The last time CO2 levels were so high, sea level was higher and Antarctica had trees – ThinkProgress

The last time carbon dioxide levels in the atmosphere were as high as today, the sea level was 60 feet higher and it was so hot that trees were growing in Antarctica.

According to the most detailed global climate reconstruction carried out by researchers at the Potsdam Institute for Climate Impact Research (PIK), current CO2 levels of 410 parts per million (ppm) have been observed for last time 3 million years ago. They have been published in Science Advances.

Their in-depth analysis of fossils and plant sediments reveals that such CO2 levels were last seen in the Late Pliocene, at a time when no ice cover covered either Greenland or West Antarctica and where much of of the eastern Antarctic ice sheet had disappeared. Temperatures reached 7 degrees Fahrenheit worldwide, at least double that of the poles, and sea level was about 20 meters higher.

"This is an amazing discovery," Jane Francis, director of the British Antarctic Survey, told The UK Guardian. "They found fossil leaves of southern beech. I call them the last forests of Antarctica. "

Although the discovery is remarkable, the implications are terrible. "A sea level rise of twenty meters would have a major impact on all our coastal cities," warned Francis.

The good news is that the Earth is not warming up instantly and ice caps several kilometers thick melt even more slowly. The rise in temperature will therefore take several decades and a sea level rise of several tens of feet will take hundreds and hundreds of years. This means that the choices we make now can affect the rate of climb and determine whether we want to go beyond the 65-foot rise in sea level to more than 200 feet.

But the bad news is that every threshold of rising temperatures and sea level is almost irreversible. Therefore, in the absence of a very aggressive action over the next decade, the rise in sea level will be unachievable.

Even worse, the climate policy agenda advocated by President Donald Trump – measures such as the retreat of US laws reducing carbon pollution and the abandonment of the Paris agreement on the climate – would lock us into CO2 levels so high that the sea level would rise by one foot per decade. just a few decades.

One aspect of the study that has not received much attention is the discovery by researchers that the Earth's climate is very sensitive to small changes in CO2 levels.

"The role of CO2 changes in the formation of ice cycles has not been fully understood," said lead author Matteo Willeit of PIK. "This is a breakthrough that we can now show … that changes in CO2 levels have been the main factor in glaciation, as well as changes in the Earth's rotation around the sun, Milankovitch cycles."

Once again, their remarkable discovery is also quite disturbing for the inhabitants of Earth today. "Our results imply a high sensitivity of the Earth's system to relatively small variations in atmospheric CO2," said Willeit. "As fascinating as it may be, it is also disturbing."

The fact that the Earth's climate shows a high sensitivity to CO2 levels is particularly worrying as it means that we are much more likely to face the worst-case scenario with respect to the impacts of climate change. And it is therefore all the more urgent that the countries of the world immediately reduce carbon pollution and limit as much as possible the increase of atmospheric CO2.