By Chris Mooney
29 February 2016
(Washington Post) – On Sunday night while accepting a long-anticipated Oscar for best actor, for his role in “The Revenant,” Leonardo DiCaprio seized the moment to highlight the plight of the planet.
“Making “The Revenant” was about man’s relationship to the natural world,” DiCaprio said. “A world that we collectively felt in 2015 as the hottest year in recorded history. Our production needed to move to the southern tip of this planet just to be able to find snow.”
“Climate change is real. It is happening right now,” DiCaprio continued. “It is the most urgent threat facing our entire species, and we need to work collectively together and stop procrastinating.” (You can watch the full speech here.)
A little-noticed scientific study that emerged last week not only bears this out — but it also suggests that climate change could be a more urgent problem than we all assumed.
At least since 2013, it has been common to claim that the world has a limited carbon “budget” to emit if we still want good odds of keeping global warming below 2 degrees Celsius above pre-industrial levels, a widely accepted international target. […]
But in a new study in Nature Climate Change last week, Joeri Rogelj of the International Institute for Applied Systems Analysis in Austria and an international team of colleagues interrogate this notion of a carbon “budget” and provide some reasons for thinking we could actually have even less wiggle room than that.
“We shaved off the higher end of the estimates, and we showed that the lower end of the previous range is actually what we should be aiming at,” Rogelj says.
First of all, the IPCC’s budget numbers were up through 2011 — and the world, Rogeli and his colleagues say, has been emitting about 40 gigatons per year. So already the budget is much narrower.
On top of that, though, Rogelj and his fellow researchers looked at different ways of computing the carbon budget — including different approaches taken by other parts of the IPCC itself that differ from the estimate cited above. “Already in the IPCC, there were many carbon budget estimates that all used different methodologies and showed something different,” Rogelj says.
And for a variety of technical reasons, Rogelj and his team don’t opt for the aforementioned 1,000 gigaton budget as the top choice. Rather, they say, a budget of between 590 and 1,240 gigatons, as of last year, is the “most appropriate” to use, if we want a better than two-thirds chance of keeping global warming below 2 degrees. That translates, the study says, into between 15 to 30 years of emissions at the current rate. […]
“Different estimates of the carbon budget either ignored the climate effects of non-CO2 gases, ignored co-emissions, were based on a smaller sample of emissions scenarios, or used a different threshold of probability for holding warming below 2 degrees C,” explains Climate Analytics, whose director Michiel Schaeffer was one of the co-authors of the new paper.
The prominent figure of 1,000 gigatons — now reduced to about 850 as of 2015, Rogelj says — still lies within the 590 to 1,240 gigaton range. It’s just that the danger zone could be breached with a considerably lower level of emissions, based on this new analysis. And of course, if we want to hold warming to just 1.5 degrees — or, if we want a higher level of certainty than 66 percent — the budget gets even narrower. [more]