2023 Temperatures Were Warmest We've Seen For At Least 2,000 Years

An anonymous reader quotes a report from Ars Technica: Starting in June of last year, global temperatures went from very hot to extreme. Every single month since June, the globe has experienced the hottest temperatures for that month on record -- that's 11 months in a row now, enough to ensure that 2023 was the hottest year on record, and 2024 will likely be similarly extreme. There's been nothing like this in the temperature record, and it acts as an unmistakable indication of human-driven warming. But how unusual is that warming compared to what nature has thrown at us in the past? While it's not possible to provide a comprehensive answer to that question, three European researchers (Jan Esper, Max Torbenson, and Ulf Buntgen) have provided a partial answer: the Northern Hemisphere hasn't seen anything like this in over 2,000 years. [...] The first thing the three researchers did was try to align the temperature record with the proxy record. If you simply compare temperatures within the instrument record, 2023 summer temperatures were just slightly more than 2C higher than the 1850-1900 temperature records. But, as mentioned, the record for those years is a bit sparse. A comparison with proxy records of the 1850-1900 period showed that the early instrument record ran a bit warm compared to a wider sampling of the Northern Hemisphere. Adjusting for this bias revealed that the summer of 2023 was about 2.3 C above pre-industrial temperatures from this period. But the proxy data from the longest tree ring records can take temperatures back over 2,000 years to year 1 CE. Compared to that longer record, summer of 2023 was 2.2 C warmer (which suggests that the early instrument record runs a bit warm). So, was the summer of 2023 extreme compared to that record? The answer is very clearly yes. Even the warmest summer in the proxy record, CE 246, was only 0.97 C above the 2,000-year average, meaning it was about 1.2 C cooler than 2023. The coldest summer in the proxies was 536 CE, which came in the wake of a major volcanic eruption. That was roughly 4 C cooler than 2023. While the proxy records have uncertainties, those uncertainties are nowhere near large enough to encompass 2023. Even if you take the maximum temperature with the 95 percent confidence range of the proxies, the summer of 2023 was more than half a degree warmer. Obviously, this analysis is limited to comparing a portion of one year to centuries of proxies, as well as limited to one area of the globe. It doesn't tell us how much of an outlier the rest of 2023 was or whether its extreme nature was global. The findings have been published in the journal Nature.

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