A study warned that global temperatures by the end of the century will reach levels not seen in 50 million years if greenhouse gas emissions are not significantly reduced.
German and American experts analyzed small fossils in samples dug from the sea floor, to reconstruct the Earth’s climate history back to the time of the dinosaurs.
During this 66 million years period, the planet has witnessed four distinct climatic states – which scientists have called “greenhouse”, “warm habitat”, “coolant” and “ice habitat”.
For most of the past three million years, the Earth has been in an “icy” state characterized by alternations between ice ages and ice periods.
However, experts warn that greenhouse gas emissions and other human activities are now pushing the climate towards a “greenhouse”.
The warm habitat conditions were last seen during the Eocene – which ended about 34 million years ago – when there were no polar ice caps.
During this time, global average temperatures were 16.2-25.2 degrees Fahrenheit (9-14 degrees Celsius), higher than at present.
The author of the paper, James Zakos, said that the Intergovernmental Panel on Climate Change projections for 2300 in the “business as usual” scenario [emissions] say that it is likely to raise global temperature to a level not seen in the planet 50 million years ago. “
In their study, Professor Zakos and colleagues created a “climate reference curve” called CENOGRID, which maps global temperature changes in the past and in the present, and includes different forecasts for the future based on emissions levels.
CENOGRID revealed that the natural climate variability, which occurs as a result of changes in the Earth’s orbit around the sun, is much smaller than the expected future warming due to greenhouse gas emissions.
Marine geologist Thomas Westerhold said: “We now know more precisely when the atmosphere is warmer or colder, and we have a better understanding of the basic dynamics and the processes that drive them.”
“The time from 66 to 34 million years – when the planet was noticeably warmer than it is today – is especially important, because in the past it represents what human change could lead to in the future,” he added.
Professor Zakos, who is conducting research at the University of California, Santa Cruz, said: “We have known for a long time that interglacial cycles follow at the pace of changes in Earth’s orbit.” These cycles change the amount of solar energy that reaches the surface of the Earth, and astronomers have been computing these orbital changes through time, he said. And when we reconstruct past climates, we can see extreme long-term changes well. We also knew that there had to be a variation. Rhythmic changes due to orbital changes, but for a long time it was impossible to recover that signal. Now that we have succeeded in recognizing natural climate variability, we can see that the expected anthropogenic warming will be much greater than that. “
Most of the major climate shifts in the past 66 million years – when a giant asteroid killed the dinosaurs – have been linked to changes in levels of greenhouse gases.
Previous research by Professor Zakos found that the period of rapid global warming about 50 million years ago, which pushed the climate into a greenhouse, was the result of a massive release of carbon into the atmosphere.
Likewise, in the late Eocene period, as atmospheric carbon dioxide levels decreased, ice sheets began to form in Antarctica and the climate shifted to a cooling state.
“The climate can become unstable when it approaches one of these shifts, and we see less predictable responses to the orbital forcing, so we want to understand it better,” Zakos added.