That difficult "12 years to act" issue

Myles Allen tries to clarify what climate activists should be saying, rather than some of the sloppy sloganeering they are currently using: 

My biggest concern is with the much-touted line that “the Intergovernmental Panel on Climate Change says we have 12 years” before triggering an irreversible slide into climate chaos. Slogan writers are vague on whether they mean climate chaos will happen after 12 years or if we have 12 years to avert it. But both are misleading. 

Using the World Meteorological Organization’s definition of global average surface temperature, and the late 19^th century to represent preindustrial levels (yes, all these definitions matter), we just passed 1 degree Celsius and are warming at more than 0.2 degrees C per decade, which would take us to 1.5 degrees C around 2040. 

As the relevant lead author of the IPCC’s “Special Report on Global Warming of 1.5°C,” I spent several days last October, literally under a spotlight, explaining to delegates of the world’s governments what we could and could not say about how close we are to that level of warming.

That said, these are only best estimates. We might already be at 1.2 degrees C and warming at 0.25 degrees C per decade—well within the range of uncertainty. That would indeed get us to 1.5 degrees C by 2030: 12 years from 2018. But an additional quarter of a degree of warming, more or less what has happened since the 1990s, is not going to feel like Armageddon to the vast majority of today’s striking teenagers (the striving taxpayers of 2030). And what will they think then? 

I say the majority, because there will be unfortunate exceptions. One of the most insidious myths about climate change is the pretense that we are all in it together. People ask me whether I’m kept awake at night by the prospect of 5 degrees of warming. I don’t think we’ll make it to 5 degrees. I’m far more worried about geopolitical breakdown as the injustices of climate change emerge as we steam from 2 to 3 degrees. 

So please stop saying something globally bad is going to happen in 2030. Bad stuff is already happening and every half-degree of warming matters, but the IPCC does not draw a “planetary boundary” at 1.5 degrees C, beyond which lie climate dragons. 

What about the other interpretation of the IPCC’s 12 years: that we have 12 years to act? What our report said was, in scenarios with a 1 in 2 to 2 in 3 chance of keeping global warming below 1.5 degrees C, emissions are reduced to around half their present level by 2030. That doesn’t mean we have 12 years to act: It means we have to act now, and even if we do, success is not guaranteed.

And if we don’t halve emissions by 2030, will we have lost the battle and just have to hunker down and survive? Of course not. The IPCC is clear that, even reducing emissions as fast as possible, we can barely keep temperatures below 1.5 degrees C. So every year that goes by in which we aren’t reducing emissions is another 40 billion tons of CO₂ that we are expecting today’s teenagers to clean back out of the atmosphere in order to preserve warm water corals or Arctic ice.