Do we need geoengineering?

Mike Childs

21 June 2011

Do we need to use geo-engineering to cool the planet? This is the question an expert working group of the Intergovernmental Panel on Climate Change (IPCC) is discussing as it meets in Peru this week .

 Firstly it is important to recognise that we may be already committed to global temperature increases of around 1.5 degrees above preindustrial level. A review of climate science published by the Committee on Climate Change last December showed that the impacts from a 2 degree temperature increase - the level politicians believe is a 'safe' limit - were greater than previously thought.  In fact, a 1.5 degree temperature target - or less - is a much more appropriate target if we want to avoid dangerous climate change; i.e. crossing tipping points such as the melting of the Greenland ice sheet or release of vast quantities of methane from Siberian permafrost.

So if we are already committed to a 1.5 degree rise - and if to avoid dangerous climate change we need to keep temperature increases to 1.5 degrees or less - then surely the answer is yes, we do need geo-engineering? Not exactly.

Scientists don't yet know with very high certainty that we are committed to 1.5 degrees. It all depends on how sensitive the climate is to greenhouse gases and we aren't totally sure about that. If we are lucky the planet may be less sensitive and we may only be committed to, say, a 1.2 degrees increase. If this were the case then a herculean effort on cutting emissions might just enable us to avoid 1.5 degrees without geo-engineering.  However, as our report Reckless Gamblers showed, the scale of emissions cuts required is probably technically and politically impossible. So whilst theoretically, if we are lucky, we could possibly stop dangerous climate change without geo-engineering, in practice - we can't.

But to say yes to geo-engineering is to say yes to technologies that range from the mad, bad and dangerous to technologies that may bring benefits beyond climate change (for example to wildlife). It is clearer to talk about solar radiation management (SRM) technologies that reflect the Sun's energy back into space and Negative Emissions technologies (NETs) which take carbon pollution out of the atmosphere.

Most SRM technologies fit into the mad, bad and dangerous category. For example firing aerosols into the stratosphere may well reflect some of the Sun's energy but it could also severely disrupt the monsoons on which hundreds of millions of people depend on for their livelihoods. As a rule of thumb SRM technologies should not be deployed.

NETs are different. Some bring big potential risks. For example converting vast areas of land to produce biomass for burning with carbon capture and storage will take carbon out of the atmosphere but may also lead to major losses in biodiversity and rapidly escalating food prices. Other techniques, such as using chemicals in 'artificial trees' to capture carbon from the atmosphere should be deployed once developed. Better soil management and restoring peat bogs are no brainers.

So the IPPC experts shouldn't conclude we need geo-engineering. They should conclude that some NETs need support and development. But before these are deployed on a large-scale it is important that international governance issues are resolved and risks well understood, as agreed by the Convention on Biological Diversity last year.

FOOTNOTE ON SUNSPOTS - reports this week suggested that the planet may be cooled over coming decades as a result of fewer sunspots. Scientists' understanding of this is limited to say the least. If there is some cooling it is thought to be in the order of 0.5 degrees. This won't be much of a respite if projections of a 4 degree rise or more are correct.