Published this week in the journal Nature, the study in question was carried out by Australian and American researchers. They analysed the skeletons of Caribbean sclerosponges, which are composed of calcium carbonate and have the ability to preserve a record of palaeotemperature.

The value of studying marine species such as sclerosponges lies in the fact that they have been around for centuries (long before the industrial era).

“Increasing ocean and land-air temperatures overlap until the late twentieth century, when the land began warming at nearly twice the rate of the surface oceans,” notes the study.

The results also point to a 0.5°C rise in temperature and a 2°C global warming forecast for the late 2020s, “nearly two decades earlier than expected.”

“[T]he overriding aim of the UN Paris agreement to keep the combined land and ocean global surface temperature increase to below 2 °C is now a much greater challenge, emphasising the even more urgent need to halve emissions by 2030,” the scientists conclude.

The results of this research, however, have yet to be validated by the scientific community, especially as it has several limitations, not least of which is its focus on a specific region (the sclerosponge skeletons were collected in Puerto Rico), a much more restricted perimeter than the temperature measurements, taken by boat, on which the IPCC estimates are based. However, this is not the first study to suggest an earlier start to global warming.

In 2016, an international team of researchers published a study, again in the journal Nature, suggesting that temperature rises linked to human activities appeared in the Northern Hemisphere as early as the 1830s.