Summer 2023: Northern Hemisphere’s Hottest In 2 Millennia

Tree rings suggest that the summer of 2023 in the Northern Hemisphere may have been the hottest in 2,000 years, with temperatures rising by 3.9 degrees Celsius over the coldest summer during the same period.

4 Degrees Celsius Higher

Climate change has previously proven that last year was the warmest on record globally, at least since 1850. However, tree rings, which go back much further than even Victorian scientific records in terms of temperature data, now demonstrate just how exceptional this year's searing temperatures were.

According to researchers, the most recent June, July, and August temperatures were almost 4 degrees Celsius higher than the coldest summer that occurred two millennia ago.

Because they are susceptible to variations in temperature and precipitation, trees offer a window into historical climates. Their growth rings, which spread out more in warm, rainy years than they do in cold, dry ones, are where this knowledge gets crystallized.

After analyzing tree-ring data that went all the way back to the height of the Roman Empire, the scientists came to the conclusion that 2023 stood out even after taking into consideration historical fluctuations in climate.

"When you look at the long sweep of history, you can see just how dramatic recent global warming is," co-author Ulf Büntgen, a professor of environmental systems analysis at the University of Cambridge in the U.K., said.

Furthermore, the results showed that the Paris Agreement's 1.5-degree Celsius target-which was intended to slow global warming and avert the worst effects of climate change-has already been exceeded by the Northern Hemisphere.

El Niño

The researchers pointed out that larger El Niño episodes, such as the one that occurred in 2023, have been caused by growing emissions and global warming, but they nevertheless connected El Niño events to many of the warmer summers in the tree ring data.

The finding did not come as a complete surprise. By January, researchers with the Copernicus Climate Change Service of the European Union declared that 2023 was "very likely" to be the warmest year in around a million years.

Jan Esper, a climate scientist at Johannes Gutenberg University in Germany and co-author of the study, stated that it is improbable that such a lengthy record can be proven.

In an article published last year, he and two other European scientists contended that the techniques used by science today-such as extracting temperature data from peat bogs or marine sediments-could not be used to generate year-by-year comparisons over a period of time this extensive.

According to the findings of a second study, which opened a new tab published on Tuesday in the journal PLOS Medicine, heatwaves are already having a negative impact on people's health, with over 150,000 deaths in 43 countries due to heatwaves each year between 1990 and 2019.

That would be equivalent to 1% of all deaths worldwide, or nearly the same number as the COVID-19 pandemic. Over 50% of the additional deaths attributed to heatwaves happened in densely populated Asia.