The summer of 2023 was the warmest in the northern hemisphere in the last 2,000 years. This is indicated by a team of climatologists who have carefully tracked these temperatures and who publish their research in the journal Nature. It was known that the year 2023 has been the warmest year on the entire planet since the pre-industrial era. But that information is obtained with instrumental data dating back to 1850. The novelty is that scientists have reconstructed and completed the summer temperatures year by year since the year 1 AD. C. to the present day helped with a record of thousands of tree rings.
“No year even came close to the intense heat of last summer,” said the study’s lead author, Jan Esper, a geographer and climatologist at the Gutenberg Research College in Germany.
To carry out their work, the team of climatologists has used a data set that combines instrumental observations, available since the 19th century, and reconstructions based on databases focused on the growth of the rings of the trees, which allow us to go back years.
This has analyzed the evolution of surface air temperatures from June to August in regions outside the tropics of the northern hemisphere (an area that covers areas that include Europe) over the last 2,000 years.
The conclusion is that land temperatures in these regions have been 2.07°C higher in 2023 (June, July and August) than the average between 1850 and 1900.
Additionally, to investigate trends over the past 2,000 years, the authors reconstructed temperatures from the longest available chronologies of temperature-sensitive trees.
And, with this broader focus, they discovered that the summer of 2023 exceeded the average of the longest-term period from year 1 to 1890 by 2.20ºC.
For this reason, they describe as “alarming” the fact that in the summer of 2023 the temperatures were 2.07ºC warmer than those of the first instrumental records. And they qualify it this way, remembering that the Paris agreement against warming (2015) sets the goal of ensuring that global warming does not exceed 1.5ºC.
In addition, they offer an explanation for why temperatures have risen 2.07ºC according to recent instrumental records, but exceeded 2.20ºC if we go back to the period 1-1900 prior to instrumental records.
And the difference has to do with the extensive cold periods in these 2,000 years: that of the Little Ice Age of Late Antiquity (a cooling episode of the northern hemisphere between the 6th and 7th centuries) and the Little Ice Age, of the early 19th century.
This kind of climate history since Roman times offers interesting conclusions. For example, the summer that turned out to be the coldest in this reconstruction is that of the year 536 AD. C. (-1.86ºC, compared to the period 1850 and 1900).
Specifically, the summer temperature of 2023 has been 3.93°C warmer compared to that of the year 536 AD, when temperatures were influenced by a volcanic eruption.
Before humans started pumping heat-trapping gases into the atmosphere by burning coal, oil and natural gas, the hottest year was 246 AD, Jan Esper said.
In this way, the record record of 2023 was 1.2ºC higher than that of that year in Roman times.
In fact, 25 of the last 28 years have been hotter than that summer of 246-
Even considering the relatively high degree of uncertainty offered by these reconstructions (between -0.03 and 1.50ºC for the year 246 AD), “the summer of 2023 exceeded the range of natural climate variability with a minimum of more than 0. 5ºC”, says the report.
The team used thousands of trees at 15 different sites in the northern hemisphere, north of the tropics, where there was enough data.
The study also illustrates how “the most notable warming episodes are associated with strong El Niño events.”
The extremely hot summer of 2023 exceeded by 0.23ºC the records of the summer of 2016 previously affected by El Niño. Furthermore, its current phase has not yet concluded and “the current El Niño is forecast to last until early summer 2024,” the authors recall.
Usually, there is a delay between the extreme conditions of this phenomenon and long-term temperature deviations, which suggests that “2024 will see record temperatures again.”
Three factors derived from this phenomenon are notable.
A persistent El Niño episode culminated in 1992, but did not lead to warming, since this event coincided with the eruption of the Pinatubo volcano (Philippines) in June 1991, which released large quantities of sulfur into the atmosphere, obscuring the sky and caused a cooling during the following years
Secondly, the temperatures recorded in 1998, greatly altered by another runaway El Niño, were not surpassed in 2003 and this gave way to a period called “temperature pause”: a decade during which global temperatures did not rise above from the level of the end of the century.
However, that pause ended in 2010, when an El Niño episode stronger than in 2003 arrived and resulted in temperatures exceeding those of the summer of 1998 by 0.36ºC.
Third, the lack of warming until the mid-1980s was probably affected by a global dimming phenomenon, a phenomenon that alludes to changes in atmospheric transmission and cloudiness due to increased aerosol emissions during the warming stage. postwar economic expansion. This cooling factor “faded in the 1980s, when effective sulfur decontamination measures were established in Europe and North America,” the study says.
All of these increases are judged to be consistent and “in line with the underlying upward trend in greenhouse gas concentrations.”
