A key goal of international climate change policy, expressed in the UNFCCC, has been to "prevent dangerous anthropogenic interference with the climate system". For the past 20 years, that has been interpreted as limiting temperature increase to no more than 2°C beyond pre-industrial levels. All our modelling on emissions reduction has been focused around meeting this goal.
Yesterday, we found out that its not enough, with two papers reporting that the West Antarctic icesheet was already beyond the point of no return and would collapse:
A disaster may be unfolding—in slow motion. Earlier this week, two teams of scientists reported that the Thwaites Glacier, a keystone holding the massive West Antarctic Ice Sheet together, is starting to collapse. In the long run, they say, the entire ice sheet is doomed, which would release enough meltwater to raise sea levels by more than 3 meters.
One team combined data on the recent retreat of the 182,000-square-kilometer Thwaites Glacier with a model of the glacier’s dynamics to forecast its future. In a paper published online today in Science, they report that in as few as 2 centuries Thwaites Glacier’s outermost edge will recede past an underwater ridge now stalling its retreat. Their modeling suggests that the glacier will then cascade into rapid collapse. The second team, writing in Geophysical Research Letters (GRL), describes recent radar mapping of West Antarctica’s glaciers and confirms that the 600-meter-deep ridge is the final obstacle before the bedrock underlying the glacier dips into a deep basin.
Because inland basins connect Thwaites Glacier to other major glaciers in the region, both research teams say its collapse would flood West Antarctica with seawater, prompting a near-complete loss of ice in the area. “The next stable state for the West Antarctic Ice Sheet might be no ice sheet at all,” says the Science paper’s lead author, glaciologist Ian Joughin of the University of Washington (UW), Seattle.
What does 3 metres of sea-level rise mean? Hot Topic puts it succinctly: "we are going to have to say goodbye to the current coastline and everything built there". The timescale is long (though as we've found in the past, these things tend to speed up when we start looking at them closely), but in just a few human lifetimes, much of humanity is going to have to move.
And before anyone takes this as an excuse to simply give up trying to stop it, remember: this is one of the mild effects of human-induced climate change. Imagine what we'll get if we raise the temperature by the 3 or 4 degrees currently predicted for "business as usual"...