What is Geoengineering?

This week I was at the Royal Society meeting on Geoengineering. One of the speakers, Nicholas Pidgeon, talked about research on normal people’s attitudes towards geoengineering. What I thought was interesting was that what he found was that most people don’t know anything about geoengineering. People frequently confused it with geothermal heating. My unrepresentative sample of my friends (who I’ve surely bored on this subject before now?) showed that geoengineering was thought to be something to do with geology, probably an engineering/geology mix. Well, you can’t fault the logic can you?

So I think it’s worth addressing this misconception about geoengineering.

Geoengineering is the “large-scale engineering of our environment in order to combat or counteract the effects of [human made] changes in atmospheric chemistry” (Lenton, 2009). Nothing to do with rocks. Note, this is not mad scientists trying to control the climate for fun. Geoengineering is involved with trying to prevent the worst effects of the climate change problem we’ve created. All geoeningeering is still purely hypothetical. It’s not going to replace the need for reducing emissions, or transferring to a low carbon economy. It is also worth noting that there are two essential types of geoengineering: either schemes remove CO2 from the atmosphere, or they increase the earth’s albedo (to reflect more heat away). The concerns, possible side effects and costs associated with each are very different.

Geoengineering schemes which reduce atmospheric CO2 (also known as Carbon Capture and Storage, or CCS) have essentially the same effect as conventional mitigation (reducing carbon emissions). Removal of CO2 could occur in three areas: terrestrial, oceanic or atmospheric. Land based schemes, such as large scale afforestation (Nilsson, 1995) increase vegetation uptake of CO2 and carbon storage. However, paradoxically, afforestation may have a neutral or even positive net radiative forcing as forests have lower albedo than grass land (Betts, 2000a). Ocean schemes, such as iron fertilisation of the southern ocean (Martin, 1994), sequester carbon into the deep ocean, but are fraught with controversies (Chisholm, 2001). Atmospheric removal of CO2 is via chemical ‘scrubbing’ from the atmosphere where the resultant carbonate is put into long term storage (Zeman, 2007), but the technology is still developing for this, and the cost is likely to be high.

Increasing the earth’s albedo (sometimes known as Solar Radiation Management, or SRM) is generally more controversial than CCS. SRM can be achieved by: increasing reflection in the atmosphere; increasing albedo above the Earth in space; or by increasing ground albedo (Lenton, 2009). The atmosphere or above atmosphere schemes are the most controversial. Above the atmosphere, reflection of heat could be achieved with mirrors in space as a ‘sunshade’ (Lunt, 2008). Within the atmosphere, an increase in aerosols (very small particles, not the stuff in deodorant bottles) which reflect light could have a similar effect (Rasch, 2008). Naturally, there are concerns about the feasibility, desirability, cost and side effects of such schemes.

For surface albedo changes the effects are more localised and less permanent than space based SRM schemes. Various methods of increasing surface albedo have been proposed, including increasing the albedo of urban areas (Akbari, 2009); grass land (Hamwey, 2007); or cropland (Ridgwell, 2009). The cooling potential of ground albedo changes is substantially less than those above the ground, because of the surface area available. However, the risk is also considerably less too.

Geoengineering is not something that would (I hope) be undertaken lightly. But in the face of serious climate change and total inertia on carbon emissions, it is something that could be part (note: part – not all) of the solution.