Yet even as the 2C target has become a touchstone for the climate talks, scientific theory and real-world observations have begun to raise serious questions about whether the target is stringent enough.
For starters, the world has already warmed by almost one degree Celsius since the Industrial Revolution. That may sound modest, but as a global average, it is actually substantial. For any amount of global warming, the ocean, which covers 70 percent of the earth’s surface and absorbs considerable heat, will pull down the average. But the warming over land tends to be much greater, and the warming in some polar regions greater still.
The warming that has already occurred is causing enormous damage all over the planet, from
dying forests to
collapsing sea ice to
savage heat waves to
torrential rains. And scientists realize they may have underestimated the vulnerability of the ice sheets in Greenland and Antarctica.
Those ice sheets now appear to be in the early stages of breaking up. For instance, Greenland’s glaciers have lately been
spitting icebergs into the sea at an accelerated pace, and scientific papers published this year
warned that the melting in parts of Antarctica may already be unstoppable.
“The climate is now out of equilibrium with the ice sheets,” said
Andrea Dutton, a geochemist at the University of Florida who studies global sea levels. “They are going to melt.”
That could ultimately mean 30 feet, or even more, of sea level rise, though scientists have no clear idea of how fast that could happen.