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Antique trees reveal a concerning fresh perspective on a warming planet.

Summer of last year, characterized by deadly heat extremes and destructive wildfires, likely the warmest in at least 2,000 years, indicates recent study.

A traffic warden in Las Vegas, Nevada on July 12, 2023, where temperatures reached 106 degrees amid...
A traffic warden in Las Vegas, Nevada on July 12, 2023, where temperatures reached 106 degrees amid a heatwave

Antique trees reveal a concerning fresh perspective on a warming planet.

The recent report published in the journal Nature offers a clear portrayal of the current unparalleled warming caused by humans burning a massive amount of fossil fuels that heat up our planet. The alarming news is that 2024 could even surpass this temperature despite warnings from some scientists.

Global warming is typically monitored by comparing current temperatures to the pre-industrial era, which is the period before humans started burning significant amounts of these fuels, typically between 1850 and 1900. Under the Paris Agreement in 2015, countries pledged to limit global warming to 2 degrees above the pre-industrial levels.

During the previous summer, the world briefly surpassed this mark, according to the study. The scientists took temperature data gathered during this period and discovered that the Northern Hemisphere's summer in 2023 was 2.07 degrees Celsius warmer than those pre-industrial levels.

However, this observational data has its limitations. It is sparse, uncertain, and tends to overestimate warmth. To get a more accurate picture of climate variation before the beginning of the pre-industrial era, the authors of the study looked much further back in time.

Using detailed tree ring records from thousands of trees in nine regions of the Northern Hemisphere, including North America and Scandinavia, but excluding the Tropics where there is insufficient high-quality tree data, they painstakingly researched and analyzed the patterns in the rings. These patterns, impacted by sunlight, rainfall, and temperature, provide a climate history for each year of each tree's life, spanning countless centuries or even millennia.

By using this complex tree ring data, the scientists were able to reconstruct annual temperatures for Northern Hemisphere summers from the year 1 to 1849, then compare them with the temperatures from the summer of 2023. The result? The 2023 summer was warmer than any other summer in all those years.

It was at least 0.5 degrees Celsius hotter than the warmest summer during that period, which was in 246 AD when the Roman Empire was still in power, and the Mayan Civilization spread across Central America. On the other end of the spectrum, the 2023 summer was almost 4 degrees Celsius warmer than the coldest summer the study identified, in 536 AD, when a volcanic eruption released copious amounts of planet-cooling gases. If we look at the entire 2,000-year timeframe, the 2023 summer was 2.2 degrees Celsius hotter than the average pre-industrial temperature.

A tourist cooling down in a fountain amid a heatwave in Barcelona, Spain, on July 19, 2023.

An earlier report in November found that the previous 12-month period was the hottest in at least 125,000 years, but it relied on data from proxies that are not as comprehensive as tree rings, such as ice cores and coral reefs. These sources can't provide yearly evidence as precise as tree rings.

Despite the possibility that 2022 was indeed the hottest in 125,000 years, definitive proof is difficult because we lack reliable data spanning those years. Lead author Jan Esper, a professor of climate geography at Johannes Gutenberg University in Germany, suggested that we might be on track to break the record, but we're missing the data needed to make that conclusion with certainty.

This in-depth analysis of the year-by-year temperature changes in the Northern Hemisphere is a worthwhile endeavor, according to Kim Cobb, a climate scientist at Brown University who didn't take part in this study. What's remarkable, she commented, is that we have collected enough tree ring data from different parts of the world to accurately document the exceptional heat of a single year.

This treasure trove of data can help improve projections of future climate extremes and prepare for them more effectively. However, Esper stressed that the findings could not be applied globally because there isn't enough tree ring information from the Southern Hemisphere or the Tropics.

As worrying as these results are, Esper warned, "There are potential irreversible processes in the system, and I'm afraid, not for me. I'm old. I'm more concerned for the kids."

(CNN's Laura Paddison contributed to this report.)

People use umbrellas and parasols to seek relief from the heat in Tokyo on July 30, 2023.

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