Geoengineering no quick fix for sea-level rise
24 August 2010, by Tamera Jones
Sea levels are still likely to rise by at least 30cm by the end of 2100, compared with 2000 levels, unless we use the most extreme geoengineering solutions to ease climate change while also cutting CO2 emissions, say researchers.
Computer artwork of a large mirror (circular) in Earth orbit. The mirror is designed to shield the Earth (lower right) from the Sun (behind mirror), in an attempt to control changes in the climate of the Earth.
This is because the huge volume of the oceans means they take a long time to react fully to atmospheric temperatures - usually about a century.
'Geoengineering could be a simple solution for global temperatures, but not for sea-level rise,' explains Dr Svetlana Jevrejeva from the National Oceanography Centre, one of the co-authors of the report. 'Even with extreme scenarios, we'd only see a small slowing of sea levels.'
Jevrejeva and colleagues from China, Finland and Denmark wanted to see how five geoengineering solutions will affect sea levels. Geoengineering falls into two main types: limiting the effect of the sun's rays, or changing the carbon cycle in some way. The former doesn't change atmospheric CO2 levels in any way, whereas the latter does.
The team used a well-established model to look at the effect of firing a large amount of sulphur dioxide into the atmosphere, putting mirrors in space, planting huge numbers of trees, biochar (turning plants into a type of charcoal in soil where they boost crop productivity) and switching to bioenergy. They investigated how these methods would affect climate change under different CO2 emissions scenarios.
They found that using bioenergy for power while capturing the emitted CO2 and storing it deep underground is likely to be the least risky and the most publicly acceptable solution to tackle climate change. This would also lead to fewer fossil fuels being burnt for energy. But this solution wouldn't be as effective as using aerosols or giant mirrors in space at slowing sea level rise.
'Even with extreme [geoengineering] scenarios, we'd only see a small slowing of sea levels.'
Dr Svetlana Jevrejeva from the National Oceanography Centre
Firing as much sulphur dioxide into the atmosphere as the eruption of Mount Pinatubo did, every 18 months, could slow sea level rise by 40 to 80 years, they discovered. But the effects of pumping so much sulphur dioxide into the sky are unknown.
'We don't know how aerosols will affect ecosystems and the climate,' says Jevrejeva. 'But they're likely to disrupt rainfall patterns and stratospheric ozone.'
Erecting mirrors in space to reflect the sun's rays, on the other hand, is a nice, clean idea and could limit sea level rise, but it would be prohibitively expensive. This isn't only because of the costs of getting the mirrors into space, but also because of the maintenance required to keep them going.
'Another problem with mirrors in space is that these kinds of geoengineering solutions do nothing to address CO2 levels in the atmosphere. If the mirrors broke down, temperatures would still rise and we'd be back to where we started,' says Jevrejeva.
Jevrejeva and her colleagues conclude that the most effective strategy to reduce the rate of sea-level rise would be to use two different approaches, such as using bioenergy as a source of fuel and capturing CO2 for long-term storage.
But if we don't use any geoengineering solutions at all, we'd see sea levels rise by 0.6 to 1.1m, says Jevrejeva.
'The most important message from this is that we still have to address the underlying problem: atmospheric CO2 levels,' she adds.
Sea-level rise could be the most damaging result of rising temperatures, with around 150 million people living within one metre of high tide across the world.
The results are published in Proceedings of the National Academy of Sciences.
J. C. Moore, S. Jevrejeva, A. Grinsted, Efficacy of geoengineering to limit 21st century sea-level rise, Proceedings of the National Academy of Sciences, published online before print August 23, 2010, doi: 10.1073/pnas.1008153107
Keywords:
Atmosphere,
Environmental change,
Oceans,
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