Point de non retour

e360 est un nouveau site environnemental anglais.

[e360] New scientific evidence suggests that we have already passed a dangerous threshold for the amount of carbon dioxide in the atmosphere – and that the time for taking bold action is slipping away.

by bill mckibben

As the Bush administration starts to pass from the scene and the contenders to succeed him speak with reasonable seriousness about carbon, the question for environmentalists is going to change from: “Are we doing anything about global warming?” to “Are we doing anything near enough about global warming?” Both of those are political questions — but the second one is also a scientific query, for the answer to it depends on knowing how much we need to do.

The shorthand answer to that (and the one number you need to know to understand the 21st century) is: 350, as in 350 parts per million of carbon dioxide in the atmosphere.

The longer answer goes like this. Twenty years ago, when we started worrying about what we then called the greenhouse effect, we had only the crudest notion of how much carbon dioxide in the atmosphere was too much. The biggest debates were about whether global warming was real, and whether or not it had already begun. It didn’t take too long — half a decade — for the Intergovernmental Panel on Climate Change to say yes to both. But the subtler questions — How immediate a problem is this? Where do the thresholds lie? — were much harder.

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