Earth’s Oceans Used To Be 20-25°C Warmer Than They Are Today

By: - Climate DepotOctober 5, 2020 12:32 PM

Earth’s Oceans Used To Be 20-25°C Warmer Than They Are TodayNoTricksZone: Not here to worship what i… / by Kenneth Richard / 

Today’s global ocean temperatures hover around 15°C on average. About 400 to 500 million years ago, Earth’s ocean temperatures averaged 35-40°C and atmospheric CO2 concentrations were “5-10x higher than present day values” (Henke et al., 2018). During this period, the marine biosphere thrived (Voosen et al., 2019).

Image Source: Henke et al., 2018
Image Source: Voosen et al., 2019 and press release

During the last 5.4 million years, CO2 has varied between 180 and 500 ppm (Fletcher et al., 2019). During the Pliocene (5.4 to 2.5 million years ago), Arctic temperatures were said to have been 22°C warmer than today (Fletcher et al., 2017) and tropical ocean temperatures were 3-6°C warmer than present (Wycech et al., 2020).

Image Source: Fletcher et al., 2019
Image Source: Fletcher et al., 2017
Image Source: Wycech et al., 2020

During the peak of the last glacial (the Last Glacial Maximum) 19,000 years ago, the Southern Ocean was 2°C warmer than it is today even though CO2 levels were a dangerously low 180 ppm at this time. This was also the same period when the Earth’s bottom water temperatures warmed up by about 2°C 1,000 years before the oceans’ surface began warming and CO2 began to rise (Stott et al., 2007).

Image Source: Stott et al., 2007

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

Global ocean temperatures were still warmer than today througout nearly all of the last 10,000 years (Rosenthal et al., 2017), including the Medieval Warm Period (Gebbie and Huybers, 2019).

Image Source: Rosenthal et al., 2017
Image Source: Gebbie and Huybers, 2019

In sum, paleoclimate research strongly suggests there is nothing unprecedented or even unusual about ocean temperature changes in the modern era.Donate – choose an amount