A new study finds Earth’s bottom water temperatures (BWTs) have cooled by 2-3°C over the last 4.5 million years through to the pre-industrial era (1750).

Since 1750, however, global BWTs have not risen in a detectable way, nor have they exceeded the warmth achieved during the Medieval Warm Period (Gebbie and Huybers, 2019). The Pacific Ocean as a whole has continued to cool in the last centuries.

Image Source: Clark et al., 2025 and Gebbie and Huybers, 2019

Regionally, today’s North Atlantic’s bottom water temperatures hover around 4°C – just as they did throughout the Late Holocene. The BWTs averaged ~5°C, or “slightly warmer than present-day,” during the last glacial, with anomalies reaching 10°C both 13 and 16 thousand years ago and about 7°C both 15 and 19 thousand years ago (Yasuhara et al., 2019).

Image Source: Yasuhara et al., 2019

As recently as 10,000 years ago, the Arctic Ocean’s bottom water temperatures were 6-10°C warmer than they are today (Beierlein et al., 2015).

Image Source: Beierlein et al., 2015

These global and regional BWT reconstructions do not support the narrative that modern ocean temperatures are unprecedentedly warm due to human activity.