Ancient trees open up a worrying new look at our warming world

CNN
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Last summer, I excelled Deadly extreme heat And Devastating forest firesIt was the warmest weather in at least 2,000 years, according to new research, which analyzed weather and tree-ring data to reconstruct a detailed picture of the past.

The findings provide a stark look at the “unprecedented” global warming the world is experiencing today thanks to humans burning massive amounts of planet-warming fossil fuels, according to the study’s authors. Stady Published Tuesday in the journal Nature. This is a worrying sign as some scientists warn that 2024 is on its way be hotter Still.

Global warming is currently tracked by comparing temperatures to the “pre-industrial era,” before humans began burning large amounts of fossil fuels, widely known as the period 1850 to 1900. Under the Paris Agreement in 2015, Countries agreed to limit global warming. to two degrees above pre-industrial levels.

Last summer, the world temporarily crossed this threshold, according to the report. Using data from temperature gauges during this period, scientists found that the Northern Hemisphere summer in 2023 was 2.07 degrees Celsius warmer than the pre-industrial period.

But observational data from this period are sparse, uncertain, and tend to be skewed. So, to get a fuller picture of how the climate varied naturally before the start of the pre-industrial era, the study authors looked much further into the past.

To do this, they used detailed sets of tree-ring records from thousands of trees across nine regions of the Northern Hemisphere, including North America and Scandinavia, but excluding tropical regions that lack good tree data.

Trees act as time capsules. Their ring patterns – influenced by sunlight, rain and temperature – provide a climatic history for each year of their lives, going back centuries or even millennia.

This complex tree-ring data allowed scientists to reconstruct the annual temperatures of Northern Hemisphere summers between the years 1 and 1849 and compare them to the temperatures of the previous summer.

They found that the summer of 2023 was warmer than any other summer during this period.

The weather was at least 0.5°C warmer than the warmest summer during this period, in 246 – when the Roman Empire still ruled Europe and the Maya civilization dominated Central America.

At the other end of the scale, last summer was about 4 degrees Celsius warmer than the coldest summer identified by the study, the year 536, when a volcanic eruption pumped massive amounts of cooling gases into the planet.

Using this data set going back 2,000 years, they calculated that the summer of 2023 was 2.2 degrees Celsius hotter than the long-term pre-industrial average, before powerful networks of instruments could measure the weather.

This study comes on the heels of a report published in November, which found that humanity has lived through a period of time The hottest 12-month period in at least 125,000 years. The study, and others like it, rely on data extracted from other proxies, such as ice cores and coral reefs, which don’t give the same detailed annual evidence as tree rings.

This makes it difficult to compare individual days or even years with those in the past, said Jan Esper, lead author of the study and professor of climate geography at Johannes Gutenberg University in Germany.

He added that it is possible – even likely – that last year was the hottest in at least 125,000 years, but “we don’t have the data” to say that for sure.

A deep dive into annual temperatures in Northern Hemisphere summers is a “worthwhile endeavor,” said Kim Cobb, a climate scientist at Brown University who was not involved in the study.

What’s impressive is that “we have enough temperature reconstructions from enough places around the world to document the exceptional nature of a single year of widespread extreme temperatures,” she told CNN.

She added that this “treasure trove of data” could be used to “sharpen our expectations about future climate extremes.”

While the study can put the unusual heat in the Northern Hemisphere into historical context, it cannot be applied on a global scale, Esper said. There simply isn’t enough data on tree rings from the Southern Hemisphere and the tropics, he said.

Esper said that the results of the study are deeply disturbing. “There are potentially irreversible processes in the system, and I am not afraid of that for myself. “I am old,” he added. “I am worried for the children.”

CNN’s Laura Baddison contributed to this report.