Three simple numbers that add up to global catastrophe:

The First Number: 2° Celsius

The Copenhagen (2009) accord did contain one important number, it formally recognized “the scientific view that the increase in global temperature should be below two degrees Celsius.” And in the very next paragraph, it declared that “we agree that deep cuts in global emissions are required… so as to hold the increase in global temperature below two degrees Celsius.”

So far, we’ve raised the average temperature of the planet just under 0.8 degrees Celsius,

The Second Number: 565 Gigatons

Scientists estimate that humans can pour roughly 565 more gigatons of carbon dioxide into the atmosphere by midcentury and still have some reasonable hope of staying below two degrees. (“Reasonable,” in this case, means four chances in five, or somewhat worse odds than playing Russian roulette with a six-shooter.)

This idea of a global “carbon budget” emerged about a decade ago, as scientists began to calculate how much oil, coal and gas could still safely be burned. Since we’ve increased the Earth’s temperature by 0.8 degrees so far, we’re currently less than halfway to the target.

The 565-gigaton figure was derived from one of the most sophisticated computer-simulation models that have been built by climate scientists around the world over the past few decades.

The Third Number: 2,795 Gigatons

This number is the scariest of all – one that, for the first time, meshes the political and scientific dimensions of our dilemma. It was highlighted last summer by the Carbon Tracker Initiative, a team of London financial analysts and environmentalists who published a report in an effort to educate investors about the possible risks that climate change poses to their stock portfolios. The number describes the amount of carbon already contained in the proven coal and oil and gas reserves of the fossil-fuel companies, and the countries (think Venezuela or Kuwait) that act like fossil-fuel companies. In short, it’s the fossil fuel we’re currently planning to burn. And the key point is that this new number – 2,795 – is higher than 565. Five times higher.

Which is exactly why this new number, 2,795 gigatons, is such a big deal. Think of two degrees Celsius as the legal drinking limit – equivalent to the 0.08 blood-alcohol level below which you might get away with driving home. The 565 gigatons is how many drinks you could have and still stay below that limit – the six beers, say, you might consume in an evening. And the 2,795 gigatons? That’s the three 12-packs the fossil-fuel industry has on the table, already opened and ready to pour.

We have five times as much oil and coal and gas on the books as climate scientists think is safe to burn. We’d have to keep 80 percent of those reserves locked away underground to avoid that fate.

Yes, this coal and gas and oil is still technically in the soil. But it’s already economically aboveground – it’s figured into share prices, companies are borrowing money against it, nations are basing their budgets on the presumed returns from their patrimony. It explains why the big fossil-fuel companies have fought so hard to prevent the regulation of carbon dioxide – those reserves are their primary asset, the holding that gives their companies their value. It’s why they’ve worked so hard these past years to figure out how to unlock the oil in Canada’s tar sands, or how to drill miles beneath the sea, or how to frack the Appalachians.

You can have a healthy fossil-fuel balance sheet, or a relatively healthy planet – but now that we know the numbers, it looks like you can’t have both. Do the math: 2,795 is five times 565. That’s how the story ends.

Read the whole story by Bill McKibben in Rolling Stone