One of the more innovative ideas for dealing with climate change is a sunshade - a giant screen in orbit which would disperse or block some of the sun's energy, reducing insolation and thereby lowering the Earth's temperature. However, there's a small snag: it wouldn't work. Or rather, it would not simply rewind the climate to a preindustrial state:
Dan Lunt of the University of Bristol, UK, and colleagues carried out the most detailed climate-modelling study to date on the impact of a sunshade. They simulated Earth's climate under three scenarios: pre-industrial times; a future climate with atmospheric carbon dioxide at an extreme level of four times pre-industrial values; and a sunshaded geo-engineered climate with the same high CO2 levels but solar radiation reduced by 4 per cent - similar to Cambrian times, 500 million years ago.This isn't just about the effectiveness of a sunshade, or its size and position. The key problem is that a higher carbon atmosphere leads to a different distribution of heat, and hence to a different climate. So if the aim is to prevent climate change and its resulting ecological effects (on, for example, food crops and endangered species), we need to actually reduce the amount of carbon we emit, and ideally start soaking it up.They found that Earth under a sunshade would not simply revert to its pre-industrial climate. Instead the tropics would be cooler than pre-industrial times by 1.5 °C, while high latitudes would be warmer by 1.5 °C, leading to less sea ice - bad news for animals that fish from the ice. Average precipitation would also drop by 5 per cent, according to the model.
