(CNN) – The last time carbon dioxide levels were so high, Greenland was mostly green, sea levels were up to 20 meters higher and trees grew in Antarctica, according to scientists who warned this week that there is more CO2 in our atmosphere today than in the last three million years.
Using a new computer simulation, researchers at the Potsdam Institute for Climate Impact Research (PIK) in Germany, found that the last time the Earth's atmosphere had a CO2 concentration as high as it is today was during the Pliocene era , the geologic period 2.6-5.3 Millions of years ago.
CO2 emissions from human activities are the main cause of climate change.
The amount of CO2 in the atmosphere today is "unnatural," senior author Matteo Willeit told CNN.
Willeit said that, according to the simulation, CO2 levels should not be higher than 280 parts per million (ppm) without human activity, but are currently 410 ppm and are increasing.
Average global temperatures are rising much faster than at any time since the Pliocene, Willeit added.
At that time, they have never exceeded pre-industrial levels by more than 2 ° C, but current models show that temperatures will rise by 4 ° C between 2000 and 2100 if no measures are taken to reduce emissions, he said.
In unknown territory
Willeit said that the increase in CO2 levels is driving the Earth beyond the climatic conditions experienced by humans.
If levels and temperatures of CO2 continue to rise, "our planet will change" and sea levels will increase by one or two meters in the next 200 years, he added.
This research is not the first to suggest that current levels of CO2 are the highest since the Pliocene, but Potsdam researchers say that their work is the first to combine the ocean bottom sediment data with the badysis of volumes of ice past, and it is more sophisticated than other model studies.
Scientists at a meeting of the Royal Meteorological Society on the climate of the Pliocene in London on Wednesday discussed how sedimentary records and fossils of nearby Antarctic plants show that during the Pliocene era, summer temperatures in the Arctic were 14 ° C higher than the current ones.
Professor Martin Siegert of Imperial College London, speaking at the event, said the findings offered a glimpse into the future of the Earth if drastic measures are not taken to address global warming.
This story was first published on CNN.com "Highest CO2 levels for 3 million years: when the seas were 20 meters higher"