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What Happens If We Don’t Mitigate?

July 8, 2015 5:58 am2 comments

[This piece was slightly edited for brevity and readability; see full video of the session on YouTube.]

Quirke: Hello gentlemen. Thank you for your time today. Dr. John Nielsen-Gammon, I’ll start with you. If you wouldn’t mind, please tell us what’s in store – in terms of global rain distribution patterns and warming – if we fail to mitigate the emissions of greenhouse gases and what’s in our power to affect change on this issue.

Dr. Nielsen-Gammon: Well, we are kind of on autopilot for the next 30-40 years because it won’t be possible to change emissions very quickly or suddenly. Anything we do now is going to have a big impact on the second half of the 21st century. What we are seeing with temperatures is that, so far, they have gone up by almost a degree Celsius. The latest numbers are higher than any previous year’s, so I think the hiatus [in global surface temperature] is probably over.


In terms of future warming, projections are for another degree or so by mid-century—perhaps more, perhaps less. It’s hard to say exactly. Basically, there will be warming, over the long haul, everywhere on the globe.

As for rainfall, it is more of a mixed bag because air goes up in some places to make rain and then it descends in other places that are dry. So that you have some places that get more rain, and some places that get less. Probably, the rainfall amounts will increase because warmer atmosphere contains more water vapor. But then again, higher temperatures accelerate evaporation, so there are going to be impacts in terms of creating drought in some places also.

Quirke: In one of your posts, you mentioned that your best estimate for warming under a business as usual scenario—which I guess is unsuccessful mitigation and somewhere between the IPCC’s RCP 6.5 and 8.5 emissions scenarios—is 3°C by 2100. Does that best estimate still hold true?

Nielsen-Gammon: That is a reasonable ballpark estimate. Of course we don’t know exactly what “business as usual” means in terms of how much CO2 will be in the atmosphere by 2100. Best guess right now is something like 3 to 4 times the amount of CO2 in preindustrial times [(editor’s note: the preindustrial concentration was around 280 ppm, so Dr. Nielsen-Gammon’s estimate equates to around 840-1120 ppm)], which is well past doubling [(editor’s note: doubling is around 560 ppm)].  So the amount of warming that goes with that is probably around 3 degrees. It is hard to say exactly because we don’t know exactly how sensitive the climate system is to exchanges of inputs and outputs. Even if you know exactly what is going to happen in terms of the atmospheric composition, the temperature could come in as low as 2 degrees above preindustrial or as much as 5 degrees above pre industrial. It depends on which indicators of sensitivity turn out to be correct. We can look at past observations, they give us one set; we can look at paleoclimate, which gives us another set; and models give us a third set. There is overlap between them all, but they are not all converging at a point.

Quirke: Our readers have followed these three bases for estimated sensitivity—the observations, the paleoclimate data, and the models—and are tracking how, together, they point to a 2 to 5 degree Celsius range of warming. [Editor’s note: 5 degrees Celsius might not sound like much to some folks, but that is the approximate difference in global average temperature between the coldest period of an ice age and the hottest period of a warm period or “interglacial” in the Earth’s glacial history in the modern epoch.]  This estimated climate sensitivity, or ECS for short, is the warming response for about 100 to 150 years or so—after a doubling of atmospheric CO2 from the preindustrial amount of around 280 ppm (the peak for a warm period) to around 560 ppm. [(For more on the 2 to 5 degree Celsius for ECS, see Key Findings of the IPCC AR5 Synthesis Report (Official Slideshow).)]

Nielsen-Gammon: Also, in terms of expected warming by 2100, one should know that if you were to flatline emissions at 2100, the temperatures would still keep going up because it takes a long time for the oceans to come to equilibrium. The top layer might be at equilibrium, but the oceans are constantly replacing surface water from deep down. Furthermore, on committed warming: Even though warming is only 7/10ths of a degree so far, we are committed to almost 1.5 degrees Celsius due to how long it will take the oceans to catch up.

Quirke: So what is the ballpark number for ultimate warming, in terms of the ultimate response, compared to the preindustrial period? I guess this should include the most likely scenario and the tail-risk, “worse-case” scenario (the latter of which is important in any risk assessment).

Nielsen-Gammon: Well the farther you get into the future, the more the uncertainties pile up, and you start getting into Mauri’s territory [(glaciers)], because the ultimate temperature depends on how the ice caps are affected on Greenland and Antarctica. If some of that melts, it not only affects sea levels but also affects the albedo of the earth, which determines how much sunlight gets absorbed. And so that longer feedback might kick in depending on how rapidly the ice recedes. Overall we are probably talking on the order of 4 to 7 degrees [Celsius] perhaps, for a ball-park no-mitigation scenario. But then, when we are talking about the next century and the century after, who knows what technology we will have to actually be able to remove carbon dioxide and take other actions. It is really science fiction when you get too far out there.

Quirke: Yes, but that being said, with warming locked in for thirty or forty years, if we wait until it gets really bad to do something about climate change, that doesn’t seem like a recipe for success.

Nielsen-Gammon: Yeah that’s the problem, if you wait until the middle of this century, you are pretty much committed to the end of the century.

Quirke: And I concede that we are pondering the distant future in this burning-the-earth’s-carbon experiment. I can’t help but think of the famous quote by the legendary scientist, Admiral Roger Revelle, who once wrote: “Human beings are now carrying out a large scale geophysical experiment of a kind that could not have happened in the past nor be reproduced in the future.”

But back to the glaciers; you kind of touched on their long-term response, and you mentioned how that’s really important. This long-term response, which gets into the albedo effect, is this what you call “earth system sensitivity”?

Nielsen-Gammon: Yes.

Quirke: Dr. Bart Verheggen was saying (see previous link) how some scientists—Dr. James Hansen, former head of NASA Goddard Institute of Space Studies, among them—believe this could be twice as much as the ECS (or hundred-year response). Again, I know we are talking about uncertainties here, but we are making a decision by doing nothing. I am just trying to get a handle on how far and how much our policies this generation can affect the future.


NASA simulation of Arctic sea ice coverage based on satellite imagery. Source: NASA

NASA simulation of Arctic sea ice coverage based on satellite imagery. Source: NASA.

Nielsen-Gammon: You are absolutely right, and, yes, we could very well be talking about turning the climate into conditions that haven’t been present for tens of millions of years, ultimately. But that is one scenario that assumes we don’t figure out a way to solve the problem ever. I think that is unlikely.

But that brings us back to the problem of if you wait until the middle of this century, then you are pretty much committed to the end of the century. That is one of the difficulties of dealing with global warming, because the impacts that you are trying to avoid by doing something are not the impacts that you are experiencing now. They are the impacts that are possible or probable several decades down the road. It’s like saving for retirement. You don’t want to go broke when you are retired; granted, it’s hard to visualize that when you are 20 or 30 years old, but that’s when saving makes the biggest difference.

Quirke: I now want to Dr. Mauri Pelto. Dr. Pelto, feel free to add or respond to Dr. Nielsen-Gammon’s comments, but also please mention the current rates of sea level rise and the melting of glaciers, and, if you will, also talk about the second and third orders of effects of these things, in terms of societal response. I know that this is a very broad subject in environmental science, but you are probably more used to these kinds of questions from your students. I mean, the question of what kind of changes will we have to adapt to—the answer to that lies not just in physics. It concerns the policies of nations and states and how we deal with one another. It’s a harder question.

Pelto: I would just go back to what John [Nielsen-Gammon] was saying—talking about what would happen at 4 degree warming. I would go back to what we were talking about as glaciologists back in the 1990s and 1980s. I remember a conference in Vancouver, and our real focus then was on what we thought to be the weakest link in Antarctica. We thought that it would be a good analog to do the same in Greenland, so some campaigns were mounted back in the 1980s to observe those glaciers, and now we are taking advantage of some longer range data sets in other areas. So when we did that, did we expect in 2003 to see what’s happening to this magnitude? I don’t know. What I do know is that all this [glacier loss] is taking place with only about one degree warming; not even quite one degree warming.

Also, the alpine glaciers—on the first Earth Day—back in 1971; the Alpine glaciers were doing pretty well around the world. You went to the Alps or the North Cascades or the Canadian Rockies, and the alpine glaciers were robust and healthy… You look at today and you look at 31 straight years that we have lost volume. It is not a good business model to lose mass every year.

Quirke: Am I correct that, in terms of the melting glaciers, that change is occurring faster than what most scientists—the majority of scientists—originally predicted?

Pelto: When you talk about Greenland and Antarctica, that is definitely true. I am not sure it is true about the alpine glaciers, but with Greenland, I don’t think we expected to see in the mid-90s that all 200 glaciers would start to accelerate by 2010.

[Audio problems]

With four degrees, we can’t see much hope for the Greenland ice sheet. And that would be a large contribution to sea level rise around the world.

Quirke: Could you speak on the wider implications of this? If we fail to mitigate successfully?

Pelto: In terms of sea level rise, what you see is not only the atmospheric temperature that is causing problems for many of the glaciers and ice sheets, but also it’s ocean temperature. Of course, there is a different heat capacity for the ocean; [the warming oceans] are demonstrating an excellent ability to melt the base of these outward glaciers, even if they are not that exposed to the ocean.

Quirke: And as mentioned by Dr. Schmittner, there really hasn’t been a hiatus at all in the ocean heat content. Now that we are speaking of the oceans, I’m going to hand it over to Dr. Will Howard. Dr. Howard, feel free to add more on sea level rise or on anything else that we’ve covered, but please tell us about ocean acidification. I would be remiss if we skipped that issue.

Howard: I just want to make a couple comments on what both Dr. Nielsen-Gammon and Dr. Pelto said. Dr. Nielsen-Gammon was talking about changes in precipitation patterns. We can already see some of that predicted behavior: dryer parts getting dryer, wetter parts getting wetter. You can see it in ocean salinity. One of the innovations we have is the Argo floats. These are autonomous instruments that float around and measure temperature and salinity, and they come back up and transmit their data. And one of the patterns we can see is that places where evaporation exceeds precipitation, they are getting saltier; and the slightly fresher parts of the ocean are getting fresher. This is just the pattern that you’d expect from what Dr. Nielsen-Gammon was talking about. So, this isn’t a prediction anymore, this is actually being seen in the data.

I also want to comment quickly on something Mauri Pelto said. There has been a combined oceanographic and a glaciological study down in one of the ice shelves, and you can already see now the thinning of the ice shelves on [inadudible] Glacier, largely due to the effect of the ocean underneath it. In fact, you might say in Antarctica that the ice shelves are all that are holding back the flow of the glaciers, from accelerating their flow, into the ocean. So he has a very good point about the ice shelves and how little we actually know about what is happening within them and underneath them. That is really new science that has just come out in the last few months. So that is an area we are looking at.

Also, just real quick on the ocean: We can almost account for the climate heat budget; we can almost say where the extra heat locked in by greenhouse gasses has gone; 90% of the heat is within the ocean. Again, you can already see that, there is no hiatus in ocean heat content. It is continually going up and up and up.

Quirke: And regarding the much-talked about “hiatus,” I just want to keep this in context. When we are talking about climate in general, we are talking about long range trends; and based on my experience as a journalist covering this issue, climate scientists don’t get too excited about short, decadal changes because it gets noisy at that scale. But has any particular new stuff come out on that, in terms of the ocean heat and this accounting for the energy budget?

Howard: Nothing new particularly lately [as of this taping on 4.24.2015], it’s just a set of findings that are building up and keep reinforcing one another. I should also point out that the other piece that we are getting closer to closing is the sea level budget. And part of the sea level rise, approximately 3mm a year, that you can see from the altimeters: part is driven by the melting of glaciers, but a lot of it is driven by the thermal expansion of the ocean as it warms. And that has been a challenge to close that budget, but I think we are getting closer in understanding that quite a bit of it is driven by the thermosteric component of sea level rise. Sea water expands as it warms. So that is an area where a lot of progress is being made. Part of that is because we have better instrumentation. Things like the satellites that effectively weigh ice sheets from space—so you have a better estimates of what is the mass balance of Greenland or Antarctica. So we are starting to get closer to closing those kinds of budgets.

Nielsen-Gammon: I just wanted to clarify something, some people [reading] this might not know what “closing the budget” means.

Howard: Oh, right. No problem. So, we can see sea levels going up, and the problem is, of course, that that’s just about the only thing you can measure accurately. We can measure the rise, but we don’t know where it is coming from. It is not easy to measure the mass of an ice sheet and know exactly where it is losing and gaining mass. They are slightly gaining in the interior of Antarctica we think. But when we say closing, we are just trying to figure out where all the sea level rise is coming from. Some of it is coming from melting ice, some is coming from the ocean itself as it is warming up and expanding. So it has been a challenge figuring out what is actually providing that known sea level change. And part of it is having good observations in the ice sheets and the deepest parts of the ocean.

Quirke: Dr. Pelto, you wanted to add something?

Pelto: It has been interesting to see how things have developed. We do have the satellites that can take a measure of the ice sheets. We also have altimeters. And we are getting the same answer from both. We didn’t have either one of those instruments 15 years ago, so now it is pretty easy to quantify. But looking back, we also can create from some of our maps in the past, not a good timeline, but a single time when we knew the volume, and we could see for example that Greenland and Antarctica weren’t contributing as much to sea level rise in the 1990s… We can quantify [glacial volume] pretty well now, but it only comes up to half or just a tad over half of the sea level rise we are observing, and the other half is coming from the oceans themselves.

Quirke: Dr. Howard, I was hoping you would be able to talk on ocean acidification as well.

Howard: Oh yes, sorry, I was just interested in the other contributions. The first thing about ocean acidification is that it doesn’t arise from the radiative behavior of greenhouse gases. So our understanding of ocean acidification is completely independent and separate from debates on equilibrium climate sensitivity; it’s not dependent on issues like cloud feedbacks or vapor feedbacks. This is behavior arising from the chemistry of one of the greenhouse gases—carbon dioxide (rather than, say, methane). It arises from CO2 dissolving into sea water and forming a weak acid—carbonic acid. And this chemistry, though not simple, is pretty well known. It’s not unlike the chemistry in your bloodstream. When you breathe, you breath out CO2—you get rid of it—and therefore maintain your blood pH. In fact, physiologically, your blood pH cannot change more than a 10th of pH units. And the ocean has already changed by a bit over a 10th, so that should put things into perspective.

So ocean acidification is a consequence of the ocean taking up the atmospheric emissions we are producing. At the moment, the ocean takes up about a quarter of all the emissions we produce in a given year, based on best estimates. And we know about a half of our emissions accumulate in the atmosphere and cause warming, about a quarter is absorbed by the oceans, and the other quarter by the land.

What it is doing is shifting the chemistry of the ocean away from carbonate ions and toward bicarbonate ions, and that is a function of the ocean trying to maintain its own pH balance. And again, it is becoming less alkaline, if you prefer, and becoming more acidic. And the pH scale is not a linear one. So even though it’s only changed about a little over .1 pH  unit, that is about a 30% change in ocean acidity.

Quirke: And the consequences of this?

Howard: So the consequences are that we have already seen a shift away from conditions that favor shell-forming organisms: coral and coral reefs, a whole range of planktonic organisms that are building shells in calcium-carbonate (the same material that you find in sea shells). And that consequence is that… well, we don’t know the consequences that well. One of the obvious consequences is that reef-building organisms, tropical reefs, are already slowing their rate of growth; so corals have already slowed their calcificiation rates. This is extremely important if you think about small island atolls. Those islands are there because as the volcanic corals have subsided, the sea level has gone up (since the last ice age), and the growth of coral organisms has kept up. Now we are facing an interesting situation. Now are we not only raising sea level, at the same time we are comprimsing the ability of these systems to grow fast enough to keep up. It’s not just that organisms are growing slower, but geolocially, it is also that these reef systems have been maintained by a mass balance between the growth of organisms and rate their dead skeletons dissolve. This net rate of dissolution; that’s an area that it is not easy to get observations on and we are only starting to understand—that is, the importance of that net accretion. Some folks here in Australia have just completed a thirty year studying showing how net accretion has gone down. That is an important implication for folks that live in, say, the Marshall Islands.

Quirke: And coral reefs, aren’t they the rainforests of the ocean? Correct me if I am wrong, but isn’t there not a lot of life between these bio-diverse, clusters of life?

Howard: Yes, the biodiversity of these coral reefs—these are hot spots; and I think the interesting issue is that, the more we look at the biological response of these organisms, the more complex their responses seem to be. For me, physics, chemistry, and geology are simple, but biology is hard. The responses of these organisms vary.

What I look at, is that on this ship of an ecosystem, the winners and losers will begin to manifest themselves, and that is something that we are just starting to understand. Compare that to say, the chemistry of carbon dioxide in water—the latter has been known for decades, a century really. But the biological responses are really the problem. There are organisms that are resilient, some even benefit, so it is not all bad for every organism. But what that means for how the ecosystem will change—that goes to the core question [audible issues] that people’s livelihood depends on.

And just one more thing: I am a geologist and paleo-oceanographer by background, so I have spent most of my life studying long-term carbonate dissolution cycle in the ocean, and one of the key things we understand is that the timescales that the ocean will buffer the CO2 going into it are extremely long – I am talking like a millennia. So when we put a big dose of CO2 in the atmosphere, much of it will absorb into the ocean.

Ultimately, the ocean has plenty of capacity—in terms of sedimentary carbonate on the bottom of the ocean—to buffer all that CO2. That is the good news. The bad news is that it is going to take thousands, if not tens of thousands, of years for all that buffering to take place. What happens before the buffering is complete is what we have to worry about.

So, earlier we were talking about committed warming; there’s an analogous problem of committed acidification.

Quirke: It’s just longer.

Howard: Much longer. Orders of magnitude longer. And another problem is the CO2 is being absorbed at the top, and the ultimate buffering capacity is at the bottom. The analog would be that you have an upset stomach, and you took a Tumbs, but it takes 5,000 years for you to feel better.

Quirke: A 5,000 year stomach ache.

Howard: Yes. That is another point—in terms of commitment—that people need to understand if we don’t mitigate. It is not like other pollution problems that we can turn around quickly.

Quirke: A superfund pales in comparison. It is mind-boggling, as someone coming at this fresh, to think of these time scales, in terms of impacts. So ok, there’s a lot locked in the pipeline. So what can we affect—and this is a question for all three scientists—by a mitigation scenario akin to the IPCC’s RCP 2.5 or RCP 4? What change can we affect in this generation—in the next few decades?

Nielsen-Gammon: One aspect of the answer is that a lot of things seem to scale with the temperature: the impacts are larger with larger temperature change. So you can’t say, well, if you cut the warming down by half, we’ll cut down the change by half. The problem with change is not change per se, but the consequences of change. And the consequences of change tend to grow exponentially with the magnitude of change. So if you reduce the change by half, you may reduce the mangitidue of impacts by a factor of 10 or something like that. That is how much our world and society is structured to a nice, narrow range of temperature we have developed with.

The other problem concerns the category of tipping points. That is, if you get to change beyond a certain magnitude, things start happening that you didn’t expect to see happening. We are already seeing the unexpected, but they haven’t had significant and immediate consequences yet. So if you cut back on emissions—thereby reducing the magnitude of change—you’ve reduced the likelihood that something seriously bad will go wrong that you wouldn’t expect to happen. So it is insurance against that possibility.

Quirke: And that brings up the “tail risk” in a basic risk assessment—based on what is known and unknown [see Tail Risk vs. Alarmism].

Anything else on tipping points or tail risk from Drs. Pelto or Howard?

Howard: It is interesting for me, given the timescales of my usual perspective, to hear about tipping points, because that is truly an area of deep uncertainty. This is an emerging area of science. People are just now sort of getting an idea. I am often asked, how will we know if we are at a tipping point? We’ve seen tipping points before. The collapse of Carribean reefs was a tipping point (it was due to a lot of things, not just climate change), but that was a tipping point we didn’t see coming. It’s just hard to spot tipping points beforehand. From my perspective, I would say we are actually in someways past some tipping point, in terms of the issue of the carbonate issue of the ocean. Or, if not past the tipping point, then past a point where a recovery transition will take so long that it might as well be a tipping point. That is something people don’t understand.

Pelto: From the standpoint of glaciers, we are not too worried about individual glaciers. In terms of tipping points [regarding glacial volume on a global scale], it is hard to grow a glacier back. It is easier to maintain a glacier. So you set a pretty strong barrier to getting a glacier back once you melt it. With ice caps, it’s worse. [Audio cut out.] You are not going to be able to rebuild those. So in some cases, we’ve passed the tipping point. [Certain glaciers and ice caps] still exist, but we are past the tipping point.

Quirke: Thank you for your time gentlemen. I hope to hear more about these implications in the Forum; and as we move into the policy discussion, I ask for your help in keeping the policy debate moored to the science. Gracious thanks.


  • I’m a bit confused by John’s statements in the paragraph starting “That is a reasonable ballpark estimate…”

    Assuming an [atm. CO2] in 2015 of 400 ppm, a continuation of the recent rate of increase (about 0.4% per year, to 962 ppm in yr 2100), and the IPCC AR5 median ECS, then:

    y2100.co2 = 400(1 + (1.004^85)) = 962ppm
    y2100.dRF = 5.35ln(y2100.co2/280) = 6.6 W/m^2
    doubling.dRF = 5.35*ln(2) = 3.7 W/m^2
    y2100.dT = 2.9(y2100.dRF/doubling.dRF) = 5.16 deg. C

    And that’s considering only the feedbacks inherent in the ECS definition, that is, the “fast feedbacks” and those from the oceans; no invocation of ESS feedbacks (e.g. carbon cycle or ice sheets), which would increase the estimated dT still further.

  • … where 2.9 = median AR5 ECS from GCM models

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  • Jim Bouldin

    I’m a bit confused by John’s statements in the paragraph starting “That is a reasonable ballpark estimate…”

    Assuming an [atm. CO2] in 2015 of 400 ppm, a continuation of the recent rate of increase (about 0.4% per year, to 962 ppm in yr 2100), and the IPCC AR5 median ECS, then:

    y2100.co2 = 400(1 + (1.004^85)) = 962ppm
    y2100.dRF = 5.35ln(y2100.co2/280) = 6.6 W/m^2
    doubling.dRF = 5.35*ln(2) = 3.7 W/m^2
    y2100.dT = 2.9(y2100.dRF/doubling.dRF) = 5.16 deg. C

    And that’s considering only the feedbacks inherent in the ECS definition, that is, the “fast feedbacks” and those from the oceans; no invocation of ESS feedbacks (e.g. carbon cycle or ice sheets), which would increase the estimated dT still further.

  • Jim Bouldin

    … where 2.9 = median AR5 ECS from GCM models