Excerpt from Chris Mooney in WaPo, March 2018
What’s most striking is the radical nature and rapidity of the changes that would be required to somehow preserve a world below 1.5 degrees.
The document finds that the world has 12 to 16 years’ worth of greenhouse gas emissions left, from the start of 2016, if it wants a better-than-even chance of holding warming below 1.5 degrees. Two of those years have already elapsed, as of this writing. A third will have nearly elapsed by the time the draft report is finalized and released in October. (In December in Poland, it will feed into a broader United Nations deliberation about the adequacy of countries’ current promises to cut emissions.)
And once this “carbon budget” for 1.5 degrees Celsius is used up, emissions would have to plunge to zero to preserve the 1.5 degree goal — something that would almost certainly never happen, as it would sharply impair the world economy.
Since such rapid and severe cuts aren’t likely, the report notes that it’s virtually unavoidable that the planet will “overshoot” 1.5 degrees Celsius. To cool Earth afterward and avoid staying at dangerously high temperatures for long, it would then be necessary to remove carbon dioxide from the air at a massive scale — but that, too, is highly problematic.
Carbon removal scenarios generally involve reforesting large amounts of land, or growing trees or other plants on that land and using it for energy, and storing the resulting carbon dioxide emissions underground. But “increased biomass production and use has the potential to increase pressure on land and water resources, food production, biodiversity, and to affect air quality,” the draft notes. “Therefore, the scale and speed of implementation assumed in some 1.5 C pathways may be challenging.”
“Avoiding a 1.5 C warming would be very, very difficult without a significant overshoot,” said Princeton University climate scientist Michael Oppenheimer, noting that he was commenting solely on the state of the science itself, rather than the leaked document. “Such a warming would cause increased bleaching and perhaps destruction of living coral reefs at some locations, although at other places, reefs would probably survive a warming closer to 2 C.”
“Some of the high level messages I think come as no surprise, in that we are not on track anywhere near toward 1.5 C, and getting there would require enormous changes,” added Shindell, noting that he was not speaking as an author of the draft report or on behalf of the IPCC, but simply as a scientist with expertise in the matter. “That basic conclusion, I think it’s okay to say that it’s not a surprise to anybody. Any climate scientist would have told you that even without the report.”
The document’s leak has become a standard affair for major United Nations climate science reports, because they are seen by so many reviewers.
In 2013, a leaked draft of part of the Intergovernmental Panel on Climate Change’s fifth assessment report helped lend credence to the questionable idea that global warming had slowed or “paused,” based on a brief passage suggesting that the rate of warming had declined somewhat between 1998 and 2012. The final draft addressed the issue with more nuance, largely undermining the notion of any significant slowdown.
The authors have until May 15 to include any new published material in the report. Still, it’s unlikely to change the fundamental conclusion that there is too little time to avert 1.5 C degrees of warming — barring some massive technological intervention.
“There is … no documented precedent for the geographical and economic scale of the energy, land, urban and industrial transitions implicit in pathways consistent with a 1.5 C warmer world,” the draft report notes