Global climate is warming rapidly, US draft report warns

BMJ 2017; 358 doi: (Published 09 August 2017) Cite this as: BMJ 2017;358:j3824
  1. Michael McCarthy
  1. Seattle

The global climate is warming rapidly and will continue to do so even if “greenhouse” gas emissions are reduced substantially, US climate experts conclude in a draft report leaked to the New York Times.1

“Recent data adds to the weight of the evidence for rapid global-scale warming, the dominance of human causes, and the expected continuation of increasing temperatures, including more record-setting extremes,” the report says.

The National Academy of Sciences had signed off on the report, which is mandated by Congress to be prepared every four years, but the draft had not yet been approved by the Trump administration. The New York Times said that the researchers had decided to supply the draft to reporters because of concerns that the report may be suppressed by the Trump administration.

Donald Trump has called global warming a “hoax” created by China to make US manufacturing non-competitive, and in June he announced that he was withdrawing the US from the 2016 Paris Agreement, which he said was unfair to the US and would undermine its economy.

In the agreement 195 nations pledged to take voluntary steps to curtail greenhouse emissions, with the goal of limiting the increase in the global average temperature to less than 2°C above pre-industrial levels, ideally limiting this increase to 1.5°C above pre-industrial levels.

Trump has also appointed Scott Pruitt, a climate change skeptic, to lead the US Environmental Protection Agency. Pruitt has argued that the science of climate change is far from settled, and he has led the administration’s efforts to roll back programs instituted by President Barack Obama to limit carbon emissions.

The new draft report, however, finds strong evidence that warming of the global atmosphere and oceans is real, rapidly increasing, and caused by humans, as temperatures have risen more quickly over the past century than at any time in the past 1700 years—the period over which global temperature change can be reconstructed.

The report says that global annual average temperatures increased by more than 1.2°F (0.7°C) from 1986 to 2016, relative to temperatures seen from 1901 to 1960. Over the entire period from 1901 to 2016 the temperature rose by 1.8°F (1.0°C), it says.

In all emission scenarios, the report warns, temperatures in the US are expected to rise over the next few decades by 2.5°F (1.4°C) relative to the recent past (1976-2005). “Recent record-setting years may be ‘common’ in the near future,” it adds.

The magnitude of global warming will depend primarily on the amount of greenhouse gases emitted, the draft report notes. It explains, “With significant reductions in the emissions of greenhouse gases, the global annually averaged temperature rise could be limited to 3.6 degrees F (2.0 degrees C) or less.

“Without major reductions in these emissions, the increase in annual average global temperatures relative to pre-industrial times could reach 9 degrees F (5.0 degrees C) or more by the end of this century.”


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