Scientists: Global Warming Likely to Surpass 2°C Target

Look a long time for nations to set a speed limit on the road to a warming world.

But for the past four years, even though negotiators have never arrived at a plan for avoiding dangerous climate change, they have agreed on a goal: limiting the increase in the Earth’s global average surface temperature to 2°C (3.6°F) above the preindustrial level.
Now, two Union of Concerned Scientists (UCS) climate scientists and two colleagues argue that policymakers need to acknowledge that the world is already on track for warming beyond 2°C.
“A policy narrative that continues to frame this target as the sole metric of success or failure to constrain climate change risk is now itself becoming dangerous,” wrote Todd Sanford and Peter Frumhoff of UCS in the commentary published Wednesday in Nature Climate Change. “[It] ill-prepares society to confront and manage the risks of a world that is increasingly likely to experience warming well in excess of 2°C this century,” said the piece, co-authored by Amy Luers of the San Francisco-based Skoll Global Threats Fund, and Jay Gulledge, of the U.S. Department of Energy’s Oak Ridge National Laboratory.
Rethinking the Target
The authors are by no means the first to suggest a rethinking of the 2°C goal. Todd Stern, the lead U.S. climate negotiator in President Barack Obama’s administration, provoked anger in 2012 when he said a more “flexible, evolving” approach might be more effective in spurring a political accord. Coming at the issue from an entirely different angle, retired NASA climate scientist James Hansen and a group of colleagues wrote in December the 2°C target was not stringent enough, and “so dangerous” as to be “foolhardy.” At that level, the world risked initiating feedbacks in the climate system, such as the melting of ice sheet area, that could trigger irreversible warming out of humanity’s control.
Hansen and colleagues suggested a 1°C target was far less dangerous. The Earth has warmed 0.85°C from 1880 (preindustrial times) to 2012, according to the latest consensus science reported in September by the Intergovernmental Panel on Climate Change (IPCC), the scientific body established by the United Nations to inform governments of climate risks.
The UCS scientists and colleagues took the IPCC to task for issuing reports that present different future scenarios, while making no judgment on the relative likelihood of the varying projections, “implicitly treating all scenarios as equivalently plausible.”
“Inadvertently, the [IPCC] reinforces the present narrative by failing to provide policymakers with guidance on how to weigh the relative likelihood of the scenarios of future concentrations of heat-trapping gases and other drivers of warming on which its climate change projections are based,” the authors said.
In an email, Rajendra Pachauri, who has been chairperson of the IPCC since 2002 and who is an adviser to National Geographic’s Great Energy Challenge initiative, declined to comment on the opinion piece. “The Panel has an established process for producing its reports and in every respect we make efforts to see that our reports are policy-relevant,” he added.
Gavin Schmidt, a climate scientist with the NASA Goddard Institute for Space Studies, agreed that the world needs to assess the risks of high-magnitude warming, but he said criticism of the IPCC is misplaced.
“We do need to assess the risks of high scenarios, not just assume that [2°C] guiderail is achievable, but the call for IPCC to give probabilistic information about different [scenarios] is just a non-starter,” Schmidt said in an email. “What is the probability of an international carbon tax? A breakthrough in nuclear power generation? Solar? Of missing feedbacks in models becoming important? These are undefinable, and yet essential for what they are calling for.