Why We Have Eleven Years

I'm not going to have time to get my usual grueling Twitter round-up posted by the end of today, May 1, because life is intruding, so I hope to get it together tomorrow. (Please contain your disappointment, as I will mine.)

Instead, I have one thread of tweets from Brad Plumer, who covers climate for the New York Times. He is speaking into a conversation that happened on Twitter yesterday among what seemed to be all of the U.S.-based climate journalists and thinkers I follow, responding to a new report I barely saw go by the day before, but which had even more bad news on the acceleration of carbon accumulation in the Earth's atmosphere.

To put it most simply, these writers and thinkers had divergent thoughts on whether 2030 or 2050 should be the goal for the U.S. to reach carbon neutrality if the world is to stay at no more than 1.5°C of warming.

Here's what Brad had to say about it:

I think it's fair to say the U.S. probably has to hit net zero emissions by somewhere around 2030 for the world to stay below 1.5°C of global warming. (Whether that's feasible or not is a different question.)

It's true the IPCC doesn't specify this. They just say that the world *as a whole* probably needs to get to net zero by somewhere around 2050 to limit to 1.5°C with little overshoot. And the world would need to hit net zero by ~2070 to stay below 2°C.

(There are all sorts of ways to fiddle with these dates — by, for instance, assuming massive and perhaps unrealistic amounts of carbon removal later in the century. But let's stick with this base case.)

The IPCC says nothing about individual countries. But I think this paper by Glen Peters
is fairly clarifying on this question. He looks at staying below 2°C, not 1.5°C, but the intuition is similar in both cases. (link in the original)

Basically, the world *could* stay below 2°C if emissions in the U.S./Europe decline steadily to near-zero by 2050. But in that scenario, China/India would have to make even more aggressive reductions, and the rest of the world could basically emit nothing.

There's a reasonable argument that this isn't really fair. That the U.S. and Europe should act even more aggressively (say, getting to zero by 2030 or so) to give poorer nations more space to develop. That's not a scientific mandate—it's a question of ethics and politics.

One could counter, of course, that this is technically impossible—that the U.S. can't and won't get to net zero by 2030. Possibly true! But then you either have to argue that other countries have to make even *more* radical cuts, or that we're very unlikely to stay below 1.5°C.

Anyway, I've seen a bunch of people say it's not *necessary* for the U.S. to zero out emissions by 2030, that there's no scientific mandate to do so. And that's totally true, there's not! But it's at least worth being clear on what follows from that.

I found that useful in the midst of all the other confusion and debate. As Shaun Chamberlain says,

It is now impossible to be realistic about both the political climate and the physics of climate. One must decide which carries more weight and be profoundly unrealistic about the other.