CO2 at 3 million years

The carbon dioxide that warms the planet in the Earth's atmosphere – at its highest level in three million years – is poised to contain a dramatic temperature and sea-level rise over several centuries, warned scientists this week.

The last time CO2 reached 400 parts per million (ppm), Greenland was ice-free and trees were growing on the edge of Antarctica.

It has long been thought that current levels of greenhouse gases are not higher than those of 800,000 years ago, during a period of cyclical global warming and cooling that would likely have continued without anthropogenic emissions.

However, analyzes of ice cores and ocean sediments in the coldest region of the planet have revealed that the last zone of 400 ppm was exceeded three million years ago in the upper Pliocene when temperatures exceeded several degrees Celsius and the oceans of at least 15 meters.

At the same time, advanced climate modeling by experts from the Potsdam Institute for Climate Impact Research (PIK) is directly correlated to the CO2 levels present in these Antarctic samples.

"The end of the Pliocene is relatively close to us in terms of CO2 levels," AFP member Matteo Willeit told AFP and lead author of the study.

"Our models suggest that there were no glacial cycles – there were no large ice caps in the northern hemisphere, the CO2 was too high and the climate was too high. hot to allow the growth of large ice caps. "

In 2015, nations signed the Paris agreement on climate change, promising to reduce greenhouse gas emissions and limit the rise in temperature to "well below" 2 Celsius (3, 6 Fahrenheit).

Yet, in 2017, emission levels have not been exceeded in human history, and climate experts warn that time has stopped to drastically reduce fossil fuel consumption and prevent global warming. unbearable climate.

Seas 15-20 meters higher

Scientists met this week in London for a conference on the Pliocene era and highlighted the lessons learned today embedded in its old samples of ice and sediment.

"The news is that temperatures were 3 to 4 degrees higher than today in the world and that the sea level was 15 to 20 meters higher," Martin told reporters. Siegert, professor of geoscience at Imperial College London.

With only 1 ° C warming up to now, the Earth is already struggling with floods, droughts and super storms aggravated by rising seas.

Siegert said that 400 ppm did not mean that the severity of Pliocene sea level rise was imminent. But unless humans find a way to massively extract CO2 from the air, serious impacts are inevitable sooner or later.

"There is a gap," he explained. "If you light the oven at home and set it at 200 ° C, it does not reach that level immediately, it's the same for the climate."

Siegert said that glaciologists, based on current CO2 concentrations, expect a sea level rise of 50 centimeters to one meter during this century.

"It would be difficult for it to be much more than that because it takes time to melt," he added.

"But it does not stop at 9pm, it goes on."

An accelerated rate of CO2

In October, the UN concluded that greenhouse gas emissions would halve by about 12 years to maintain a chance to limit global warming to 1.5 ° C, the level needed to avoid serious impacts on the climate.

But despite these earlier warnings, CO2 emissions from the use of fossil fuels, construction, aviation and agribusiness continue to rise and are poised to heat up. the planet 4C by the end of the century.

Even without additional carbon pollution, the outlook remains bleak.

"If we stay at 400 ppm, we continue on the path of a Pliocene-like climate," said Tina van De Flierdt, professor of isotope geochemistry at Imperial Oil.

She warned that, in conditions similar to those of today, the Pliocene has seen the Greenland icecap disappear, which today contains enough frozen water to lift the sea ​​level of some seven meters in the world.

"The ice cap of West Antarctica has a height of about 5 meters – she was probably gone," she added.

Like what is happening today, the Earth's poles have warmed up much faster than the rest of the planet at Pliocene, have shown earlier research, including a study on Nature Climate change.

In previous periods, the Earth had seen sustained concentrations of carbon dioxide above 400 ppm, but it took millions of years for these increases to occur.

Emissions of greenhouse gases caused by humans, by contrast, have increased CO2 levels by more than 40% in just over 150 years.

"A crazy experience"

At 412 ppm and up, the experts said the temperature rises of 3-4 ° C are probably now blocked.

So what happened to Earth the last time CO2 was so prevalent?

It was captured in trees, plants, animals and minerals alive at the time and buried under the ground when they died.

"And what we have been doing for 150 years is to dig everything up and put it back into the atmosphere," Siegert said.

"It's like a crazy experiment: take this CO2 that took 100 million years to be sequestered and put back in the atmosphere instantly to see what happens."

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© 2019 AFP