It's already too late.

Even if humanity manages to limit warming to 1.5 ° C compared to the pre-industrial era, which is the target by 2100, sea levels will rise for centuries, warned on Tuesday. scientists.

Most current estimates of sea level rise and the threats it poses to coastal cities run to the turn of the century and range from half a meter to less than a meter.

But the phenomenon will continue beyond 2100 under the effect of warming water and melting ice, regardless of the speed of reduction in greenhouse gas emissions. We can already observe it at the permafrost level, in the arctic regions: the increase in temperature first causes a slight melting. Then, by what one could ironically qualify as a “snowball effect”, the contact of this light layer of water at room temperature with the ice, combined with the release of greenhouse gases contained in the permafrost, will again melt the latter.

"About 5% of the world's population currently lives on land below the level that will be reached at high tide under the effect of carbon dioxide already accumulated in the atmosphere by human activity," Ben told AFP. Strauss, lead author of the study published in the journal Environmental Research Letters.

Current conditions are sufficient to raise sea levels by nearly two meters, whether it takes two centuries or ten centuries, he estimates.

Nine Asian mega-cities under threat

At least half a billion people would be affected by this direct rise in sea level and the resulting floods, but also more vulnerable to storms.

Asia, which has nine of the ten highest-risk mega-cities, will be the hardest hit.

The fight can almost seem lost in advance.

The 1.5-degree limit enshrined in the Paris Agreement that countries around the world will try to maintain at the COP26 summit in Glasgow next month translates into a rise in water levels of nearly three meters in the long term.

"In Glasgow and until the end of this decade we have the possibility either to help the next hundred generations or to betray them", concludes Ben Strauss.

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