The report’s text, which strongly affirms that global warming is being driven by humans, received an overall clean bill of health Tuesday from the academies. The committee of 11 scientists reviewing the report called it “impressive, timely, and generally well-written” and said it was “generally impressed with the breadth, accuracy, and rigor of the draft. The draft emphasizes the robust evidence that human emissions of greenhouse gases (GHGs) have substantially warmed the planet and are causing myriad changes to the Earth system, some of which are effectively irreversible on human timescales.”

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Environmental Protection Agency Administrator Scott Pruitt last week called such findings into question, suggesting that humans are not a “primary contributor” of climate change. Energy Secretary Rick Perry and Interior Secretary Ryan Zinke, in their confirmation hearings, also held back from acknowledging the dominant human causation of climate change. And Trump has done little to reverse his prior climate doubt, telling the New York Times: “It’s a very complex subject. I’m not sure anybody is ever going to really know.”

Andrew Rosenberg, a former National Oceanic and Atmospheric Administration marine scientist who now directs the Center for Science and Democracy at the Union of Concerned Scientists, said this of the draft report: “The reviewers had many recommendations for strengthening the report to make it clearer for technical and non-technical audiences. But, the primary findings clearly past muster.”

“What strikes me is the contrast between this report — what the scientists say — and statements from EPA Administrator Pruitt,” Rosenberg said.

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The key question is what that clash means for the document itself and a broader national climate assessment process that now falls into the hands of a lightly staffed Trump administration that seems bent on reversing Obama administration climate priorities.

“The National Academy of Science’s review of the U.S. Global Change Research Program’s Special Report not surprisingly reaffirms the basic science of climate change,” said Tom Lovejoy, an ecologist at George Mason University. “Indeed every national academy in the world has concluded climate change is real and a serious threat to human well-being.”

The National Climate Assessment process was mandated by Congress in 1990. The next installment of its report — its fourth — is due out next year. The report outlines the fundamental climate science that underlies the broader region-by-region assessment and is designed to feed into its design.

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During the George W. Bush administration, the national assessment was a continual flash point and triggered charges that the administration was leaning on climate science and trying to skew it for political reasons.

During the Trump years, a greater threat could be budget cuts. The Global Change Research Program had a 2016 budget of $2.6 billion, but not standing on its own — that budget refers to contributions from more than 10 federal agencies, many of which are now individually in the crosshairs.

Congressional Republicans have recently criticized the Global Change Research Program and argued that funding “should only be available contingent on a finding by the administration that it is not duplicative or wasteful based on a government-wide review of climate research.”

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Into this cauldron comes the Special Report, which, at least in draft form, contains strong language about the human causation of climate change. In perhaps its most quotable section, it states the following conclusion:

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Many lines of evidence demonstrate that human activities, especially emissions of greenhouse gases, are primarily responsible for the observed climate changes in the industrial era. There are no alternative explanations, and no natural cycles are found in the observational record that can explain the observed changes in climate. (Very high confidence)

That’s not to say such language will appear in the final report — the peer review by the National Academies actually faults this passage in part, calling for its “rewording,” even as it winds up mostly agreeing with it.

“The concept of ‘no alternative explanations’ needs further discussion to be understood by the intended audience,” the review says. “There are lots of alternative explanations. It is just that, for a number of very solid reasons, they are not credible or cannot contribute more than marginally to the observed patterns.”

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A more technical statement of the same basic point found an even stronger blessing from the committee. In its second chapter, the Climate Science Special Report asserts that:

Human activities continue to significantly affect Earth’s climate by altering factors that change its radiative balance (known as a radiative forcing). These factors include greenhouse gases, small airborne particles (aerosols), and the reflectivity of the Earth’s surface. In the industrial era, human activities have been and remain the dominant cause of climate warming and have far exceeded the relatively small net increase due to natural factors, which include changes in energy from the sun and the cooling effect of volcanic eruptions. (Very high confidence).

Of this passage, the peer review committee says: “This finding affirms the scientific consensus that anthropogenic emissions of GHGs have perturbed the radiative balance of the Earth.” It then recommends some relatively small clarifications.

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What happens next is anyone’s guess. At a scientific conference in Boston in February, one expert involved in drafting the report said he had not spoken to the Trump administration.

“The simple answer . . . in terms of leading the Climate Science Special Report,” said Donald Wuebbles, a University of Illinois climate scientist who was one of the three authors that led its drafting, “is that we’ve had no contact.”

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