Repères 01/06/08 - Scénario catastrophe pour le climat

Une nouvelle étude publiée jeudi par la prestigieuse revue scientifique Nature présente le pire scénario d’emballement de l’évolution du climat dans lequel la Terre pourrait perdre la totalité de ses glaces en l’espace d’une génération.

Si la température du globe continue d’augmenter, d’énormes quantités de méthane pourraient être libérées par les 10 000 gigatonnes de gaz gelé qui sont à l’heure actuelles emprisonnées dans les profondeurs des océans et le pergélisol. Le franchissement de ce seuil de basculement du climat aurait pour conséquence que le réchauffement de la planète serait alors bien pire et plus rapide que ce qu’envisagent aujourd’hui les prévisions des scientifiques...

 

Could Methane Trigger a Climate Doomsday Within a Human Lifespan?
Wired May 28, 2008

"A new paper published appearing Thursday in the prestigious scientific journal Nature presents the worst-case scenario for runaway climate change that could leave the Earth entirely ice-free within a generation.

If global temperatures continue to rise, massive amounts of methane gas could be released from the 10,000 gigaton reserves of frozen methane that are currently locked in the world's deep oceans and permafrost. Passing this climate tipping point would result in global warming that would be far worse and more rapid than scientists' current estimates.

The new paper suggests that exactly this type of cascading release of methane reserves rapidly warmed the Earth 635 million years ago, replacing an Ice Age with a period of tropical heat. The study's lead author suggests it could happen again, and fast -- not over thousands or millions of years, but possibly within a century.

"This is a major concern because it’s possible that only a little warming can unleash this trapped methane," Martin Kennedy, a professor at UC Riverside, said in a release. "Unzippering the methane reservoir could potentially warm the Earth tens of degrees, and the mechanism could be geologically very rapid."

Methane is 25 times more potent than carbon dioxide as a greenhouse gas. And the frozen reserve is twice as large, by volume, as the world's known fossil fuel reserves.

Climate projections, like those produced by the Nobel Prize-winning Intergovernmental Panel on Climate Change, usually look like smooth lines moving up steadily along with carbon dioxide levels, which is a reflection of the linear mathematical models that underpin the graphs. But Kennedy and other geologists, while accepting the importance of anthropogenic greenhouse gas emissions, say that standard climate models can't account for massive climate changes that occur within decades. 

"None of this stuff is linear. It's non-linear," Kennedy said..."..."

 

Voir :

Snowball Earth termination by destabilization of equatorial permafrost methane clathrate
Martin Kennedy, David Mrofka & Chris von der Borch, Nature 453, 642-645 (29 May 2008)