NYReview of Books, by Bill McKibben:
Though it was published at the beginning of October, Global Warming of 1.5°C, a report by the Intergovernmental Panel on Climate Change (IPCC), is a document with its origins in another era, one not so distant from ours but politically an age apart. To read it makes you weep not just for our future but for our present.
The report was prepared at the request of the United Nations Framework Convention on Climate Change at the end of the Paris climate talks in December 2015. The agreement reached in Paris pledged the signatories to
holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change.
The mention of 1.5 degrees Celsius was unexpected; that number had first surfaced six years earlier at the unsuccessful Copenhagen climate talks, when representatives of low-lying island and coastal nations began using the slogan “1.5 to Stay Alive,” arguing that the long-standing red line of a two-degree increase in temperature likely doomed them to disappear under rising seas. Other highly vulnerable nations made the same case about droughts and floods and storms, because it was becoming clear that scientists had been underestimating how broad and deadly the effects of climate change would be. (So far we’ve raised the global average temperature just one degree, which has already brought about changes now readily observable.) …
The takeaway messages are simple enough: to keep warming under 1.5 degrees, global carbon dioxide emissions will have to fall by 45 percent by 2030, and reach net zero by 2050. We should do our best to meet this challenge, the report warns, because allowing the temperature to rise two degrees (much less than the 3.5 we’re currently on pace for) would cause far more damage than 1.5. At the lower number, for instance, we’d lose 70 to 90 percent of coral reefs. Half a degree higher and that loss rises to 99 percent. The burden of climate change falls first and heaviest on the poorest nations, who of course have done the least to cause the crisis. At two degrees, the report contends, there will be a “disproportionately rapid evacuation” of people from the tropics. As one of its authors told The New York Times, “in some parts of the world, national borders will become irrelevant. You can set up a wall to try to contain 10,000 and 20,000 and one million people, but not 10 million.”The report provides few truly new insights for those who have been paying attention to the issue. In fact, because the IPCC is such a slave to consensus, and because its slow process means that the most recent science is never included in its reports, this one almost certainly understates the extent of the problem. Its estimates of sea-level rise are on the low end—researchers are increasingly convinced that melting in Greenland and the Antarctic is proceeding much faster than expected—and it downplays fears, bolstered by recent research, that the system of currents bringing warm water to the North Atlantic has begun to break down.* As the chemist Mario Molina, who shared the Nobel Prize in 1995 for discovering the threat posed by chlorofluorocarbon gases to the ozone layer, put it, “the IPCC understates a key risk: that self-reinforcing feedback loops could push the climate system into chaos before we have time to tame our energy system.”
All in all, though, the world continues to owe the IPCC a great debt: scientists have once again shown that they can agree on a broad and workable summary of our peril and deliver it in language that, while clunky, is clear enough that headline writers can make sense of it. (Those who try, anyway. An analysis of the fifty biggest US newspapers showed that only twenty-two of them bothered to put a story about the report on the homepages of their websites.)