ARI SHAPIRO, HOST:

Some impacts of climate change are now irreversible, and countries around the world are not doing enough to protect billions of people from the consequences. That's according to a major new report from the U.N.'s Intergovernmental Panel on Climate Change. Here's how U.N. Secretary General Antonio Guterres described it.

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ANTONIO GUTERRES: Today's IPCC report is an atlas of human suffering and a damning indictment of failed climate leadership.

SHAPIRO: An atlas of human suffering. Brian O'Neill of Pacific Northwest National Lab is one of the hundreds of researchers who wrote the report. He says it's easy for scientists to see the fingerprints of climate change on hazards like heat waves, but it's been difficult to blame climate change for the consequences - the resulting death and destruction. That's changing now.

BRIAN O'NEILL: There's one study that finds about a third of heat-related mortality, you know, during summer months over the last few decades globally are attributable to climate change. So we're seeing impacts from climate change increasingly occurring now. This is not just an issue for risks that we will face in the future.

SHAPIRO: Let's talk about how bad this may get because the Earth has already warmed about 1 degree Celsius over preindustrial levels. And scientists and policymakers keep talking about the importance of limiting warming to just 1.5 degrees. But the Biden administration's outgoing deputy climate envoy, Jonathan Pershing, told me in a recent interview that 1.5 is remarkably difficult. Do you agree with that?

O'NEILL: I do. I think that's a conclusion - basically kind of the conventional wisdom from the literature. That effort to understand what it would take to limit climate to 1.5 degrees or 2 degrees is really the focus of the next IPCC report that'll come out in about a month. But certainly from the existing science on this topic, I guess, a broad conclusion will be it appears technically possible but extremely difficult.

SHAPIRO: And what does that mean for the forecast of consequences?

O'NEILL: That we can hope and that we might limit climate to a level like 1.5 degrees, but we should be prepared for more warming than that. If you look at the kinds of impacts that are projected, we could have tens or hundreds of millions of additional people in poverty due to climate change than we would if we weren't experiencing that climate change. The numbers - similar numbers of people could be pushed into food-insecure situations and increase the risk of hunger and malnutrition. Same thing for our coastal areas - that the projected damages to people, to buildings, to infrastructure that are located in low-lying areas close to the coast - those are high. I think we need to keep in mind, though, at the same time that not for all of these outcomes, but for quite a number of them, we are in the middle of decades of progress, according to these measures, and we expect that progress to continue.

SHAPIRO: Well, let's talk about what countries can do to protect those most vulnerable people, particularly because some of these impacts are irreversible. What do countries around the world need to do to insulate people from the effects of climate change that are going to happen no matter what?

O'NEILL: Well, I think one thing that is new in our understanding is that we've got a lot more evidence and can more confidently conclude that while reducing emissions and undertaking very climate-specific adaptations - you know, like, building coastal defenses, things like that to sea level rise - that those are important, and we can do that. But we understand a lot better now that improving living conditions in terms of strengthening our education systems, health systems, making sure our governance works well, that we can make decisions and carry them out effectively and cooperate, whether it's inside a country or between countries - that all of these things are really important to determining how big the risks get in the future. And not in a secondary way. These are just as important in many cases as exactly how much climate we get. So anything we can do to improve those kinds of conditions is also going to improve our resilience to climate change.

SHAPIRO: That's Brian O'Neill, one of the hundreds of authors who helped write the new U.N. report on climate change. Thank you for speaking with us.

O'NEILL: Thank you. Transcript provided by NPR, Copyright NPR.