(CN) — In the wake of the grim United Nations report on the irreversible consequences of climate change, Massachusetts Institute of Technology researchers are shining a light on a principle spanning tens of millions of years believed to have made things worse in the past: global warming begets more warming.
Constantin Arnscheidt, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences, and his team conducted their study using the paleoclimate data from the past 66 million years — beginning just after dinosaurs went extinct.
They did this by studying single-celled organisms called benthic foraminifera that have existed for hundreds of millions of years, preserved in deep-sea sediments. Temperature changes the composition of the organisms’ shells, making them a dependable subject for time traveling to define Earth’s temperatures in ancient history.
While most past studies of the organisms have been used to look at large spikes in temperature, the MIT researchers focused on overall trends and fluctuations over time. Using statistical analyses, they parsed out the more extreme warming periods from the less frequent, and less intense, cooling periods over the past 66 million years.
The data shows that periods of prolonged global warming were both more frequent and more severe on the geologic timescale as compared with periods in which the Earth got cooler. As for why, consider how a multiplier effect in a casino slot machine brings a bigger payout. Just as volcanoes release carbon dioxide that, in turn, contributes to warmer temperatures overall, Wednesday's study says small amounts of warming can lead to a compounding effect.
“Everything’s pointing to something fundamental that’s causing this push, or bias toward warming events,” Arnscheidt said in remarks released along with the research.
To confirm the existence of bias, and not simply “noise” in the data, that would makes the climate more volatile overall, the team looked at the correlation between temperature fluctuations and Earth’s orbit. In the long term, over hundreds of thousands of years, the planet’s path around the sun has become less elliptical.
The change in orbit seems to coincide with past warming events — but does not explain why warming tends to be more extreme than cooling.
So the MIT team used a set of mathematical equations that describe multiplier effects like the one they observed, testing and confirming their theory of how atmospheric warming is amplified.
It took the formation of ice sheets in the Northern Hemisphere about 5 million years ago to reduce the multiplier effect of the last warming period. With those frozen masses receding today, however, the Earth confronts a threat that the multiplier effect could return.
Publishing their results Wednesday in the journal Science Advances, the MIT team say the data suggests that the planet could, in the future, be more susceptible to the extreme warming episodes of the geologic past.
“The Northern Hemisphere’s ice sheets are shrinking, and could potentially disappear as a long-term consequence of human actions,” Arnscheidt said.
More extreme weather events — drought, floods, wildfires and the like — have alarmed the public and scientists alike. Those events place the study into context, as the public continues grappling with the latest report from the U.N.'s Intergovernmental Panel on Climate Change, which warns of "irreversible" sea level rise and other "unprecedented changes."
“Humans are forcing the system in a new way,” Arnscheidt said. “And this study is showing that, when we increase temperature, we’re likely going to interact with these natural, amplifying effects.”
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