Current national commitments to cut greenhouse gases would likely allow average global temperatures to rise by 3.5°C by 2100, suggest new modeling results released today. That is well above the 2°C rise deemed safe by many policymakers and researchers.
The analysis, appearing roughly 2 months ahead of a United Nations meeting in Paris intended to finalize a new global climate deal, focuses on the emissions levels that nations have already pledged to reach by 2025 to 2030. These are officially known as Intended Nationally Determined Contributions, or INDCs. So far, about 72 nations responsible for roughly 65% of the world’s emissions have submitted INDCs. (More than 190 nations may eventually participate.) The 72 include many of the world’s largest emitters, including the United States and China. But some larger emitters that haven’t yet submitted INDCs, including India, Iran, Indonesia, Saudi Arabia, South Africa, Thailand, Turkey, Ukraine, and Pakistan. (Brazil, another relatively large emitter, just released its INDC on 27 September.)
The new modeling, conducted by the Washington, D.C.–based nonprofit group Climate Interactive, assumes annual emissions will remain flat for the remainder of the century after 2025 to 2030; nations will neither do more to clamp down on annual emissions, nor allow them to rise. That would translate to steadily rising temperatures as carbon pollution continues to accumulate in the atmosphere (see red curve below), and fail to reach the goal of holding warming to 2°C (blue curve at bottom).
“The commitments thus far get us on the pathway, but they don’t get us where we need to be,” says John Sterman, an economic modeler who focuses on climate at the Massachusetts Institute of Technology in Cambridge. “More aggressive reductions are needed.”
The modeling also highlights that, under this scenario, developing nations will produce a big portion of global annual emissions in the future. Overall, China, India, and other developing nations will account for about 80% of total global emissions by 2100, the scenario suggests, and the United States and European nations will account for less than 20%.
The analysis follows previous studies that show that a business-as-usual scenario, which assumes a continued growth of global emissions, would deliver a warming increase of 4.5°C by 2100. So the projection that current national commitments would prevent nearly a full degree of warming by 2100 is an important accomplishment, says Andrew Jones, Climate Interactive’s co-director. But making further progress, he says, will require both actions to make good on current INDCs, which are just pledges, and moves to set even more aggressive goals later. “The big question is what happens after 2030,” he says.
Climate Interactive is just one of three major groups that undertake climate emissions score-keeping. The United Nations Environment Programme’s annual Emissions Gap Report, expected in November, includes commitments both on mitigation and adaptation. And the Climate Action Tracker, run by European academics, rates the strength of nations’ contributions. (It has rated the United States and China pledges as “medium,” for example, because they would rely on other contributions to maintain warming at 2°C. It judges that only two nations have submitted “sufficient” pledges—Ethiopia and Morocco—and none have submitted “role model” INDCs.)
Climate Interactive, meanwhile, wants to enable people to follow INDCs—and their potential impact on warming—in near real-time. It is offering computer and cellphone users embeddable applications that automatically update as nations submit or alter their commitments.