As if parading its best evidence against an expected onslaught of climate denial, the Obama Administration released on Thursday an updated compendium of the accepted science about global warming.
The science review is intended to guide the preparation of the government's next National Climate Assessment, a periodic comprehensive report scheduled to be released in in 2018. The last assessment was published in 2014.
With the entire Obama climate agenda expected to come under assault by the Donald Trump regime, this report, released in draft form for comment by experts, lays down a marker for the climate consensus. It may well become a benchmark against which the next administration will be measured.
It is not just a map of the known climate science. It is also a political chessboard on which a high-stakes tug of war over science, energy policy and ideology may play out in the months ahead.
"This report is a comprehensive and updated assessment of the state of knowledge on human-induced climate change," the White House said as it announced the draft, "including observed and future projected changes in temperatures, precipitation patterns, extreme-weather events, sea-level rise, and ocean acidification, focused primarily on the United States."
The Climate Science Special Report was produced by the U.S. Global Change Research Program, the interagency coordinating body for all federal climate research. Forty-four scientists from federal agencies, laboratories and universities helped write the draft. It is still under peer review through the National Academies of Sciences.
At the most basic level, the report speaks bluntly of the core understanding of climate science that is accepted by essentially every authoritative institution, yet remains anathema to some politicians.
"Human activities, especially emissions of greenhouse gases, are primarily responsible for observed climate changes in the industrial era," it says. "There are no alternative explanations."
But its more significant contribution comes in its presentation of the peer-reviewed science published during the past few years, a time when global warming has seemed to lurch into overdrive.
Among the salient updates is the report's detailed discussion of the putative "hiatus," or unexpected pause in global warming after the intense 1997-98 El Niño spike in temperatures. The hiatus notion, often seized upon by those disputing the consensus on climate change, has essentially been laid to rest in the past couple of years. Additional research fleshed out the scientific picture, just as the latest El Niño came and went with an even higher temperature spike.
The report concludes that "surface and tropospheric temperature records do not support the assertion that long-term global warming ceased, a conclusion further reinforced by recently updated and improved datasets."
In another important advance, the report's final chapter, called Potential Surprises, gives the first thorough look of any national climate assessment at the problem of "tipping points," or "perfect storms." These are events that may lurk outside the edges of inherently imperfect climate models.
"Humanity is conducting an unprecedented experiment with the Earth's climate system," it declares. "There is a significant potential for our planetary experiment to result in unanticipated surprises, and a broad consensus that the further and the faster the Earth's climate system is pushed towards warming, the greater the risk of such surprises."
The draft's 533 heavily annotated and illustrated pages encapsulate what's new and different in the increasingly robust scientific consensus. It shows which models are improving and how, and which observations are more illuminating and why.
It notes "significant advances" in the reliability with which scientists can link individual extreme events—heat waves, for example—to manmade climate change.
It contains extensive new research on ocean acidification, warming and oxygen loss—all potentially profound consequences of the addition of carbon dioxide to the atmosphere. Further, it presents "growing evidence" that an important oceanic circulation described in layman's terms as the ocean's conveyor belt may be slowing.
It also updates the worrisome trends—which just in recent weeks have been seizing headlines again—in the loss of ice sheets and sea ice in both the Arctic and Antarctic regions.
In the near term, many ill effects are already locked in by pollution that has been emitted so far. The worst effects of continuing business as usual for another decade will pile up as more time goes by.
In short, the worst effects already being felt will become the new normal before long.
"The temperatures of recent record-setting years will become relatively common in the near future," with temperatures expected to rise in the next few decades even if emissions of greenhouse gases are significantly reduced. Temperatures in the U.S. are likely to keep going up for the rest of the century, it says.