Think Out Loud

New study quantifies climate feedback loops

By Sage Van Wing (OPB)
Feb. 28, 2023 10:12 p.m. Updated: March 10, 2023 12:33 a.m.

Broadcast: Wednesday, Mar. 1

When sea ice melts, it can lead to faster warming because water absorbs more heat than ice does. That’s one of more than 25 climate feedback loops found in a recent study from Oregon State University. Some of these feedback loops aren’t included in current climate models, partly because science, and the climate, are changing so quickly. Jillian Gregg, co-author of the new report, joins us to explain what we should understand about feedback loops.


This transcript was created by a computer and edited by a volunteer.

Dave Miller: From the Gert Boyle Studio at OPB, this is Think Out Loud. I’m Dave Miller. When sea ice melts it can lead to faster global temperature rise because water absorbs more heat than ice does. That’s one of more than 25 climate change amplifying feedback loops found in a recent study from Oregon State University. But some of these feedback loops are not included in current climate models, partly because the science and the climate are changing so quickly. Jillian Gregg is a co-author of the new report, she is a member of the faculty in the sustainability program at OSU, and a principal investigator for Terrestrial Ecosystem Research Associates. She joins us now to explain her findings. Welcome to the show.

Jillian Gregg: Thanks for inviting me.

Miller: So I mentioned melting sea ice there since it’s probably the most familiar feedback loop to a lot of our listeners, it was to me. But there are more than two dozen other ones that amplify climate change that you and your team have identified, and you divide them into different categories. Can you give us another example or two of a physical feedback loop?

Gregg: Another example would be evaporation of water into the warmer air. So as the air gets warmer, we get more evaporation of water into the air, and water is a strong greenhouse gas, so that helps to warm the planet. This is well known, included in all climate models.

Miller: I’m so used to hearing about CO2 and methane as heat trapping gasses, but water as well is another way that heat is trapped?

Gregg: Yes, so water is actually the strongest greenhouse gas, but we have no way to control it. It simply follows air temperature. The air temperature gets warmer then more water evaporates into the air. And as the air gets colder then you have more condensation and that water is rained out of the air. And that all happens within around a nine day cycle, so there’s no way that humans have to control or alter atmospheric moisture.

Miller: And that comes either from oceans or lakes or from soil?

Gregg: Yeah, anywhere it gets warmer, you can have more evaporation, you’re gonna get more moisture in the atmosphere. It’s not highlighted because it’s not a greenhouse gas that humans have control over, it’s just a natural process that is part of a physical feedback loop that is in all climate models.

Miller: And we don’t control it. We can control much of the other gasses or fossil fuels we’re burning that contribute to overall warming, but we don’t control the H20 itself.

What about another physical feedback loop?

Gregg: Another physical feedback loop would be CO2. CO2 naturally dissolves into the ocean waters, and actually that causes acidification which is harmful for ocean life. But as the oceans get warmer, the oceans hold less CO2. And that’s a physical thing, the same as if you open up a soda and then someone calls, you gotta go do something, if you were to put that soda in the fridge, then when you come back later there’s gonna be more CO2 or carbonation in your soda. But if you leave it out in the hot sun that will have all dissipated out into the atmosphere. The same thing happens with the ocean, as the globe gets warmer, more of the CO2 is released into the atmosphere. And that is another physical factor that needs to be accounted for in all climate models.

Miller: So these are physical ones involving kind of pure chemistry, but you also have found some biological feedback loops. What are some examples?

Gregg: It’s not that we found them there, they are well documented. We did a literature review, and our point is there’s so many of them that we need to get a handle on all of them. But a couple more well documented ones are wildfire feedback loops. As the forests burn, there’s the heat of the fire, but that is minor compared to the amount of CO2 that’s emitted to the atmosphere. So all of the carbon from all of the trees and wood that burns then goes into the atmosphere and stays there for hundreds of years, absorbing the heat that’s trying to leave the earth and re-radiating it back to earth in the greenhouse effect. So the warming of the planet causes more drought, more drought can cause more fires, and more fires causes more burning, and more burning causes more CO2 in the atmosphere, which ultimately causes warmer temperatures. So it’s a cycle.

Miller: I should note there’s actually a third category that’s included in the totaling up of these feedback loops which are called human feedback loops. Just for some examples in the paper, political upheaval could lead to less international cooperation, or an increase in conflict because of dwindling resources tied to climate change could lead to an increase in emissions from military action.

What’s the connection between the kinds of feedback loops that you’ve been talking about and so-called climate tipping points?


Gregg: There are a number of planetary tipping points. Tipping points are like, say you’re taking a kayak down a river and there’s the current of the river, but you could always turn around and if you’re strong enough, go upstream and get back to where you started from. But at the point when the river goes over a waterfall, you’re not going to be able to get back up the waterfall.

The same thing happens in the climate system, where it’s thought that there are tipping points where we have admitted so many greenhouse gasses that these feedback loops can continue in and of themselves without us contributing further greenhouse gasses. We could at that point get to net zero emissions, and the climate is continuing on the self perpetuating feedback loops. And so that could accelerate us towards these tipping points where we’re not able to get back to our original state.

Miller: And what are the ones that seem most serious or, to go back to your metaphor, the falls that we seem closest to arriving at right now?

Gregg: Two very close ones are the Amazon rainforest and the melting of Greenland. So with the Amazon rainforest, in 2021 there were more emissions of CO2 from slash and burn agriculture than the forest took up themselves. So at one level, rather than the whole Amazon forest, which is supposed to be helping to take the CO2 out of the atmosphere and store it and ecosystems, even just last year it was emitting more carbon than it was absorbing. But the long term concern with Amazon or other forests is forests actually help create the rain. And so if we cut down the forest so much that they are not transpiring the water into the atmosphere to provide the rain that they need to grow, we could cross a tipping point where we are not actually even able to regrow the forests.

And with Greenland, it is thought that melting could get so fast that all of the ice on Greenland can melt, and that would lead to a rise in sea level of approximately 20ft.

Miller: We’ve been focusing on the ones that fall into the majority of the ones that you found, these are the ones that amplify climate change. But there is a smaller number of what I guess I would call beneficial loops that do the opposite. So what’s an example of a feedback loop that could actually mitigate climate change?

Gregg: As I just described, photosynthesis is the primary beneficial feedback loop that we have. Photosynthesis is the reaction that plants use to take CO2 out of the air to create sugar. It’s natural, it’s already here, and we need to make sure to protect as many ecosystems, land and ocean, as possible to maintain this function.

Miller: There’s also a third category in the paper where it seems that there’s just too many question marks to know at this point how the feedback loop might play out what’s actually going on. What’s an example where more research is needed?

Gregg: Well, clouds are a really good example of that, although there is quite a bit of research into clouds. But there’s quite a big difference if it’s high wispy clouds or low lying thick clouds. And in the future as it gets warmer, certainly there’ll be more moisture in the atmosphere, therefore we could have more clouds. And whether those clouds are going to be high and wispy or low and thick, various clouds can help to trap more heat in the system and other ones can help to reflect more of the sunlight from coming in. And so clouds would be an example of a feedback loop that’s more uncertain, that we need to know more about.

Miller: I should let listeners know that there’s a really great climate feedback loops project website, part of this OSU project that your team put together, with a full round rundown of all the loops we’re talking about and many more, along with some interactive ways for people to actually see how these loops work too to increase warming and decrease sea ice and see that the cycles moving in different ways. I recommend folks check it out, we’ll put a link to that loops project website on our website.

Gregg: A quick point about that website is that we don’t see our list as static there. We have this extensive literature review, we sent it out to over 20 experts, but we expect more loops to be found in the future, and maybe more more references that we could cite. And so we welcome people to go to that website to comment on, add to, and interact with this list.

Miller: So check it early and often.

How many of the feedback loops that you’ve identified are already in climate models?

Gregg: Various models are gonna have different amounts of them. But if you look at the IPCC AR6 report, in their tables they cover at least half of the ones that we have identified on these lists, so they’re definitely being considered. Our concern is just that we came up with 27 amplifying loops, and certainly all of those amplifying loops are not currently in models. We think models are excellent and ever evolving, and so we know that’s really the next generation, the next step is to look at what is going to be the effect if you include all of the feedback loops. We put a call out in the paper, we think it would be fantastic if the IPCC could do a special report where they quantify the relative watts per meter squared per unit area of the planet to look at the relative impact of the different feedback loops and include them in models. And maybe when you include them all, it doesn’t make temperatures rise even faster than we’re already expecting. But we just are concerned about them, and want to make sure that they’re looked at in detail.

Miller: In your mind, if you use this lens of these feedback loops, especially the amplifying feedback loops, does this research suggest new interventions or mitigation strategies? Or is it just one more reminder, as if we needed one, that we’ve got to get our act together as a species and reduce emissions?

Gregg: It is a reminder. We’re a bit concerned that we have until 2050 to reach net zero emissions. Right now the worst case scenario models are considering the worst case of emissions. And so that’s great because we need to know the worst case. But we’re thinking worst case is not only worst case emissions, but also worst case of the feedbacks on the climate system. So we may not have yet reached the worst case scenario models, and if you’re gonna get a car and you want to crash test, you want to know the [possibilities]. You want to know the best case, but you also want to know the worst case so that we can plan accordingly. And it might be that we need to get to net zero emissions far before 2050.

Miller: Jillian Gregg, thanks so much for joining us.

Gregg: Thank you.

Miller: Jillian Gregg is on the faculty of the sustainability program at Oregon State University and is a principal investigator for Terrestrial Ecosystem Research Associates

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