Researchers asked leading experts on the Greenland and Antarctic ice sheets to provide their best updated estimates for the future of these frozen masses as temperatures spike. Aggregating these, the researchers concluded that the range of outcomes scientists now consider possible has shifted markedly toward more melting and, therefore, higher seas. For example, in a business-as-usual scenario, the median estimate from the United Nations’ last major climate report should have been more than doubled. In fact, the researchers found that it is unlikely, but plausible, that the oceans could rise a staggering 6½ feet by 2100 if emissions levels continue to be high. That would swamp roughly as much territory as is contained in all of Western Europe and make 187 million people homeless.
Since the United Nations’ last major climate assessment, the scientists watching the Earth’s major ice sheets have witnessed massive ice losses and tried to better model the way the sheets fracture, how liquid water interacts with the solid stuff, and the instability of ice cliffs. They have also done more to assess how these ice sheets behaved in previous warming epochs. They have not been able to provide more precise estimates for how bad things could get — they can still offer only a range of outcomes — except to say the outlook is worse than they thought previously. As with many effects of human-forced planetary warming, the precise nature of some consequences will be known only after they occur, when it is too late.
It is this sort of uncertainty that opponents of addressing global warming have played up to argue against action. Yet although it is possible to contemplate less-bad consequences at one unlikely end of the probability spectrum, it is also possible to foresee absolutely devastating results on the other end. And, as scientists have continued to refine their understanding of Earth systems, the distribution of the scenarios that seem probable has tended to move in the wrong direction.
President Trump and those in his administration ignore scientists’ increasingly dire warnings to the peril of their children, grandchildren and the rest of humanity.