EPA Administrator Andrew Wheeler says the use of an inappropriately pessimistic climate modeling tool is driving bad press around climate change, and he’s pledged to halt its use.

While he was still acting EPA chief, Wheeler blamed overly dire assumptions for the National Climate Assessment, released by the Trump administration last Black Friday—a launch that seemed calculated to bury the congressionally mandated report, which highlighted the findings of experts at 13 federal agencies that harmful man-made climate change is underway and growing worse.

And Wheeler used a summit last month in Metz, France, with ministers from six principal foreign allies to promise to “reexamine comprehensive modeling that best reflects the actual state of climate science.”

Then, last Monday at a National Press Club briefing, Wheeler lamented that most press coverage of the NCA focused on what he called “the worst-case scenario.”

“I do think we should take a more realistic look at the worst-case scenarios ... all the scenarios ... going forward,” he said.

The “worst-case scenario” Wheeler seems concerned about is something called Representative Concentration Pathway, or RCP, 8.5—a scenario long used by the U.N. Intergovernmental Panel on Climate Change, federal agencies responsible for the NCA, and the climate modeling community writ large to represent the upper extreme of greenhouse gas concentrations that could exist in the world’s atmosphere by the end of this century.

RCP 8.5 assumes the world will curb fossil fuel use by only about 20% over the next 80 years while experiencing relatively low income growth and very high growth in population and global energy demand.

Developed by researchers in Austria in 2007, RCP 8.5 is used by the IPCC and other entities together with three other baseline scenarios that incorporate more optimistic assumptions for global economic development, technology, trade and other factors that could inform future atmospheric greenhouse gas concentrations and, by extension, warming. The IPCC and NCA don’t rely on one scenario for any one report but show a range. The scenarios don’t seek to predict future climate policies but instead focus on longer-term trends.

“We’re not fortune tellers; we’re scientists,” said Richard Moss, a senior scientist doing climate modeling work at the Pacific Northwest National Laboratory’s Joint Global Change Research Institute and a participant in the NCA.

The four scenarios don’t translate precisely to specific degrees of temperature rise—experts note uncertainty about feedback loops and other variables. But an RCP 8.5 pathway could usher in a catastrophic level of warming equal to about 4 or 5 degrees Celsius above preindustrial levels. It’s those findings that triggered some of the headlines Wheeler objected to last week.

EPA seems to be building a case for exiling this “worst-case scenario” from future climate reports by the U.S. government. Sir Robert Watson, a British chemist who briefed Wheeler and his foreign counterparts at Metz last month on the U.N. species extinction report he’d spearheaded, said the EPA administrator singled out RCP 8.5 for criticism in his remarks there, calling the scenario “extreme.”

EPA did not respond to an E&E News query about whether the “worst-case scenario” Wheeler referenced at the press club was RCP 8.5.

But spokesman James Hewitt asserted in a statement that “the previous use of inaccurate modeling that focuses on worst-case emission scenarios, that does not reflect real-world conditions, needs to be thoroughly re-examined and tested if such information is going to serve as the scientific foundation of nationwide decision-making now and in the future.”

“The fundamental problem with worst-case emission scenarios is that they are based on the flawed supposition that the significantly positive trends in global poverty reduction, economic improvement, and demographics could actually slide backwards,” he said.

But experts in climate modeling, including some like Moss, who participated in the NCA, say that while RCP 8.5 represents the more pessimistic end of the report’s range, it isn’t actually extreme. It represents about the 90th percentile of what scientists think could happen this century in terms of greenhouse gas concentrations, which means there’s a 10% chance it’s an underestimate.

And with Brazil, Australia and the United States rolling back climate policies and emissions ticking upward, it’s currently more in line with global emissions than the more-optimistic baseline scenarios.

“We are right on 8.5 right now,” said Don Wuebbles, a professor of atmospheric science at the University of Illinois, Urbana-Champaign, who participated in the NCA. “We are on emissions that are higher than any of the other scenarios right now.”

The Global Change Research Act of 1990, which was signed by President George H.W. Bush and mandated the periodic release of the NCA, was intended to furnish Congress with information to aid with planning, Moss said, not reassurance.

“The whole point of something like this is to prepare for the future, and I’ve never heard of effective risk analysis that picks a low scenario and says, ‘Let’s work from that,’” he said. “This is facetious, but if the planners of D-Day had said, ‘Let’s pick a scenario where the Germans see us coming and lay down their weapons and run away, and let’s plan for that,’ that’s not exactly going to get us on the beach.”

Last week, Wheeler said that the IPCC was “moving away” from using RCP 8.5 in its assessments, but EPA did not respond to E&E News requests to elaborate.

Last year’s landmark IPCC report referenced RCP 8.5, but the purpose of that special assessment was to show the difference between a temperature rise of 1.5 C and 2 C. Since RCP 8.5 correlates to at least twice 2 C, it played a less central role in the analysis than did more optimistic scenarios.

Wheeler also blamed the “Obama White House” for setting the parameters of the NCA, including what he called its “focus” on “the worst-case scenario.”

“I thought that was political interference by the Obama White House in that process,” he told his press club audience.

When asked, EPA’s press office supplied a May 2015 memo from the Subcommittee on Global Change Research of the National Science and Technology Council’s Committee on Environment, which EPA said reflected Obama White House political policies.

But Wuebbles said it reflected consensus among experts at the federal agencies and tracked with the IPCC and previous NCAs. The memo doesn’t set RCP 8.5 as the only scenario to be used—it sets a range of RCP 4.5, a moderate scenario, to RCP 8.5, with some analysis of other baseline scenarios.

Peter Frumhoff, director of science and policy for the Union of Concerned Scientists, said it was ironic that Wheeler was advocating the use of assumptions that track with a quick global shift away from fossil fuels even as he presides over efforts to keep that shift from occurring.

“Mr. Wheeler’s and this administration’s policies to expand fossil fuels use is only increasing the prospect that we’re going to continue to hug that scenario for some time to come until we come out our senses,” he said. “But there’s no evidence in the trajectory that we’re experiencing today that that bending is taking place.”

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news atwww.eenews.net.