Summer 2023 was the hottest in 2,000 years, study says

An extreme summer marked by deadly heat waves, explosive wildfires and record-breaking ocean temperatures will rank among the hottest in the past 2,000 years, according to new research.

In the summer of 2023, temperatures in the Northern Hemisphere soared 3.72 degrees above the average from 1850 to 1900, when modern instrumental record-keeping began, according to a study published Tuesday in the journal Nature. The study focused on surface air temperatures in the extratropics, which lies between 30 and 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 for years 1 to 1890, which the researchers calculated by combining observed records with tree-ring records from nine global regions.

Jan Esper, lead author of the study and professor of climate geography at Johannes Gutenberg University in Germany, said he didn't expect last year's summer to be so anomalous, but ultimately wasn't surprised by the findings. The high temperatures added to a general warming trend driven by greenhouse gas emissions and were further amplified by the onset of El Niño in the tropical Pacific.

“It's not a surprise, this really extraordinary 2023, but it was also, step by step, a continuation of a trend that will continue,” Esper told reporters on Monday. “Personally, it doesn't surprise me, but it does worry me.”

He said it was important to put the extreme temperatures of 2023 in a long-term context. The difference between the region's previous warmest summer, in 246, and the summer of 2023 is 2.14 degrees, according to the study.

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

“Although 2023 is consistent with a greenhouse gas-induced warming trend that is amplified by the developing El Niño event, this extreme emphasizes the urgency of implementing international agreements for the reduction of carbon emissions,” it says. the study.

Sweltering summer temperatures contributed to dozens of heat illnesses and deaths, including at least 645 heat-related deaths in Maricopa County, Arizona, where Phoenix recorded temperatures of 110 degrees or higher for a record 31 consecutive days.

Wildfires exacerbated by high temperatures swept through Canada, sending dangerous smoke up the East Coast of the United States and across the Atlantic. Meanwhile, the ocean temperature off the coast of 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, declared 2023 the hottest year on record globally.

In particular, Copernicus found that the summer months of June, July and August last year were 1.18 degrees warmer than average; still hot, but not as warm as the study's findings for the extratropical region of the northern hemisphere.

That region was especially hot in part because it is home to a lot of land, which is warming faster than the 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 compared to measurable data dating back to the mid-19th century. But by going back 2,000 years, the researchers also helped illuminate “the whole range of natural variability that could have occurred in the past,” she said.

He noted that tree rings can serve as a useful indicator of past climatic conditions, as trees tend to grow larger in a given year if they receive the right amount of heat, water and sunlight.

But while last year's heat was undeniable, the study also highlights 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 during the pre-industrial period, established by the Intergovernmental Panel on Climate Change in 2015.

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

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

McKinnon said there will always be some degree of uncertainty when comparing current temperatures to past temperatures, but the 1.5 degree 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 it well enough to say that 1.5 C is he temperature for certain inflection points,” he said. “This is just a policy goal that provides a temperature change that would perhaps be consistent with preventing some harm.”

In fact, the release of the study comes days after a survey of 380 leading IPCC scientists 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 scientists surveyed believe the 1.5 degree limit will be reached. Nearly 80% said they expect at least 2.5 degrees Celsius of warming.

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

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

In fact, as scientists continue to weigh whether or how quickly humanity can alter the planet's increasing warming trajectory, Esper said he hopes the latest study will serve as motivation to change outdated modes of energy consumption that contribute to greenhouse gases that warm the planet. .

“I'm concerned about global warming; I think it's one of the biggest threats out there,” he said.

He added that he is particularly concerned about his children and the younger generations, who will be most affected by worsening heat and other adverse climate outcomes. According to the study, there is a high probability that the summer of 2024 will be even hotter.

“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 very obvious: we must do everything we can, as soon as possible.”