineering at http://environmentalresearchweb.org/cws/subject/tag=geoengineering
IOP Conference Series: Earth and Environmental Science is an open-access proceedings service available at www.iop.org/EJ/journal/ees

Focus on Climate Engineering: Intentional Intervention in the Climate System Contents

Modification of cirrus clouds to reduce global warming
David L Mitchell and William Finnegan

Climate engineering and the risk of rapid climate change
Andrew Ross and H Damon Matthews

Researching geoengineering: should not or could not?
Martin Bunzl

Of mongooses and mitigation: ecological analogues to geoengineering
H Damon Matthews and Sarah E Turner

Toward ethical norms and institutions for climate engineering research
David R Morrow, Robert E Kopp and Michael Oppenheimer

On the possible use of geoengineering to moderate specific climate change impacts
Michael C MacCracken

The impact of geoengineering aerosols on stratospheric temperature and ozone
P Heckendorn, D Weisenstein, S Fueglistaler, B P Luo, E Rozanov, M Schraner, L W Thomason and T Peter

The fate of the Greenland Ice Sheet in a geoengineered, high CO₂ world
Peter J Irvine, Daniel J Lunt, Emma J Stone and Andy Ridgwell

Assessing the benefits of crop albedo bio-geoengineering
Joy S Singarayer, Andy Ridgwell and Peter Irvine

Can we control El Niño?
Douglas G MacMynowski

Geoengineering by cloud seeding: influence on sea ice and climate system
Philip J Rasch, John Latham and Chih-Chieh (Jack) Chen

This focus issue is not yet complete, there are still letters at press and in review.