A scientist and author of the 1,600-page climate change report quietly released last Friday is debunking claims made by President Donald Trump who declared he’d “read some of” the report before saying, “I don’t believe it.”

The second volume of the fourth National Climate Assessment is the US government’s “State of the Union” on climate change. Every four years, Congress mandates the Global Change Research Program—made law under the Global Change Research Act enacted in 1990 by President George H.W. Bush—to submit interagency findings on current and long-term climate issues to the president and Congress.

In essence, it predicts how America’s future will be shaped by sea level rise, worsening air quality, drought, and other consequences of humanity’s impact on Earth.

On Tuesday, atmospheric scientist Katharine Hayhoe, who co-wrote the report and leads the Climate Science Center at Texas Tech University, addressed some of the president’s claims.

White House spokesperson Lindsay Walters responded to the report on Friday, alleging that it was “largely based on the most extreme scenario.”

Interior Secretary Ryan Zinke echoed this claim. In an interview with Sacramento TV station KCRA on Tuesday, Zinke said, “It appears they took the worst scenarios and they built predictions on that.”

But the report describes several climate change models used to make projections, and it’s unclear how the Trump administration arrived at this conclusion.

“I wrote the climate scenarios chapter myself so I can confirm it considers ALL scenarios, from those where we go carbon negative before end of century to those where carbon emissions continue to rise,” Hayhoe tweeted. “What WH says is demonstrably false.”

According to one of the report’s chapters, some of the scenarios were based on an increasing dependence on fossil fuels, while others were based on reduced emissions. “The resulting range in forcing scenarios reflects the uncertainty inherent in quantifying human activities and their influence on climate,” it states.

The White House also said that future climate assessments will “provide for a more transparent and data-driven process that includes fuller information on the range of potential scenarios and outcomes.”

The report was vetted by 13 federal agencies and based on peer-reviewed literature, according to one agency, the National Oceanic and Atmospheric Association (NOAA).

And as Hayhoe noted, each section was “fully documented by a ‘traceable account’ that contains full citations, sources, references, and documentation supporting that key message.”

For example, the traceable accounts describe in detail how each chapter was authored. Several chapters, such as those on air quality and coastal effects, were compiled by all-federal employee teams, while others—the one on Indigenous livelihoods and economies, for example—solicited input from key stakeholders such as tribal partners.

Another common refrain was that money and political interests shaped the report. “If there was no climate change, we’d have a lot of scientists looking for work,” Rick Santorum claimed on CNN on Sunday.

Former Republican congressman Tom DeLay made a similar claim the following day, telling CNN the report was “nothing more than a rehash of age-old 10 to 20 year assumptions made by scientists that get paid to further the politics of global warming.”

But as Hayhoe pointed out, recent data—rainfall measurements from hurricanes Harvey and Maria, for example—was used to inform the report’s conclusions.