Living with climate change: What's the worst that can happen?
来源：未知 作者：綦毋浯埝 时间：2019-04-04 11:17:01
Jim Yungel/NASA By Fred Pearce and Alice Klein IN ANTARCTICA, the giant Thwaites glacier is in fast retreat. Ditto the Jakobshavn and Zachariae Isstrom glaciers in Greenland. Climate researchers worry they may have passed their tipping points, beyond which change feeds on itself and cannot be stopped. If the three glaciers melted fully, they alone would commit the world to more than 2 metres of sea level rise. The Intergovernmental Panel on Climate Change has warned that rapid warming could take key Earth systems beyond their tipping points, part of the worst-case scenario of climate change. Tim Lenton of Exeter University, UK, says a threshold was passed in 2007 when the summer melt of Arctic sea ice accelerated. The fear is that, with less ice cover, the ocean will absorb more heat and prevent winter refreeze, locking the system into perpetual decline. This is not the only system at risk. Historically, as temperatures have gone up, changing amounts of sea ice at the poles have caused ocean circulation to flip. A new flip could lose us the Gulf Stream and collapse the Asian and West African monsoons, affecting the livelihoods of billions. So far, annual changes in sea ice have not disturbed overall global ocean circulation. But the Atlantic leg has already weakened markedly,