The summer of 2023 was the hottest in two thousand years

The summer of 2023 was the hottest in two thousand years

The summer of 2023 was the warmest in the past 2,000 years. Scientists conclude this based on historical growth ring data of trees. The average summer temperature can be deduced from the width of the rings that trees form annually. The study is not a global analysis, but is limited to the land area of ​​the Northern Hemisphere between the 30th and 90th parallel. The results have been published in an accelerated manner Nature.

The researchers conducted their study as a kind of test for the measurement data used by the IPCC, the United Nations climate agency, for the period 1850-1900. The IPCC calls this the reference period for the pre-industrial era, and based on that period calculates how much the earth has now warmed. But, the researchers write in their article, the data for that period comes from “only 58 measuring stations” worldwide that existed at the time. And 45 of them were in Europe. All 58 measuring stations were located between 30 degrees (near Cairo and New Orleans) and 90 degrees (the North Pole) north latitude.

Tree ring databases

In their study, the researchers compare the data from these measuring stations with that from nine annual ring databases of trees, which represent the Northern Hemisphere. An additional advantage is that the tree ring dates go back much further in time. In this case they start in the year 1 AD.

The tree ring dates indicate 246 AD. emerges as the year with the warmest summer (measured over the months of June, July, August) if we look back to 1849. In that summer the average temperature was 0.88 degrees Celsius above the average for the period 1850-1900. For the summer of 2023, that average is 2.07°C above the 1850-1900 average. “That is really a huge difference,” says climate scientist Hylke de Vries of the KNMI, who was not involved in the study.

The first author of the article, Jan Esper, professor of climate geography at the University of Mainz, said during a press conference that he was not really surprised by the result. “But concerned,” he said, because global warming jumped again last year. In addition to the structural warming of the earth due to the increasing concentration of greenhouse gases in the atmosphere, this is due to the occurrence of an El Niño in the Pacific Ocean, which introduces extra heat into the atmosphere. This climate phenomenon, which occurs once every two to seven years, is still ongoing. But the American research institute NOAA reported last week a strong weakening of El Niño in the past month, and expects its end soon.

His colleague Max Torbenson was asked during the press conference whether there had been more summers in recent years that were warmer than in the year 246. “For the past 28 years, this applies to 25 summers,” he said, after briefly have looked up.

Another outcome of the research is that the average temperature over the period 1850-1900 based on the annual ring data of trees is 0.24°C lower than based on the data from the 58 measuring stations. “Our current climate will not change as a result,” says De Vries. “But if the data is correct, it means that the Earth has warmed even more since that period than we already thought.” In the Synthesis report, published in March 2023, the IPCC writes that the Earth’s surface (land and oceans) has warmed by 1.1°C since the period 1850-1900. Based on the tree ring data, this would be more. And that would mean, says De Vries, that we must do even more to comply with the agreements made in the Paris Climate Agreement (2015), which stipulates that we should limit warming to 2°C, and preferably up to 1.5°C. The researchers also emphasize the urgency of reducing greenhouse gas emissions.

Dutch heat record

In the report published this Tuesday Climate risks in the Netherlands the Netherlands Environmental Assessment Agency underlines how quickly the climate is changing. The Dutch heat record of more than 40°C, from 2019, came decades earlier than expected. The Netherlands will have to make drastic adjustments, according to the PBL. This adjustment, the agency writes, “should now guide spatial policy, housing policy and nature and agricultural policy, among other things.”




SCIENCE