A lesson from the past

PETM Foram

If you’re a regular reader of this blog you might have heard of Dr Tracy Aze already, and may even recognise the strangely-shaped specimen above as an example of planktonic foraminifera, the single-celled marine organisms that Tracy has been researching. This morning we have issued a press release about Tracy’s research which offers a warning from history about carbon emissions and global warming.

Surprisingly enough, the study shows how the fossils of these creatures hold clues to the impact on our oceans of man-made global warming. Around 56 million years ago, in a period known as the Palaeocene-Eocene Thermal Maximum (PETM), a rapid rise in greenhouse gases caused sea surface temperatures to rise as high as 40°C, with significant impacts on marine life.

Worryingly, the PETM – which lasted for around 170,000 years – saw the release of roughly the same volume of CO2 as expected from modern fossil fuel consumption. Tracy explains:

The amount of CO2 that is predicted to be released from the Industrial Revolution to around 100 years from now is roughly equivalent to what happened in the PETM. But the big difference is the rate of release: today we are releasing greenhouse gases at a far faster rate than 56 million years ago.

Although the research was conducted by Tracy, the project was led by Professor Paul Pearson of Cardiff University and funded by the UK Ocean Acidification research programme.

Tracy and her team used newly-extracted planktonic foraminifera fossils from Tanzania, dating from the PETM period. The tiny shells of these organisms contain different proportions of oxygen isotopes and these proportions are largely determined by the sea temperatures at the time. So the fossil shells offer a glimpse of the way sea temperatures were rising alongside the release of greenhouse gases, as well as a record of the relative abundance of this planktonic life in the oceans.

The PETM shows us that rapid increases in CO2 in the atmosphere have significant impacts on global temperatures, with the new information from our study site showing that tropical sea surface temperatures may have exceeded 40°C with an associated local disappearance of marine life.

The research paper, Extreme warming of tropical waters during the Paleocene–Eocene Thermal Maximum, was published in the September issue of Geology and is available as open-access.

Scott Billings – Public engagement officer



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