Paleoclimatologists James Zachos (University of California at Santa Cruz, USA) and Ellen Thomas (Yale University and Wesleyan University, USA) identified an anomalous episode in the planet’s history in which massive emissions of CO2 into the atmosphere occurred, causing a global temperature rise of between 5 and 6 ºC and a massive extinction of species in the deep ocean, which has provided “a very valuable analogy of anthropogenic climate change”, according to the jury of the BBVA Foundation Frontiers of Knowledge Award in Climate Change.
The greenhouse effect caused by what is now referred to as the Paleo-Eocene Thermal Maximum (PETM) is comparable to today’s climate change caused by fossil fuel combustion, lending weight to the numerical models currently in use to predict future climate evolution.
This episode, which occurred 56 million years ago, probably provoked by volcanic activity, turned the oceans more acidic and unleashed one of the biggest extinctions of deep-sea fauna in the whole history of Earth.
The PETM is considered the best historical analog for modern climate change. It is in this sense a kind of “natural experiment” that has served to validate and bound the models currently in use to predict future climate development, remarked Professor Zachos in an interview shortly after hearing of the award.
A serendipitous discovery
The discovery of PETM had its beginnings in a 1987 drilling expedition to the Antarctic Ocean, with Ellen Thomas, researcher at Yale University, among its crew, and it happened, the awardee relates, out of “serendipity.” Her job on board was to analyze the sediment samples obtained in search of benthic foraminifera, microscopic organisms that live on the ocean floor.
However, Thomas observed a truly surprising mass extinction in such a stable environment, so it could only be due to dramatic change on a global scale. “It was not at all what I expected,” she recalls. “It was the largest extinction of deep-sea fauna within the last 90 million years,” explains Laia Alegret, Professor of Paleontology at the University of Zaragoza and a member of the Spanish Royal Academy of Exact, Physical and Natural Sciences, who nominated the researchers for the Frontiers of Knowledge Award.
Ellen Thomas, BBVA Foundation Frontiers of Knowledge Award in Climate Change in 2023. - Fundación BBVA
Shortly thereafter, definitive confirmation of this phenomenon came from James Zachos’ research on terrestrial sediments obtained in Wyoming (USA). “What Thomas had found in the deep sea, Zachos was now observing on land thousands of kilometers away. This was proof that what they were looking at was a major global event, affecting not just terrestrial systems but also the ocean floor and surface,” explains Alegret.
“Suddenly all the pieces of the jigsaw started to fall into place, and they were also consistent with the greenhouse effect theory,” Zachos relates.
The historical knowledge provided by Zachos and Thomas has been fed back into predictive models for the impact of present-day climate change to test the soundness of their forecasts. “We have been able to confirm that the greenhouse effect theory is essentially correct,” says Zachos, “and this has made us more confident about our ability to predict future climate.”
James Zachos, BBVA Foundation Frontiers of Knowledge Award in Climate Change in 2023. - Fundación BBVA
CO2 capture with new technology
The droughts and severe rainfall episodes that are part of climate change as we are currently experiencing it reflect changes in the hydrologic cycle which have also been documented during the PETM. Not only that, but this episode has also confirmed that it takes tens of thousands of years for excess carbon in the atmosphere to be sequestered by natural processes. For the awardee researchers, this finding proves that we cannot rely solely on forests to absorb the carbon emitted by burning fossil fuels as a solution to the current crisis.
Zachos, in fact, would like to see the process speeded up by recourse to technologies that capture atmospheric CO2 so it can be buried where it will not produce any greenhouse effect. Carbon is already being injected into the Earth’s crust and some propose doing the same in the ocean, while plans have been mooted to accelerate the decomposition of rocks or even to pulverize them for worldwide use as a fertilizing agent.
“All these actions, taken together, could start removing CO2 from the atmosphere at a relatively fast rate,” says the award-winning researcher.
Unavoidable effects: Sea-level rise and major droughts
Asked whether today’s human-induced greenhouse effect could end up triggering a warming event as extreme as that suffered during the PETM, Zachos believes that “it could easily happen” if we go on burning fossil fuels and sticking to the familiar but pernicious routine of “business as usual.”
However, the laureate is convinced we still have time to remedy the situation, or at least to avert its worst consequences. He warns that certain impacts are “probably unavoidable,” for instance, that “we are already committed to a meter or two of sea-level rise even if we could cut carbon emissions immediately.” Nonetheless, he believes, “we still have the opportunity to prevent the worst-case scenarios if we can reverse or reduce carbon emissions, so we don’t end up with sea-level rise of 10 to 15 meters.”
Thomas, meantime, admits to feeling “fairly pessimistic” about stopping global warming from causing grave harm to the human population: “Regarding sea level, for example, I am pretty much convinced that we have underestimated the rate of increase, and will see serious effects in populated areas, like my own country of birth, the Netherlands, where large expanses may end up underwater, along with large parts of New York and Florida. People will have no choice but to emigrate.”
Thomas is likewise especially concerned about the impacts of warming on the hydrologic cycle, as shown in records for the PETM, and how they may affect agriculture: “Many zones will dry up and will no longer be suitable for major food crops.”
“The reality,” concludes Thomas, “is that the anti-climate change measures taken to date are wholly insufficient. I don’t want to sound alarmist, but I do think we are in serious trouble, not for the planet – which will go on without us – but for ourselves, who need to change our way of life very quickly.”