Human interventions to alter the climate in an attempt to reduce sea-level rises will fail, researchers have predicted.
As climate change negotiations continue to prove slow and unambitious, large-scale geoengineering plans to alter the world's climate have started to gain support.
The two main options involve limiting incoming solar radiation, through the use of mirrors or by increasing cloud cloud cover, and modifying carbon levels though afforestation or growing plants and then capturing and storing carbon dioxide released during burning or fermentation.
Now a new analysis by researchers from China, Denmark and the UK looked at historical measurements over the past 300 years to see how sea levels responded to climatic changes. The scientists then used this information to predict the likely effect of the various man-made proposals to change the climate over the next 100 years.
They found that even if all but the most aggressive geoengineering schemes were undertaken to mitigate the effects of global warming, sea levels would still be 30-70 cm higher by 2100 than they were at the start of the century.
It would take an injection of sulphur dioxode particles equivalent to a major volcanic eruption, such as that of Mt Pinatubo, every 18 months to reduce temperatures and delay ice-cap melt and sea-level rises.
But study co-author Dr Svetlana Jevrejeva, of the National Oceanography Centre (NOC), said even then many of the proposals, such as injecting sulphur dioxide particles into the atmosphere to reduce global warming, were 'risky' because of their unknown effect on ecosystems.
'There are serious unknowns. We simply do not know how the Earth system would deal with such large-scale geo-engineering action. Substituting geo-engineering for greenhouse emission control would be to burden future generations with enormous risk,' she said.
Jevrejeva said the least risky option of limiting sea-level rises was by growing plants and then capturing and storing their carbon.
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