Landmark Agreement on Climate Is Reached in Paris to Cap Warming

Climate negotiators meeting here in Paris have achieved a deal that could change the world.  Conference chair and French foreign minister Laurent Fabius crowed that he had presided over a "historical turning point."  Even when the hype has died down, that may turn out to be true. Even climate scientists who on Friday had sharply criticized an earlier draft of the text were convinced. 

The Paris Agreement commits the world to capping global warming to "well below 2 degrees Celsius above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 degrees C."  To achieve that, it requires the world to "reach global peaking of greenhouse gas emissions as soon as possible" and  "to undertake rapid reductions thereafter, in accordance with best available science."

The intention is to reduce net greenhouse gas emissions to zero "in the second half of this century."  That is, any emissions would have to be balanced by uptake by nature or some future technology for soaking up greenhouse gases from the atmosphere. 

"This agreement is a turning point," said Johan Rockstrom, director of the Stockholm Resilience Center and architect of the science that looks at "planetary boundaries" within which society may safely work. 

The day before the final deal was done, climate scientists here had ripped into a penultimate draft, saying its temperature aspirations were admirable, but were made meaningless because they were not matched by mechanisms for reaching them.  "Diplomats understand the economics, but not the science," said Kevin Anderson, of Manchester University, England. 

But in the final hours, science was added to the agreement to put some numbers on reaching the aspirations.  It did not bridge the gap between aspirations and pledges, but it shone a light on the gap that had to be filled and offered some opportunities for when it might be narrowed. 

The final version noted that the emissions pledges from the 184 nations that form the heart of this agreement would lead to global emissions of 55 gigatons of greenhouse gases in 2030.  But that, it said, fell far short of the reduction to 40 gigatons a year needed for limiting warming to two degrees.  It added that the even lower levels of emissions necessary to secure 1.5 degrees had yet to be determined. 

The agreement also sets up a U.N. scientific stock-taking of progress on the goals, to be completed in 2018, which is the same time as receipt of a report it has commissioned from the Intergovernmental Panel on Climate Change (IPCC) on the "emissions pathways" needed to meet 1.5. 

"The new text is clearer in scientific terms than what we had before," said Joeri Rogelj of the International Institute for Applied Systems Analysis in Laxenberg, Austria.  "Importantly, the benchmarks in terms of global peaking and global emissions reductions are consistent with the 1.5 degree and two degree temperature targets." 

The agreement may be consistent with science, but scientists here remain wary about what is actually achievable.  In particular, the difference between halting warming at two degrees or 1.5 may sound relatively small.  But 1.5 degrees is twice as hard because only half as much carbon can be emitted from now on – around 500 gigatons.  That is around ten years' emissions at current rates. 

Achieving that is simply beyond the realms of possibility, most researchers that Yale Environment 360 spoke to here believe.  Even to achieve a 50-50 chance of that goal would require annual year-on-year emissions cuts of 15 percent or more, said Anderson. 

While the IPCC has been asked to look again at its analysis of what it would take to achieve 1.5 degrees, the panel actually reported on that in its most recent scientific review last year, said Rogelj.  It concluded then that 1.5 degrees would almost certainly involve initially overshooting the emissions target, followed by finding ways to extract greenhouse gases from the air. 

The most likely method of achieving these "negative emissions" would be burning biomass in power stations and capturing and burying the resulting emissions.  New crops grown in place of the burned biomass would then soak up CO2 from the air. 

John Schellnhuber, director of the Potsdam Institute for Climate Impact Research, said that overshoot "could be tolerated" by the planet, without triggering any likely climatic tipping points, provided it were only for a few decades.  But whether the aim was two degrees, or an overshoot and return to 1.5, every nation should aim to hit zero emissions by 2050, he said. 

That should include emissions from aviation and shipping, which are inexplicably left out of the Paris agreement, said Anderson.  Such gaps make many scientists still cautious about the "historic" agreement.  But they have a second problem, the "bottom-up" process of arriving at emissions targets, and the difficulty of making them compatible with [desired outcomes]. 

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