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摘要

We all know the arguments. Greenhouse-gas levels are rising. The planet is warming up. The climate is changing, with strange patterns of extreme weather, melting ice and engulfing deserts. According to some, we may be approaching - or even past - a tipping point where effects feed off each other and climate change accelerates. What should we do about this? For years now, the answer has been clear: reduce greenhouse-gas emissions. Increasingly drastic targets have been set by many governments for cutting the CO_2 emitted from power stations and transport by increasing efficiency and reducing consumption. However, CO_2 levels continue to rise. The heat is onrnand what was once seen as crackpot fringe science, strictly for pulp fiction, has now started to seem more plausible: geoengineering.rnIt is a term that has many meanings, but, for the purposes of combating climate change, it is the use of technology to cool down the planet. There are two main methods of doing this. One is reversing the greenhouse effect by pulling CO_2 out of the atmosphere and locking it away in a planetary version of a carbon capture and storage (CCS) scheme. That may sound ambitious, but it is nothing compared to the other option: create a giant sunshade to prevent some of the sun's rays from hitting the atmosphere in the first place.