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%.