Climate change: warning of "last Antarctic forest"

Scramble on exposed rocks in the middle of Antarctica and it is possible to find the mummified twigs of shrubs that grew on the mainland about five million years ago.

This plant material does not have much to look at, but scientists say it should serve to alert the world to the possible consequences of climate change if carbon emissions are not controlled.

The period is an era that geologists call the Pliocene, 2.6-5.3 million years ago.

It was marked by significantly warmer temperatures than today, perhaps 2 to 3 degrees in the world.

These are conditions that have allowed the growth of plants even in the middle of the white continent.

The sea levels were also higher. It is uncertain of how much, but perhaps in the region of 10 to 20 m above the surface of the modern ocean.

But what's really important is that the amount of carbon dioxide in the atmosphere was very similar to what it is today – about 400 molecules of CO2 per million molecules of air.

Indeed, the Pliocene was the last time in the history of the Earth that air carries the same concentration of greenhouse gases.

And that tells you where we are going if we do not take the climate problem seriously, warns Professor Martin Siegert of the Grantham Institute at Imperial College London.

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Temperatures can currently be lower than those of the Pliocene, but that's only because there is a shift in the system, he says.

"If you put your oven at home and set it to 200 ° C, the temperature will not be at that level right now, it takes a bit of time," he told reporters.

"And it's the same thing with Earth's climate – if you raise the CO2 level to 400 parts per million (ppm), it will not suddenly be balanced overnight." It may take 300 years old or something.

"So, the question that is put to us is: what is the state of equilibrium, what will the Earth's climate look like with 400 ppm, all things settled?"

Professor Siegert was part of a group of scientists gathered Wednesday in London to discuss the Pliocene climatic lessons.

These experts want to see a lot more research on the parallels between yesterday and today.

Much of the knowledge that we currently have about the time comes from ocean sediments.

These muds, drilled off the coast of Antarctica, contain fossil organisms whose geochemistry can be used to reconstruct the ancient temperatures and the corresponding volume of ice on the planet.

If, as scientists suspect, the sea level was 10 to 20 m higher in the Pliocene, this would indicate that the ice caps also had to be very different.

"The Greenland icecap contains about 7 m (the equivalent of sea level rise) .It probably had disappeared," said Professor Tina van De Flierdt of Imperial Oil.

"In Antarctica, we have the smaller Antarctic ice cap, which is about 5 meters in size, and probably disappeared too.

"And then we have the hunk in East Antarctica, there are some parts of what people think have been stable for a very long time, but it does not work with the numbers, if we need more than 10 m sea ​​level, we need East Antarctica to be also unstable. "

This could certainly explain the presence of plants in the middle of a continent where, today, only lichens and mosses can survive.

Professor Jane Francis, director of the British Antarctic Survey, extracted her fossilized shrubs from rocks just 500 km from the South Pole.

"These are twigs similar to southern beech," she told BBC News. "I like to call them the remains of the last forests of Antarctica.

"They're probably a Pliocene age, and what we're seeing is a time when the glaciers retreated and we ended up with areas in front of these glaciers where tiny shrubs could grow. a tundra-like environment, but with enough sun in summer and temperatures up to 5 ° C. "

An unknown key is how much, how long. How fast could Antarctica retreat to the modern era if the global climate responds to forced warming of 400ppm?

The answer from Professor Rob DeConto of the University of Mbadachusetts-Amherst may be very fast.

It uses computer models that incorporate physical processes in the ice that can result in the rapid collapse of cliffs located in front of Antarctic glaciers ending in the ocean.

"Today, we measure sea level rise in millimeters per year, so a little over 3 mm per year at the present time," he said.

"But these new processes involve a potential of centimeters per year, but we are turning to geologists for advice on rates, maybe it will take 10,000 years to reach 20 meters." We still have a lot of work to do. . "

For Professor Siegert, it is imperative to control carbon emissions very quickly and then to reverse the concentration.

"Can we limit the temperature rise to 1.5 degrees during this century? Can we do it? It's possible," he says.

"We need to reduce CO2 levels to 40% of what they are today by 2030, then to zero by 2050, and then to a negative level thereafter. It's a gigantic enterprise, but it's possible. "