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2023 was the hottest year on record – by a large margin

ARI SHAPIRO, HOST:

It's official. 2023 was the hottest year ever recorded by a lot. That's according to new data released today by European Union scientists. Rebecca Hersher of NPR's climate desk is here with more. Hi, Becky.

REBECCA HERSHER, BYLINE: Hi.

SHAPIRO: I feel like a Borscht Belt comedian asking you, how hot was it?

HERSHER: (Laughter) So hot, Ari. 2023 was the hottest year since we started keeping track of global temperatures. Reliable records actually go back all the way to 1850, and it was likely the hottest year going back much further than that - like 125,000 years. Scientists can figure that out by, like, looking at rocks and soil to figure out what the climate was like in deeper - in the deeper past, you know, deeper time. And it was the hottest year by a lot, I should say. Like, it blew the previous record out of the water by two-tenths of a degree Celsius, which is about four-tenths of a degree Fahrenheit. It's a huge margin.

SHAPIRO: Describe why two-tenths of a degree Celsius, which doesn't sound like a whole lot, is a huge margin.

HERSHER: Right, right. So the Earth is really sensitive to temperature changes. And one way I like to think about it is it's sort of like the human body. Like, if your body temperature goes up even a couple degrees, you go from healthy to having a fever...

SHAPIRO: Yeah.

HERSHER: ...Being sick. The Earth is similar. So tenths of a degree, they add up really quickly. And this new data, it shows that 2023 was almost 1.5 degrees Celsius hotter than temperatures in the late 1800s. That's, you know, when humans started releasing a lot of greenhouse gases into the atmosphere. One-point-five degrees Celsius, that is more than 2.5 degrees Fahrenheit. And the planet is showing those sort of signs of fever, of being too hot with deadly heat waves and other extreme weather.

SHAPIRO: One-point-five degrees Celsius is a really important number because, people might remember, under the Paris Climate Agreement, the world agreed to try to stay under that number to avoid the worst effects of climate change. Are you saying we're on the cusp of hitting or have already hit that limit?

HERSHER: No. Sort of no. I wish it was a more emphatic no. So hitting 1.5 degrees in one year is not the same as crossing that threshold in a sustained way. That's the good news. You know, like, multiple years in a row at 1.5 degrees, that kind of sustained warming is what's really dangerous. Warming at that level would cause runaway sea level rise and mass extinction of plants and animals later this century - those really catastrophic events. We are not there yet, but scientists warn that we are on track to get there, to hit that kind of sustained warming in the next decade if we don't rapidly reduce greenhouse gas emissions, you know, by burning way less oil, gas and coal.

SHAPIRO: And so now we're in 2024. Is that likely to be another record-breaking year?

HERSHER: It could be. It could be. It's a definite possibility. Some of the ocean heat that helped drive the record-breaking heat last year is still happening, at least in the first part of this year. But, you know, what really matters more than one hot year or even two hot years is the bigger trend, right? So zoom out. The last eight years were the hottest eight years on record. The next eight years are going to be even hotter. You know, another way to think about this is that 2023 was the hottest year that anyone alive has experienced. But if the Earth keeps warming at this rate, we'll look back on 2023 as one of the coolest years that we ever lived through.

SHAPIRO: NPR's Rebecca Hersher, thank you.

HERSHER: Thanks.

(SOUNDBITE OF SINY'S "ORANGE") Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

Rebecca Hersher (she/her) is a reporter on NPR's Science Desk, where she reports on outbreaks, natural disasters, and environmental and health research. Since coming to NPR in 2011, she has covered the Ebola outbreak in West Africa, embedded with the Afghan army after the American combat mission ended, and reported on floods and hurricanes in the U.S. She's also reported on research about puppies. Before her work on the Science Desk, she was a producer for NPR's Weekend All Things Considered in Los Angeles.