Shift Key Classic: The World Will Miss 1.5C. What Comes Next?

Shift Key is off this week for Memorial Day, so we’re re-running one of our favorite episodes from the past. With Republicans in the White House and Congress now halfway to effectively repealing the Inflation Reduction Act, the United States’ signature climate law, we thought now might be a good moment to remind ourselves why emissions reductions matter in the first place.

To that end, we’re resurfacing our chat from November with Kate Marvel, an associate research scientist at Columbia University and the NASA Goddard Institute for Space Studies. At the time, Trump had just been reelected to the presidency, casting a pall over the annual United Nations climate conference, which was then occurring in Azerbaijan. Soon after, he fulfilled his promise to pull the U.S. out of the Paris Agreement, with its goal of restraining global warming to 1.5 degrees Celsius over pre-industrial levels.

In this episode, we talk with Kate about why every 10th of a degree matters in the fight against climate change, the difference between tipping points and destabilizing feedback loops, and how to think about climate change in a disappointing time. Shift Key is hosted by Robinson Meyer, the founding executive editor of Heatmap, and Jesse Jenkins, a professor of energy systems engineering at Princeton University.

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Here is an excerpt from our conversation:

Robinson Meyer: I want to dive into tipping points for a second. Are there particular tipping points that are really frightening to you? Because sometimes it feels like that phrase gets used for almost two different things: There are some tipping points where once we start them … these are physical effects in the climate system that once we start, we won’t be able to really reverse them, and I think the Atlantic Meridional Overturning [Circulation] is the classic example, and we should probably explain what that is.

But then there are other tipping points, sometimes, where it’s like once you start them, they don’t only have this cascading physical effect that’s irreversible, but they have a cascading effect on the carbon cycle.

Kate Marvel: Yeah, no, I mean, they all freak me out quite a lot for different reasons. Your point that we use, at least colloquially, tipping points to refer to a lot of bad stuff deserves a little bit more attention — I personally see tipping points getting confused with feedback loops and runaway greenhouse effect.

So, a feedback process is when global warming affects things that exist on the globe, which themselves feed back onto that global warming. So a classic example of a feedback process is ice melt. Ice is super shiny. It’s very reflective. It turns back sunlight that would otherwise fall on the planet and warm it. And we know — you know, science is very solid on this — that when it gets hot, ice melts.

Jesse Jenkins: That’s a good one. Yeah, we’re clear on that.

Marvel: So when ice melts, you take something that used to be shiny and reflective, and now you’ve got darker ocean or darker ground underneath, and so you’re no longer turning back that sunlight. It’s getting absorbed, and that itself feeds back to the warming. That makes the warming worse. So that is an example of what scientists call — and this is the worst terminology in all of science — we call it a ‘positive feedback.’ Because when normal people hear positive feedback, they’re like, Oh, I’m doing a great job. But when scientists say ‘positive feedback,’ we mean ‘destabilizing process that is making warming worse and might lead to catastrophe.’ So I’ll try to say destabilizing feedback and stabilizing feedback, but catch me out on it if I say positive and negative.

So there are a lot of these feedback processes that we understand pretty well. We know that warmer air holds more water vapor — that’s why we’re seeing more intense, extreme downpours. And we know that water vapor is itself a greenhouse gas. So when the planet gets warmer, you’ve got more water vapor in the atmosphere, which itself is trapping more of the heat coming up from the planet. That is an example of a destabilizing feedback.

So there’s a lot of these feedback processes that we understand fairly well. And then there’s some processes that we are not completely baffled by, but we haven’t really nailed down as much. So that’s why clouds are a huge wild card. A lot of the reason we don’t know exactly how hot it’s going to get is we don’t know what clouds are going to do. We don’t know how clouds are going to reorganize themselves. We don’t know if we’re going to get more of this one type of cloud, less of this other type, if they’re going to get more reflective, more absorbent, whatever. Clouds are really complicated, and that’s a feedback process that we don’t necessarily understand.

But feedback processes are already happening in the climate system right now. They are going on as we speak. That makes them different from something like a tipping point. A tipping point is generally defined as something that we break that we can’t fix on any timescale that’s relevant to us. So an example of a tipping point is the disintegration of the West Antarctic Ice Sheet. It turns out that once you break an ice sheet, it’s relatively really hard to make a new one. We can’t just rock up in Antarctica with, you know, freezer guns or whatever Arnold Schwarzenegger had in the Batman movie. We can’t do that. That’s not real. Once we break the West Antarctic Ice Sheet, it’s going to be broken for the rest of our lives, and our children’s lives, and our grandchildren’s lives.

Music for Shift Key is by Adam Kromelow.