Oxford Martin School

On Wednesday 18 November Professor John Shepherd, Chair of the Royal Society's recent report on "Geoengineering the Climate" gave a lecture at the 21^st Century Ocean Institute. Professor Steve Rayner, Director of the Institute for Science, Innovation and Society (part of the 21^st Century School) was a member of the multidisciplinary group of 12 working experts who conducted the study for the Royal Society.

The report set out to provide "an independent scientific review of the range of methods proposed [for geoengineering the climate] with the aim of providing an objective view on whether geoengineering could, and should, play a role in addressing climate change, and under what conditions."

During his discussion of the report, Professor Shepherd divided potential geoengineering solutions into two broad categories:

• Solar Radiation Management (including mirrors in space, stratospheric aerosols, enhanced reflectivity of clouds and even painting all our roofs white)

• Carbon Dioxide Management (including ocean fertilisation, engineered carbon capture, enhanced weathering and the use of biochar)

The first category of approaches (SRM) would directly modify the radiation balance of the Earth, but without doing anything to reverse the original problem of high greenhouse gas emissions. It therefore creates a potentially serious new problem in which we would have to balance the effect of one major human intervention (emissions) with that of another (geoengineering). However, SRM techniques would be effective over a timescale of a few years and hence, could provide a useful solution in an emergency.

The second category (CDM) has the significant advantage of moving the environment back towards its natural state. This state of affairs is inherently less risky than the balancing act which would result form an SRM solution, as we already know what to expect if we return the environment to this state. It should also be noted that CDM approaches would address the problem of ocean acidification due to high CO2 levels, which SRM solutions could not tackle. However, all 'carbon dioxide management' approaches operate over a relatively long timescale and it would take many decades for them to reverse the damage already inflicted.

"Geoengineering the Climate" contains a more in depth review of each of these approaches, each of which is rated on effectiveness, timeliness, safety and affordability. (You can download a copy of the report here.)

The report concludes that all proposed geoengineering solutions run the risk of creating regional effects with regard to rainfall patterns, weather systems and ocean current. Professor Shepherd argued that a geoengineered solution to climate change could probably be achieved, but that this solution was far from ideal, due to the significant degree of uncertainty surrounding almost every aspect of the proposals. While geoengineering the climate is not an alternative to emissions reduction, he advised that more research be carried out, so that we could make appropriate and effective decisions in an emergency.

In the run up to December's climate change negotiations in Copenhagen, Professor Shepherd's message to the politicians was: try harder to reduce emissions, or else we may have to implement some of these methods. And we would much rather that we didn't have to.

A podcast of this event is available here and a video will be available shortly. We invite continued discussion of these issues below.