Washington (AFP)

The Earth is such a complex system that it is difficult to predict how much the oceans will rise due to global warming by the end of the century. In a study published Monday, 22 experts give their estimates, and the worst exceed the current scientific consensus.

The latest baseline estimate by the Intergovernmental Panel on Climate Change (IPCC) in 2014 estimated the worst case scenario at just under one meter of sea level rise at the end of the 21st century, compared to the period 1986-2005.

The study published Monday in the minutes of the American Academy of Sciences (PNAS) does not contradict this possible scenario, but warns that there is a significant probability that the rise is more serious: their median prediction is 69 cm in an optimistic scheme, and 111 cm in the current trajectory, compared to 2000.

The optimistic scenario is a global warming of 2 ° C compared to the pre-industrial era (late nineteenth century): this is the minimum objective of the Paris agreement, signed in 2015. The Earth s has already warmed by around 1 ° C since that time.

The pessimistic scenario is a warming of 5 ° C, which corresponds to the current unimpeded trajectory of greenhouse gas emissions by human activities.

But the possible amplitude of the rise of the oceans, according to the experts who took part in the study, is very great: even if humanity managed to limit the increase of the temperature of the globe to 2 ° C, the rise could vary between 36 and 126 cm (5 to 95% probability range). And if 5 ° C rise, there is a risk of 5% that the increase exceeds 238 cm.

The study is an assembly of 22 expert estimates of the ice caps of Greenland and Antarctica. Melting ice is one of the main factors in rising water levels, with glaciers (ice rivers) and thermal expansion of the oceans (warm water is gaining volume) - but it is also the most unpredictable, and this is where expert models have progressed in recent years.

"We conclude that it is plausible that the rise in sea level will exceed two meters by 2100 in our high temperature scenario," the authors write.

This would mean the loss of 1.79 million square kilometers of land, and the displacement of 187 million people, according to them.

"Rising seas of this magnitude would have profound consequences for humanity," warns lead author Jonathan Bamber, a professor at Bristol University.

? 2019 AFP