Ecosystem risks from global average temperature increase (IPCC AR4, 2007)

Greenhouse gas concentrations have risen to unprecendented levels (IPCC AR4, 2007)

Minimum arctic sea-ice volume is falling precipitously. Some scientists believe summer sea ice may disappear in the arctic by 2015 (PIOMAS, 2011)

Feedbacks between climate change, desertification, and biodiversity loss (Millenium Ecosystem Assessment, 2005)

Reducing emissions of greenhouse gases is the safest way to counter climate change. While reducing emissions of greenhouse gases is necessary – indeed essential – it may not be sufficient to maintain a stable climate and healthy oceans.

We do not know for certain what level of greenhouse gases in the atmosphere is compatible with a stable climate and healthy oceans, but many scientists believe that stabilising at 450 parts per million volume of carbon dioxide (eqv) would give us a 50:50 probability of limiting increases in global mean temperature below 2 degrees Celcius, the threshold for ‘dangerous’ climate change.

So, there are two uncertainties:

• The level at which we will manage to stabilise greenhouse gases. This is a function of political will and technical ability.
• The responsiveness of the climate system to increased greenhouse gas levels. We may be lucky and have a small climate response to a large change in greenhouse gases. Or we may be unlucky and have a large climate response to a small change in greenhouse gases. No-one knows for sure.

If humans continue on the current emissions path and are unlucky and the climate response is large, amplified by feedbacks, or the ability of human and natural systems to adapt is insufficient the consequences could be dire for people and the planet.  It is possible that by deploying geoengineering we may be able to forestall these consequences and to protect critically vulnerable natural ecosystems such as the arctic, or coral reefs from damage that otherwise could no longer be avoided.

Given the uncertainties and stakes involved, it is important that we conduct research to determine if any of the proposed geoengineering techniques could be employed without creating countervailing side-effects. It is far from certain that any of them could be, so it would be extremely unwise to rely on geoengineering as a ‘silver bullet’ for climate change.