Backup plan: The small print
Solar geo-engineering might enable us to stop global warming without cutting greenhouse gas emissions, but it could have side effects, such as reducing rainfall and altering climate patterns. It could also be expensive, and we’d need to maintain the geo-engineering project for decades or even centuries. Some people are concerned that focus on geo-engineering could divert resources from attempts to tackle climate change through mitigation and adaptation.
The effect of a reduction in sunlight on regional climates
Sunlight is more intense near the Equator than near the poles, so the Sun’s warming effect is most pronounced in tropical regions. In contrast, the heat-trapping potential of carbon dioxide (CO2) in the atmosphere is strongest near the poles. So while sunlight and CO2 both play a part in controlling the Earth’s temperature, their effects are concentrated in different regions of the globe. Scientists think it could be fairly straightforward – and certainly possible – to cancel out the global warming effect of extra CO2 by reducing sunlight. But cancelling out regional temperature changes is much more difficult and might not even be possible. So solar geo-engineering would probably alter local and regional climates.
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Solar geo-engineering could alter regional climate patterns
Image: NASA
The effect of a reduction in sunlight on rainfall
Global warming leads to other climate impacts, such as faster evaporation and changes in both the type and patterns of rainfall. These effects could be just as problematic as higher temperatures, potentially disrupting agriculture and water supplies. Would solar geo-engineering counteract these impacts? Rainfall is affected more by sunlight than by air temperature, so a reduction in sunlight is likely to change rainfall more than it will change temperature. Balancing out the increased temperatures resulting from higher carbon dioxide levels would require a larger reduction in sunlight than balancing out the effects of global warming on rainfall patterns. This means we’d have to decide which climate change impacts to counteract.
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Image: Steven Love / Fotolia
Solar geo-engineering and ocean acidification
When human activities emit carbon dioxide most of it accumulates in the atmosphere. But a large portion is also dissolved in the oceans, making the water more acidic. This is called ocean acidification and has already been observed around the world. Changes in ocean chemistry affect the creatures that live there. If we cool the planet by reducing sunlight but keep emitting carbon dioxide it will cause more and more acidification. Scientists think this could threaten many sea creatures, especially corals and some types of algae. Since these form the bottom of the marine food chain, acidification could threaten all the sea creatures that depend on them.
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Image: Quentin Houyoux / SXC
International decisions
A solar geo-engineering project would involve many choices that could impact on every country in the world: when to switch the system on, how much to sunlight block out, who should pay for it… Since the results would have profound implications for the whole word, all countries would probably want to have a say – and there could be many disagreements. Some countries might prefer warmer weather, only wanting to reduce sunlight a little. But countries facing more severe impacts from global warming might want a drastic reduction. Deciding on an approach that satisfies everyone could be a greater diplomatic challenge than figuring out how to reduce greenhouse gas emissions.
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Image: jan kranendonk / Shutterstock
The risks of breaking down or stopping early
Any solar geo-engineering project would need to be maintained for as long as carbon dioxide levels remain high – decades or even centuries. If we kept emitting carbon dioxide in the meantime, it would accumulate in the atmosphere. The resulting potential for warming would be counteracted by the reduction in sunlight. But if the geo-engineering system ever broke, or we decided to shut it down, scientists think global temperature would rise again – more rapidly than if we’d never implemented the geo-engineering project in the first place. Rapid changes are often more damaging. To avoid this risk, we’d have to be confident that we could maintain the geo-engineering system for as long as necessary.
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Image: cogal / NASA / iStockphoto
Prof John Shepherd
Professor John Shepherd chaired the Royal Society science policy study into geo-engineering which highlighted its potential benefits and drawbacks. ‘I would personally guess that there’s about a 50/50 chance that we shall actually need to use geo-engineering before the end of this century,’ says Professor Shepherd. ‘We’re failing to make enough progress in reducing emissions, and may achieve too little, too late. So we need to know whether any of these proposals may be a realistic option to help.’ With some people becoming enthusiastic about using geo-engineering, Professor Shepherd’s work helps separate science fact from science fiction, and improve our understanding of the possible role of geo-engineering.
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John Shepherd
