Floodwater surrounds a home after torrential rains pounded Southeast Texas following Hurricane and Tropical Storm Harvey, causing widespread flooding, on September 3th, 2017, in Orange, Texas. New data finds that climate change likely increased the rainfall during Harvey by 38 percent. (Photo: Scott Olson/Getty Images)

Typically, the presentations at scientific meetings can feel a bit esoteric for the non-scientists in the room. But at an enormous meeting for Earth and space scientists on Tuesday, in Washington, D.C., some presenters had quite simple messages.

"The bottom line is: Climate change is real. It is us. And it is serious," Katharine Hayhoe, a climate scientist at Texas Tech University, said in a pre-recorded message.

"The first key message is similar to previous national assessments and international assessments: Climate change is affecting the health of Americans," Kristie Ebi, a public-health researcher from the University of Washington, said at the beginning of her talk.

Scientists have long known that climate change is real, human-caused, and could harm human health, so it's striking to hear them say so during an event that's supposedly for other professionals already well-versed in the research. "It's a little more in your face," says Michael Wehner, a climate change analyst for the Lawrence Berkeley National Laboratory. "That's by design."

Not only is the science clearer now than it's ever been, it's also being debated in an unprecedented way.

Wehner, Ebi, and Hayhoe all worked on the Fourth National Climate Assessment, a report on the state of climate change's effects on America, which a 1990 law requires that scientists submit every four years. The latest report is the first, however, to be published during the Trump administration, which has taken an unusual approach to climate science. Even past presidents, who have not been inclined to enact climate-saving policy, at least paid lip service to the scientific consensus. President Donald Trump has said he doesn't believe the report and his administration has proposed numerous steps that would worsen the United States' Earth-warming emissions.

The report was supposed to have debuted here, at the fall meeting of the American Geophysical Union, which more than 25,000 people were expected to attend. But, in a surprise decision, the government decided to publish it on the Friday after Thanksgiving, when many Americans were enjoying a holiday, as The Atlantic reports. The timing was designed to minimize the impact of the report's ever surer and starker warnings about climate change, anonymous sources told the New York Times.

Still, the room was full for Hayhoe, Ebi, and others' presentations on highlights from the report. They talked about what's new in the report, compared to the previous assessment, published in 2014. One important advance? Scientists' ability to say climate change has caused excess flooding during a storm, or deaths during a heat wave.

"Don't ever say again—because people used to say this and it used to be correct—that scientists won't say anything about individual events, but it fits with expectations. That's no longer true," Wehner says. "We say lots and lots about individual events." Wehner is presenting research at this meeting that finds that climate change likely increased the rainfall during Hurricane Harvey by 38 percent.

Ebi, who worked on the human health chapter of the assessment, said: "The thing that's changed is that there's now detection and attribution studies for health, showing, in fact, that people are suffering and dying from climate change, right now."

The science on climate change's ill effects is stronger now not just because scientists have improved their methods, but because the effects are more obvious and show up more clearly in the data, Wehner says: "All this is easier than it used to be because the situation is worse than it used to be. It's warmer and things have changed more."