Oct 12, 2023 - Energy & Environment

Scientists "uneasy" about Earth's sped-up warming

A global map showing sea surface temperature deviation from the 1971-2000 mean. Boxes indicate the El Niño region and "Main Development Region" for Atlantic hurricanes. Data: NOAA; Graphic: Axios Visuals

The globe's pronounced and unexpected temperature spike during the past few months is provoking unease among some of the most level-headed climate scientists.

The big picture: September was the most unusually warm month in recorded history. This followed record heat in June and July — which was also the planet's hottest month — as well as August.

  • Climate scientists point to several factors propelling the climate into uncharted territory. These include a strengthening El Niño in the tropical Pacific Ocean to an undersea volcanic eruption last year, which injected water vapor into the upper atmosphere.
  • Other developments, such as changes in fuel mixtures for large marine vessels and weather patterns in the North Atlantic, are coming under scrutiny too.

Of note: Yet the largest factor at work is long-term, human-caused climate change from burning fossil fuels like coal and gas.

Yes, but: The climate scientists Axios spoke with for this story noted there may be some aspects of the recent record-shattering global heat that are not fully understood.

  • This isn't reason for panic, however; but it does showcase that climate change involves surprises.
  • And as the climate continues to warm, there may be even more consequential and unforeseen shocks down the road.
  • "Future researchers will be writing dissertations trying to unpack the mix of factors that led us to blow away all prior records this year," Zeke Hausfather, climate lead at the payments company Stripe, told Axios.

Between the lines: The Pacific Ocean has seen a rapid swing from a cool, three-year-long La Niña phase into an El Niño, which features unusually mild ocean temperatures in the central and eastern tropical Pacific.

  • That may be pushing global average surface temperatures higher at faster-than-usual rates.
  • "Climate change comes on top of natural fluctuations in the climate system, and in a hotter-than-average world there will be hotter and cooler years," Kate Marvel, a senior climate scientist at Project Drawdown, told Axios.
  • "The usual suspects — climate change plus El Niño — go a long way toward explaining the excess heat of this summer," Marvel said. She cautioned that other sources of internal variability may be at play too and historically have led to unexpected outcomes.
  • "There is always the possibility that something is going on that we've missed, but the Earth system is a strange beast even when it's not being disturbed," Marvel said.

Zoom out: At the start of the calendar year, few climate experts expected it would be the planet's warmest on record. Yet that is now a virtual lock in nearly every data set, from NASA to the Copernicus Climate Change Service.

  • Much of the planet's high fever is traceable to record warm oceans worldwide, a characteristic of 2023's climate imperiling sensitive marine ecosystems.
  • Berkeley Earth, an independent temperature tracking group, pegs the odds that 2023 will have a global average surface temperature that is more than 1.5°C (2.7°F) above pre-industrial levels at 90%, up from just 55% one month ago, and 1% before the year began.
  • This is a symbolic milestone, since it is the more ambitious target in the Paris Climate Agreement. However, the Paris text refers to an average over multiple decades, not a single year.
  • "The fact that this forecast has shifted so greatly serves to underscore the [extraordinary] progression of the last few months, whose warmth has far exceeded expectations," Berkeley Earth's Robert Rohde wrote in an analysis published Wednesday.

What they're saying: Andrew Dessler, a climate scientist at Texas A&M University, said the "sudden jump" in temperatures during just a few months' time has been the biggest surprise.

  • Because all of the human-caused responses act on longer and slower time scales, this would suggest some combination of internal, largely natural climate variability, together with climate change.
  • "It may be some compound mode or something weirder," he said, noting that while the temperature uptick is not a completely unforeseen outcome in climate model simulations, they depict it as being highly unlikely.
  • "I think this makes everybody in the climate science community uneasy."
  • Gavin Schmidt is the director of NASA's Goddard Institute for Space Studies, which is slated to release its September temperature data on Friday. He expects the temperature departures from average to shrink each month as we head into winter in the Northern Hemisphere.
  • Yet with the strong to very strong El Niño forecast to last into 2024, global average temperatures are likely to stay unusually high. Typically, global temperatures peak a few months after El Niño does.

The bottom line: "2023 will be the warmest year (something I gave a 10% probability to at the end of 2022), but I think 2024 will be warmer still," Schmidt said.

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