Have we already crossed the 1.5°C global warming limit? New study suspects this: “Even 2.0°C is possible by 2030” | Science and the planet

Have we perhaps already crossed the 1.5°C warming limit? a New study Which appeared today in the scientific journal Nature Climate Change suggests yes. Scientists came to this conclusion after analyzing 300 years of ocean temperature measurements preserved in sponge skeletons from the Caribbean. It also means that average global temperature rise is likely to exceed 2 degrees Celsius by the end of this decade.

How did scientists reach this conclusion?

Unfortunately, historical observations of ocean temperatures are limited. Sea temperatures did not begin to be recorded by ship measurements until the 1850s.2 However, human activity began in the early 1800s, so to understand our overall impact on temperatures, you need data from before then.

The alternative is so-called “proxy data,” which are so-called indirect measurements that give us a look into the past. Just think of ice measurements, for example. A valuable proxy for studying ocean temperatures is the “hard sponge.” This is a long-lived marine animal known to record chemical changes in its skeleton. This is how strontium (Sr) and calcium (Ca) are stored. The ratio between them can be used as a historical thermometer. Lower values ​​occur during warmer periods and higher during colder periods.

The average warming between 2018 and 2022 will already be +1.7°C.

In this study, scientists used hard sponges from the eastern Caribbean Sea, a region with more stable temperatures. Thus, they experienced a 300-year temperature series. They can then compare this with available seawater temperature data to see if their series is reliable. This was the case.

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What are the new findings of the study?

The new temperature series offers a revised view of global warming. Based on hardened sponge data, scientists first determined stable pre-industrial temperatures for the periods 1700-1790 and 1840-1860. Then they saw that human global warming had been occurring since the mid-1860s and had already begun by the mid-1870s. This is about 80 years earlier than sea surface temperature measurements indicate, but is more consistent with previous climate reconstructions.

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Temperature rise on land and in the ocean.
Temperature rise on land and in the ocean. © McCulloch et al., 2024 in Nature Climate Change

When scientists looked at the most recent temperatures recorded by hard sponges, they saw the following. In the period 1961-1990, the temperature actually rose by 0.9°C compared to the newly calculated pre-industrial period. According to old estimates, this was only 0.4°C. According to researchers, this means we may have already reached a temperature rise of +1.5 degrees Celsius. The average increase between 2018 and 2022 will be +1.7°C. This review also suggests that the Earth may exceed the critical limit of +2°C as early as 2030, 20 years earlier than expected at the current CO2 level.2emissions.

The authors stress that further analyses, including those of other ocean regions, are needed to support their findings.

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