Tackling sea level rises though geoengineering won't work, and would impose enormous risks on future generations, according to an international research team.
Sea levels will likely be at least 30 centimetres higher by 2100 than at the start of the century, even if all but the most aggressive geoengineering schemes are carried out and greenhouse gas emissions are tightly controlled.
"Rising sea levels caused by global warming are likely to affect around 150 million people living in low-lying coastal areas, including some of the world’s largest cities," says Dr Svetlana Jevrejeva of the UK's National Oceanography Centre.
Jevrejeva and her colleagues modelled sea levels over the 21st century under various geoengineering schemes and carbon dioxide emission scenarios.
"We used 300 years of tide gauge measurements to reconstruct how sea level responded historically to changes in the amount of heat reaching the Earth from the sun, the cooling effects of volcanic eruptions, and past human activities," said Jevrejeva. "We then used this information to simulate sea level under geoengineering schemes over the next 100 years."
They found that sea-level variations caused by events such as severe volcanic eruptions were generally much smaller than those caused by man-made carbon dioxide emissions, even under the more effective geoengineering schemes.
Injecting sulfur dioxide particles into the upper atmosphere would reduce temperature and delay sea-level rise by 40 to 80 years, and could keep sea levels close to those of 1990.
However, they say, this would be costly and also risky, as the effects on ecosystems and the climate system are poorly understood.“We simply do not know how the Earth system would deal with such large-scale geoengineering action,” said Jevrejeva.
Large mirrors orbiting the Earth could deflect more of the sun’s energy back out to space, reducing temperatures and helping control sea level. But the logistics and engineering challenges of such a scheme are enormous, says the team.
The most effective measure, the team found, is bioenergy with carbon storage (BECS). Biofuel crops could be grown on a large-scale, and carbon dioxide released during their combustion or fermentation could be captured, and the carbon stored as biochar in the soil or in geological storage sites.
"Substituting geoengineering for greenhouse emission control would be to burden future generations with enormous risk," said Jevrejeva.