Greenhouse gas emissions caused by anthropogenic climate change are currently warming the planet at a much faster rate than the most rapid warming events of the Phanerozoic, the last 540 million years of geological time, according to a new study published Thursday in the journal Sciencewhich provides the most complete reconstruction to date of the Earth’s surface temperature over the past 485 million years.
The new curve reveals that the Earth’s temperature has varied more than previously thought over this period, and confirms that these variations are strongly correlated with the amount of carbon dioxide in the atmosphere. And it shows that, while it has been much warmer at times in Earth’s past, an acceleration as pronounced as the one we are experiencing has never been experienced, on a scale of decades.
The study’s authors, led by the Smithsonian Institution and the University of Arizona, generated this temperature curve using a method called data assimilation, which allowed them to combine geological records and climate models to create a more coherent understanding of ancient climates.
“Adapted to a cold climate”
A detailed analysis of how Earth’s temperature has fluctuated over time provides crucial context for understanding modern climate change, the authors point out. What they found is that throughout the Phanerozoic, the planet’s average surface temperature ranged between 11 and 36°C, and periods of extreme heat were linked, in most cases, to high levels of carbon dioxide in the atmosphere.
“This research clearly illustrates that carbon dioxide is the dominant factor in controlling global temperatures over geological time,” he says. Jessica Tierneypaleoclimatologist at the University of Arizona and co-author of the paper. “When CO2 is low, the temperature is cold; when CO2 is high, the temperature is warm.”
We are adapted to a cold climate. It is dangerous to rush to a warmer climate.
Jessica Tierney
— Paleoclimatologist at the University of Arizona and co-author of the article
The results also reveal that Earth’s current global average temperature, at 15°C, is colder than it was for much of the Phanerozoic. In other words, we’re in a kind of privileged pause in the planet’s history that we could be ruining by our behavior. Because greenhouse gas emissions caused by anthropogenic climate change are currently warming the planet at a much faster rate than during the warmest moments of the Phanerozoic—not reassuring, given that those episodes of rapid climate change caused mass extinctions.
“Humans and the species we share the planet with are adapted to a cold climate,” Tierney says. “It’s dangerous to quickly push us back to a warmer climate.”
A gigantic puzzle
The fragmentary nature of the fossil record makes reconstructing past temperatures far from simple. Some specimens, such as fossilized palm fronds found in Alaska, are useful pieces that provide evidence of a period in Earth’s past when global temperatures were much warmer than today. “It’s like trying to visualize the image of a 1,000-piece jigsaw puzzle when you only have a handful,” says Emily Judd, lead author of the new paper.
To create an accurate curve, the team reconstructed snapshots of the world’s climate at various points in the Phanerozoic by integrating data on ancient ocean temperatures from different parts of the planet with computer simulations of past climates. They also collected more than 150,000 published data points from five different geochemical archives (or “proxies”) for ancient ocean temperatures preserved in fossilized shells and other types of ancient organic matter. And colleagues at the University of Bristol generated more than 850 simulations of what Earth’s climate might have been like at different times in the distant past, based on the position of the continents and atmospheric composition.
The researchers then used data assimilation to combine these two pieces of evidence and create a more accurate curve of how Earth’s temperature has changed over the past 485 million years. “We all agree that this is not the final curve,” said Brian Huber, a co-author of the paper. “Researchers will continue to uncover additional clues about the distant past that will help revise this curve in the future.”
“This will not give us time to adapt”
José Javier Álvaro Blasco, a researcher at IGEO-CSIC, believes that this is a formidable work, in which the authors have gathered an immense amount of prior information. “The analysis indicates that temperature (and climate) fluctuations in the past have been much greater and that more extreme values have been reached than those estimated so far,” he explains to elDiario.es. “The problem is that past climate fluctuations were measured over hundreds of thousands, even millions of years, and current global warming is already measured over decades.”
For me, the result leaves a main message: with the speed at which the temperature is increasing, human beings will not have time to adapt.
Ana Moreno
— Paleoclimatologist at the CSIC of the Pyrenees Institute of Ecology (IPE)
Javier Martín Chivelet, from the Institute of Geosciences (CSIC-UCM), considers that this is a very interesting work that presents significant differences with previous reconstructions based only on paleoclimatic data, which will undoubtedly open new scientific debates. Regarding the analogy with current climate change, let us remember that the most rapid changes are not reflected in the new reconstruction due to a resolution problem, which represents a significant limitation. “This produces the very jagged and periodic effect of the curve, which I am convinced will open intense debates,” he says.
“It is important to remember that the study is not made to compare the past with the current situation, because the scale has nothing to do with it, although things can be extracted, such as the relationship between temperature and CO2,” emphasizes Ana Moreno, paleoclimatologist at the CSIC of the Pyrenean Institute of Ecology (IPE). The authors themselves find this relationship on this time scale between temperature and carbon dioxide surprising, they emphasize, since there are many other factors that they believe would be important, such as changes in the luminosity of the sun. “For me, the result leaves a main message: with the speed at which the temperature is increasing, human beings will not have time to adapt,” he emphasizes.
“The planet has been warmer than today on several occasions, but the rate of warming is now much faster than at other times,” says Samuel Zamora, a paleontologist and expert in marine invertebrates at the Geological and Mining Institute (IGME-CSIC). The fact that the temperature curve proposed by the new study is moving towards colder temperatures should not confuse us, he warns, because if we were to bring the magnifying glass closer to the final section – on a scale of decades – we would see a sharp increase. “We must take into account the speed of the changes, which will make many regions uninhabitable for us.”
Isabel Cacho, a professor at the University of Barcelona (UB) and a specialist in the reconstruction of climate variability from marine sediments and cave speleothems, considers the result to be very valuable, as it is the first serious and concise work that extends the temperature curve beyond the last 65 million years, which is all that we have covered so far. “We already knew that the planet had been warmer than colder, but here they allow us to install units,” he says. He agrees that some will be tempted to use this to say that, since the planet has already experienced warmer periods in the past, there is no need to worry. “But be careful, the speed with which these changes are occurring now greatly compromises the adaptive capacity of the species that live at this time and in these conditions.”
We are experiencing the most exaggerated temperature acceleration since the Phanerozoic and, probably, in the history of the Earth.
Jose Javier Alvaro Blasco
— IGEO-CSIC Researcher
“We see that the Earth has been systematically in cold conditions when CO2 was low and vice versa,” Cacho says. That doesn’t mean there is causality, he cautions, but carbon dioxide has always been a feedback factor. “It has always gone hand in hand with the planet, we know that if we go up, it warms up and that is indisputable with the geological record,” he says. “And the levels we have today are already higher than any values that have existed throughout human history,” he says.
“We are experiencing the most exaggerated temperature acceleration since the Phanerozoic and, probably, in the history of the Earth,” concludes Álvaro Blasco. “No animal or plant can adapt to the current rate of environmental changes: our genetics are not enough.”
