Los Angeles Times

Summer of 2023 was hottest in 2,000 years

Warming was driven by greenhouse gas emissions, amplified by El Niño, study says.

- By Hayley Smith

An extreme summer marked by deadly heat waves, explosive wildfires and record warm ocean temperatur­es will go down as among the hottest in the last 2,000 years, new research has found.

The summer of 2023 saw the temperatur­e in the Northern Hemisphere soar 3.72 degrees above the average from 1850 to 1900, when modern instrument­al recordkeep­ing began, according to a study published Tuesday in the journal Nature. The study focused on surface air temperatur­es across the extra-tropical region, which sits at 30 to 90 degrees north latitude and includes most of Europe and North America.

June, July and August last year were also 3.96 degrees warmer than the average from the years 1 through 1890, which the researcher­s calculated by combining observed records with tree ring records from nine global regions.

Jan Esper, the study’s lead author and a professor of climate geography at Johannes Gutenberg University in Germany, said that he was not expecting summer last year to be quite so anomalous, but that he was ultimately not surprised by the findings. The high temperatur­es built on an overall warming trend driven by greenhouse gas emissions and were further amplified by the onset of El Niño in the tropical Pacific.

“It’s no surprise — this really, really outstandin­g 2023 — but it was also, stepwise, a continuati­on of a trend that will continue,” Esper told reporters Monday. “Personally I’m not surprised, but I am worried.”

He said it was important to place 2023’s temperatur­e extreme in a long-term context. The difference between the region’s previous warmest summer, in the year 246, and the summer of 2023 is 2.14 degrees, the study found.

The heat is even more extreme when compared with the region’s coldest summers — the majority of which were influenced by volcanic eruptions that spewed heat-blocking sulfur into the stratosphe­re. According to the study, 2023’s summer was 7.07 degrees warmer than the coldest reconstruc­ted summer from this period, in the year 536.

“Although 2023 is consistent with a greenhouse gases-induced warming trend that is amplified by an unfolding El Niño event, this extreme emphasizes the urgency to implement internatio­nal agreements for carbon emission reduction,” the study says.

The sweltering summer temperatur­es contribute­d to scores of heat illnesses and deaths, including at least 645 heat-associated deaths in Maricopa County, Ariz., where Phoenix saw temperatur­es of 110 degrees or hotter for a record 31 consecutiv­e days.

Wildfires exacerbate­d by high temperatur­es raged across Canada and sent hazardous smoke down the East Coast of the United States and across the Atlantic. Meanwhile, ocean temperatur­es off Florida soared above 101 degrees, the temperatur­e of a hot tub.

Multiple climate agencies, including the National Oceanic and Atmospheri­c Administra­tion and the European Union’s Copernicus Climate Change Service, have declared 2023 the hottest year on record globally.

Notably, Copernicus found that the summer months of June, July and August last year measured 1.18 degrees warmer than average — still hot, but not nearly as warm as the study’s findings for the Northern Hemisphere’s extra-tropical region.

That region was especially hot in part because it is home to so much land, which warms faster than oceans, said Karen McKinnon, an assistant professor of statistics and the environmen­t at UCLA who did not work on the study. (June, July and August are also winter months in the Southern Hemisphere.)

McKinnon said the study’s findings are not unexpected, as there was already good evidence that the summer of 2023 was record-breaking when compared with measurable data going back to the mid-1800s. But by going back 2,000 years, the researcher­s also helped illuminate “the full range of natural variabilit­y that could have occurred in the past,” she said.

She noted that tree rings can serve as a helpful proxy for climate conditions in the past, as trees tend to grow more in a given year if they receive the right amount of warmth, water and sunshine. But although last year’s heat was undeniable, the study also underscore­s that the summer temperatur­e in this region was notably higher than the global target of 2.7 degrees — or 1.5 degrees Celsius — of warming over the preindustr­ial period, which was establishe­d by the Intergover­nmental Panel on Climate Change in 2015.

It also notes that some recent research has found the data used to calculate that baseline may be off by several tenths of a degree, meaning it could need to be recalibrat­ed, with the target landing closer to an even more challengin­g 1.6 or 1.7 degrees.

“I don’t think we should use the proxy instead of the instrument­al data, but there’s a good indication that there’s a warm bias,” Esper said. “Further research is needed.”

McKinnon said there is always going to be some degree of uncertaint­y when comparing present-day temperatur­es to past temperatur­es, but that the 1.5degree limit is as symbolic as it is literal. Many effects of climate change, including worsening heat waves, have already begun.

“There are definitely tipping points in the climate system, but we don’t understand the climate system well enough to say 1.5 C is the temperatur­e for certain tipping points,” she said. “This is just a policy goal that gives you a temperatur­e change that maybe would be consistent with averting some damages.”

In fact, the study’s publicatio­n comes days after a survey of 380 leading scientists from the IPCC revealed deep concerns about the world’s ability to limit global warming to 1.5 degrees. That report, published last week in the Guardian, found that only 6% of surveyed scientists think the 1.5-degree limit will be met. Nearly 80% said they foresee at least 2.5 degrees Celsius of warming.

The report caused a stir among the scientific community, with some saying it focused too heavily on pessimism and despair. But Daniel Swain, a climate scientist with UCLA who participat­ed in the survey, said its findings are worthy of considerat­ion.

“There are many kinds of scientists, myself included, who are very worried and concerned and increasing­ly alarmed by what is going on and what the data is showing,” Swain said during a briefing Friday. “But if anything, I think that really results in a stronger sense of resolve and urgency to do even more, and to do better.”

Indeed, while scientists continue to weigh in on whether — or how quickly — humanity can alter the planet’s worsening warming trajectory, Esper said he hopes the latest study will serve as motivation for changing outdated modes of energy consumptio­n that contribute to planet-warming greenhouse gases.

“I am concerned about global warming — I think it’s one of the biggest threats out there,” he said.

He added that he is particular­ly worried for his children and for younger generation­s who will bear the brunt of adverse climate outcomes. There is a strong likelihood that the summer of 2024 will be even hotter, the study says.

“The longer we wait, the more extensive it will be, and the more difficult it will be to mitigate or even stop that process and reverse it,” Esper said. “It’s just so obvious: We should do as much as possible, as soon as possible.”

 ?? Edmar Barros Associated Press ?? RIVERSIDE residents carry aid amid drought fueled by anthropoge­nic climate change in Brazil’s Amazonas state last year. In the Northern Hemisphere, climate change contribute­d to 2023’s record-setting summer.
Edmar Barros Associated Press RIVERSIDE residents carry aid amid drought fueled by anthropoge­nic climate change in Brazil’s Amazonas state last year. In the Northern Hemisphere, climate change contribute­d to 2023’s record-setting summer.

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