Dr Olivier Boucher, Head, Climate Chemistry and Ecosystems
Any scheme which aims to artificially and deliberately change the Earth's climate is called geoengineering. This includes everything from planting new forests to soak up greenhouse gases through to high-tech ideas, such as putting mirrors in space to reflect some of the Sun's rays.
Geoengineering has been put forward as a potential solution to climate change. It's thought some of the potential projects could help cool the planet, but this is very controversial. First of all, it's a developing area of science. As a result, there's a lot of uncertainty around how these projects might work and what their consequences may be. Some research suggests there could be major environmental consequences of tampering with our climate system.
Secondly, it is argued by some that we should be focused on the only sure way of tackling climate change, which is to cut greenhouse gas emissions. Looking at geoengineering may distract attention from that aim and create a false sense of security. However, because efforts to cut greenhouse gas emissions have so far been unsuccessful, geoengineering has become an increasingly important issue.
There are two types of geoengineering project:
Carbon dioxide removal (CDR) — removes carbon dioxide from the atmosphere and stores it, directly tackling the main cause of climate change. Examples of this include 'artificial trees' which chemically capture carbon from the atmosphere, or encouraging plankton growth in the oceans.
Solar radiation management (SRM) — changes the Earth's radiation balance, which means it can reduce (or increase) the amount of energy we get from the Sun. Examples of this are seeding clouds to make them brighter, or putting mirrors in space to reflect some solar rays away from Earth.
CDR should be safe, as it's just offsetting the extra greenhouse gases human activities are already putting in the atmosphere. It should also be effective, but only over longer timescales. The main problem is around their viability. Costs are likely to be high, and there may be other issues — planting forests means that land is not available for living space or growing crops.
On the other hand, research shows SRM could be effective in reducing temperatures and it should be relatively affordable. But there's a lot of uncertainty about how these techniques might impact the environment. For example, one Met Office study, Climate impacts of geoengineering marine stratocumulus clouds showed that seeding clouds off the coasts of southern Africa, South America and North America did slow down global warming by up to 25 years — but seeding one particular region also caused a knock-on effect which caused a 30% reduction in rainfall over the Amazon, posing a huge risk to this habitat. There could be other risks associated with other projects.
More research should allow us to get a better understanding of what the risks are and how we might be able to minimise them. Because this is such a complex area of climate science, however, it could be difficult to fully understand all the implications of a project — especially considering each project in each region will have its own impacts. Ultimately, it's unlikely that we can ever be sure we know all of the potential implications about any one project, so there's always going to be some degree of uncertainty. This means there's likely to be winners and losers from any SRM geoengineering scheme, and for the losers the consequences could be quite serious — such as possible drought or flooding. How countries would decide on how to compensate each other for these kind of issues could be an important political issue for the future.
Again, more research could reveal some techniques which are much less risky, but at the moment the choice appears quite straightforward. We can tackle climate change in a relatively safe way by reducing man-made greenhouse gas emissions, but if we fail to achieve the necessary cuts, geoengineering could be our only option. Most likely, that would have to be an SRM project and these come with very big scientific, political and financial issues attached. While intensive research into this area could change the situation in the future, currently the evidence suggests geoengineering should be regarded as a last resort in dealing with climate change.