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

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.

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.

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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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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