Shading Earth鈥檚 surface from sunlight could postpone or even avoid the collapse of the West Antarctic ice sheet 鈥� but only if we start soon and only in conjunction with substantial emissions cuts, according to two computer modelling studies by independent teams.
鈥淭here鈥檚 a time window that we can do this, and if we dither, there鈥檚 just no point in doing it,鈥� says at the University of Lapland in Finland, who led one of the teams. 鈥淎nd that time window I think is a hell of a lot closer to 25 years than it is to 100 years.鈥�
鈥淭he study we did says 2030 at the latest,鈥� says at the Alfred Wegener Institute in Bremerhaven, Germany.
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However, neither Moore nor Sutter is suggesting we rush ahead with geoengineering, not least because there are still far too many unknowns. Neither do they think there is any chance of achieving the necessary political consensus.
鈥淭o be handled well, you would have to coordinate efforts among nations which are not known for coordinating things well,鈥� says Sutter. 鈥淎nd if you stop geoengineering for a year or two, you would have a termination shock,鈥� he adds, meaning the climate would suddenly get much hotter.
The West Antarctic ice sheet is known to be vulnerable to collapse because it rests on the seabed rather than land above sea level, meaning it can be melted from below by relatively warm water. What鈥檚 more, this seabed becomes deeper further back, meaning once the ice sheet begins to retreat, an ever-larger area of ice will be exposed to the warm water and the melting will accelerate.
Previous studies suggest we are rapidly approaching the tipping point beyond which the collapse of the West Antarctic ice sheet becomes inevitable, which will add more than 3 metres to the already-rising global sea level.
鈥淲e鈥檙e in this terrible situation where we鈥檙e walking along this cliff edge,鈥� says Moore. 鈥淎nd we know that we are very, very close to it.鈥�
To find out if we can avoid this collapse, Moore, Sutter and their colleagues used computer models to explore the effects of using aeroplanes to spread sulphate aerosols that would reflect sunlight back into space.
Sutter鈥檚 team fed the output from a global climate model run until 2300 into a model of the Antarctic ice sheet. The researchers found that avoiding ice sheet collapse required either drastic emissions cuts or geoengineering to begin almost immediately.
鈥淏ut it鈥檚 way too early to make conclusive statements,鈥� says Sutter. Different climate models will produce somewhat different results, he says.
Moore鈥檚 team didn鈥檛 use an ice sheet model, but did use six different global climate models, run until 2100. The researchers found that adding sulphate to the atmosphere speeds up the winds that circle the pole, keeping warming waters away from the edge of the ice sheet.
Sutter and Moore presented their findings at a meeting of the European Geosciences Union in Vienna, Austria, on 18 April.
鈥淚 think we鈥檙e pretty much in agreement, it鈥檚 just that [Sutter is] using different models,鈥� says Moore. 鈥淲e absolutely do agree that the earlier you do something, the better the chance of it actually working.鈥�
One reason why climate models differ in their projections is because there are so few actual observations from the area around West Antarctica. 鈥淲e have one or two unmanned submarines when we need a hundred,鈥� says Moore. 鈥淭his is super high-priority stuff.鈥�
What is also clear is that once we pass this tipping point, there is no going back. The only way to make the ice sheet regrow would be to cool the planet down to the temperature it was during the last ice age, says Sutter. 鈥淣o one wants that.鈥�
But with the world currently failing to cut emissions, the chance of avoiding the collapse of the ice sheet appears low, he says. How bad the outcome will be depends in part on how fast it happens, which is another big uncertainty.
鈥淚f it takes centuries, then maybe there鈥檙e ways to adapt,鈥� says Sutter. 鈥淣ot for low-lying island states, but for other coastlines.鈥�
Moore says it isn鈥檛 the job of scientists to decide whether to resort to geoengineering. But a lot more research on the West Antarctic ice sheet and the effects of geoengineering is urgently needed to provide the data needed for leaders to make an informed judgement, he says.
