At the Copenhagen climate talks in 2009, the countries of the world agreed to a target: they would strive to limit global average temperature rise to no more than 2 degrees Celsius above preindustrial levels. It was a bold and stirring declaration of purpose.

Oddly, global carbon emissions just kept rising, like they had for decades. What to do?

The answer, clearly, was an even bolder and more stirring declaration of purpose. That’s what we got in Paris, where countries agreed that 2 degrees is fine and all, but the real target should be 1.5 degrees.

Thus far, that hasn’t worked either — global carbon emissions are still rising.

Before they go and lower the target again to yet bolder and even more stirring levels, let us pause for a moment and contemplate that 1.5 degree target. Researchers Jan Christoph Minx and Sabine Fuss (Minx & Fuss!) have a great piece in Huffington Post that takes it seriously and examines what would be required to reach it.

Long story short: we already spent our "carbon budget." All the carbon necessary to drive temperatures to 1.5 degrees has already been emitted, or will be in the next five years or so. So from now on, if we want to limit temperatures to that level, we have to remove a ton of carbon from the atmosphere for every ton we emit.

That’s what this chart shows:

As you can see, hitting either target will require an almost immediate reversal of the trajectory of carbon emissions, from rapidly rising to rapidly falling. Overnight, pretty much.

And hitting either target will require descending beneath 0 carbon emissions, i.e., removing more carbon from the atmosphere than we emit.

The difference is, hitting 1.5 degrees will require re-absorbing 10 to 25 years worth of carbon emissions, which amounts to several hundred gigatons, using technologies — carbon sequestration, biochar, reforestation — that are, in their current state, horrendously expensive, woefully inadequate, or both.

And that is why we are probably fucked. Happy Thursday!

Further reading