Environmental Protection Agency head Scott Pruitt suggests that global warming isn’t necessarily “a bad thing” because “humans have most flourished during times of … warming.” But recent years have been the warmest humans have seen over at least the last millennium. This record warmth is tied to more extreme weather events, sea level rise and other negative impacts.

Pruitt made his claim on Feb. 6 while speaking with Gerard Ramalho of NBC News 3 in Las Vegas (starting at 4:08).

Ramalho, Feb. 6: People don’t seem to dispute the fact that the climate is changing, but there are two areas that are disputed and I’d love to get your thoughts. One is, is man causing the climate to change? And the other area is should we be alarmed because we hear about things like the polar caps melting and oceans rising and hurricanes and tornadoes that are more intense. What are your thoughts on this? Pruitt: I think that’s well said. I think that you’re right that no one disputes the climate changes, is changing. We see that that’s constant. We obviously contribute to it. We live in the climate, right? So our activity contributes to the climate changing to a certain degree. Now measuring that with precision is, Gerard, I think is more challenging than is let on at times. But I think the bigger question is what you asked at the very end — is it an existential threat? Is it something that is unsustainable? Or what kind of effect or harm is this going to have? We know that humans have most flourished during times of, what? Warming trends. And so, I think there’s assumptions made that because the climate is warming that that necessarily is a bad thing.

We reached out to Pruitt’s office for support for his claims, but spokeswoman Liz Bowman didn’t provide us with any.

Pruitt is right that human civilization began flourishing during a warm period after the last major ice age, which ended about 12,000 years ago. This period — the Holocene Epoch — averaged about 4 to 5 degrees Celsius above the temperatures during the ice age that came before it, Andrew Glikson, an earth and paleo-climate scientist at Australian National University, told us via email.

But the burning of fossil fuels has pushed this global average even higher. Some scientists, including Glikson, even say this new warming trend deserves to be designated as an entirely new epoch — the Anthropocene.

The planet has warmed nearly 1 degree Celsius already since 1880, according to NASA. “Multiple paleoclimatic studies indicate that recent years are all the warmest, on a global basis, of at least the last 1,000 years,” says the National Oceanic and Atmospheric Administration.

How much warming we see in the future depends on how much action we take to reduce greenhouse gas emissions.

For example, if countries fulfill their pledges under the Paris Agreement, but make no further commitments to reducing emissions, the climate modeling nonprofit Climate Interactive found that the planet would see roughly 3.3 C of warming above pre-industrial levels by 2100, though that number could be as high as 4.4 C or as low as 1.9 C.

We’ve outlined some of the impacts of recent warming in previous articles.

In an article we published after Hurricane Harvey hit the U.S. with record amounts of rain last August, we explained that human activities have contributed to the increase in hurricane activity in the North Atlantic Ocean since the 1970s. We also pointed out that the Atlantic Ocean is projected to see increases in hurricane precipitation in the future.

In October, we explained that global warming can bring about conditions, such as heat and drought, that make wildfires more likely to occur and spread. “Climate change plays a role in increasing the rate at which vegetation dries out and becomes receptive to igniting and carrying fire,” one expert told us.

Scientists also have high confidence global warming will lead to more heat waves, we pointed out last March. For example, Washington, D.C., is expected to see 60 to 70 days a year on average reaching 90 degrees Fahrenheit between 2041 and 2070, compared with 20 to 30 days above 90 F between 1971 and 2000 — and that’s for the lower emissions scenario.

In that same article, we explained that sea level already has risen about 8 inches since 1880. By 2100, scientists expect it to rise 1 foot to 4 feet. Coastal communities are particularly threatened by sea level rise. For example, New Orleans, Miami, Tampa, Charleston and Virginia Beach are among those most at risk, according to scientists.

Last August, we explained that increased carbon dioxide in the atmosphere, which drives global warming, likely will have a net negative impact on agriculture. An atmosphere with more CO2 does boost crop yield in the short term via increased rates of photosynthesis. But in the long term, multiple experts told us the positive effect of increased CO2 on crops will diminish, and the negative impacts of climate change, such as higher temperatures and extreme rainfall, will grow.

The warming the planet has seen over the past decades also has “significant potential” to lead to “unanticipated changes” in the Earth’s climate, says the 2017 report by the U.S. Global Change Research Program, a collaboration of 13 government agencies. These “surprises” can come about when multiple extreme events co-occur, such as heat and drought, the report explains. The more we warm the planet the higher likelihood these unpredictable events will take place, the report adds.

This is important, given the fact that human civilization progressed into what it is today, in large part, because the Earth’s climate remained relatively stable during the Holocene.

In fact, the United Nations Intergovernmental Panel on Climate Change says that “the Holocene appears by far the longest warm stable period … over the last [400,000 years], with profound implications for the development of civilisation.”

A stable climate allowed for the development of agriculture, which ensured a reliable food source, explains NASA. It also allowed humans to “domesticate animals, settle down and develop culture,” NASA adds.

But there were some changes in climate during the Holocene, some of which played a role in the collapse of civilizations. Scientists have linked drought, for example, to the demise of ancient Egyptian, Mayan and Cambodian civilizations, says NASA.

“When we excavate the remains of past civilizations, we rarely find any evidence that they made any attempts to adapt in the face of a changing climate,” Jason Ur, a professor of anthropology at Harvard University, told NASA. “I view this inflexibility as the real reason for collapse.”

In an email to us, Ur put it this way: “Human societies have sometimes survived warming trends, but rarely unscathed.”