The carbon countdown

One of the recurring questions around climate change is the matter of how long we’ve got to stop it. What’s the timetable for emissions cuts? When do emissions need to peak? Or is it too late already?

These are questions that can’t be answered with a simple figure. Like the question of how many people the earth can support, it needs a few qualifiers. What do we mean by avoiding climate change? Given that a certain amount of warming is already locked in, it’s a matter of deciding how much is too much – 2 degrees is the usual consensus. Some argue it should 1.5 degrees, especially those small islands states that would be at very serious risk by the time we get to 2 degrees. Others say 2 degrees is too ambitious politically, and we should aim for a more realistic 3 degrees.

The other decision we need to make is how much risk we’re prepared to run. There are no definites, but are we looking for a good chance at preventing dangerous climate change? Or would we settle for a 50/50?

The IPCC’s latest carbon budgets gives us a range of options, that Carbon Brief have explained this week. The options can be mapped like this:

carboncountdown

Here are three different targets, 1.5, 2 and 3 degrees of warming, and three different risk profiles for each – a 33%, 50% or 66% chance of staying below that target.

You can then take the amount of CO2 that we can safely emit (the carbon budget) and divide it by current consumption. If you want a better than even chance of staying below 1.5 degrees, we’ve got just six years at current levels of CO2 emissions. In other words, that’s not going to happen.

That’s not six years before we need to act, in case the graph gives that impression. That’s the total budget at current rates. As we cut emissions, that time might extend. If emissions rise, and they are still rising, then that time is going to get shorter.

There is no satisfying answer to the question of how long we’ve got to bring down emissions. It’s a matter of odds. The longer we leave it to turn a corner and start driving down emissions, the faster the budget will be consumed and the greater the chances of runaway warming.

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