‘I am more worried than ever’: Scientists explain why record-shattering 2023 heat has them on edge

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The latest calculations from several science agencies showing Earth obliterated global heat records last year may seem scary. But scientists worry that what's behind those numbers could be even worse.

News agency the Associated Press spoke to more than three dozen scientists about what the smashed records mean. Most say they fear acceleration of climate change that is already right at the edge of the 1.5C increase since pre-industrial times that nations had hoped to stay within.

“The heat over the last calendar year was a dramatic message from Mother Nature,” says University of Arizona climate scientist Katharine Jacobs. Scientists say warming air and water is making deadly and costly heatwaves, floods, droughts, storms and wildfires more intense and more likely.

This last year was especially bad.

The climate behaved in strange ways in 2023

Average global temperatures broke the previous record by a little more than 0.15C, a big margin, according to calculations released on Friday by two top American science agencies, the British meteorological service and a private group founded by a climate skeptic.

Several of the scientists who made the calculations said the climate behaved in strange ways in 2023. They wonder whether human-caused climate change and a natural El Nino were augmented by a freak blip or whether “there's something more systematic afoot,” as NASA climate scientist Gavin Schmidt put it - including a much-debated acceleration of warming.

A partial answer may not come until late spring or early summer. That's when a strong El Nino - the cyclical warming of Pacific Ocean waters that affects global weather patterns - is expected to fade away. If ocean temperatures, including deep waters, keep setting records well into the summer, like in 2023, that would be an ominous clue, they say.

Nearly every scientist who responded to AP's questions blamed greenhouse gases from the burning of fossil fuels as the overwhelmingly largest reason the world hit temperatures that human civilisation has not likely seen before. El Nino, which is bordering on 'very strong', is the second-biggest factor, with other conditions far behind, they say.

The trouble with 2023, NASA's Schmidt says, is “it was a very strange year... The more you dig into it, the less clear it seems.”

One part of that is the timing for when 2023's big burst of heat began, according to Schmidt and Samantha Burgess, deputy director of Europe's Copernicus Climate Service, which earlier this week put warming at 1.48C above pre-industrial times.

Temperatures are typically highest above normal in late winter and spring, they say. But 2023's highest heat kicked in around June and lingered at record levels for months.

Deep ocean heat, a big player in global temperatures, behaved in a similar way, Burgess says.

Is global warming accelerating faster than predicted?

Former NASA climate scientist James Hansen, often considered the godfather of global warming science, theorised last year that warming was accelerating. While many of the scientists contacted by AP said they suspect it is happening, others were adamant that evidence so far supports only a steady and long-predicted increase.

“There is some evidence that the rate of warming over the past decade or so is slightly faster than the decade or so previous - which meets the mathematical definition of acceleration,” says UCLA climate scientist Daniel Swain. “However, this too is largely in line with predictions” that warming would accelerate at a certain point, especially when particle pollution in the air decreases.

The US National Oceanic and Atmospheric Administration (NOAA) calculated that Earth in 2023 had an average temperature of 15.08C. That’s 0.15C warmer than the previous record set in 2016 and 1.35C warmer than pre-industrial temperatures.

“It’s almost as if we popped ourselves off the staircase [of normal global warming temperature increases] onto a slightly warmer regime,” says Russ Vose, global monitoring chief for NOAA’s National Centers for Environmental Information. He says he sees acceleration of warming.

NASA and the United Kingdom Meteorological Office had the warming since the mid-19th century a bit higher at 1.39C and 1.46C respectively. Records go back to 1850.

The World Meteorological Organization, combining the measurements announced Friday with Japanese and European calculations released earlier this month, pegged 2023 at 1.45 degrees Celsius warmer than pre-industrial temperatures.

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Is a warming limit of 1.5C still achievable?

Many of the climate scientists saw little hope of stopping warming at the 1.5-degree goal called for in the 2015 Paris agreement that sought to avert the worst consequences of climate change.

“I do not consider it realistic that we can limit warming [averaged over several years] to 1.5C,” says Woodwell Climate Research Center scientist Jennifer Francis. “It is technically possible but politically impossible.”

“The slow pace of climate action and the continued disinformation that catalyses it has never been about lack of science or even lack of solutions: it has always been, and remains, about lack of political will,” says Katharine Hayhoe, chief scientist at The Nature Conservancy.

Both NASA and NOAA said the last 10 years, from 2014 to 2023, have been the 10 hottest years they’ve measured. It’s the third time in the last eight years that a global heat record was set. Randall Cerveny, an Arizona State University scientist who helps coordinate record-keeping for the WMO, says the big worry isn’t that a record was broken last year, but that they keep getting broken so frequently.

“It’s the rapidity of the continual change that is, to me, most alarming,” Cerveny says.

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Cornell University climate scientist Natalie Mahowald says, “This is just a taste of what we can expect in the future, especially if we continue to fail to cut carbon dioxide fast enough.”

That's why so many scientists contacted by The Associated Press are anxious.

“I've been worried since the early 1990s,” says Brown University climate scientist Kim Cobb. “I am more worried than ever. My worry increases with every year that global emissions move in the wrong direction.”