Interview with Gavin Schmidt

This is a re-post from Carbon Brief by Roz Pidcock

Schmidt has been the director of NASA’s Goddard Institute for Space Studies since June, 2014. He is the principal investigator for the GISS ModelE Earth system model. In 2014, he gave a TED Talk on the “emergent patterns of climate change”, which has been viewed more than one million times online. He was one of the founding scientists of RealClimate.

CB: We’ll kick off with something topical. So NASA has just announced that Arctic sea ice has reached its annual minimum, and is the fourth lowest on record. What is the significance of this, do you think? And how does it fit in with what we know about global ice cover?

GS: So, the thing to remember is that the ice in the Arctic is undergoing a long-term decline, and while there are ups and downs in any one particular year, the main thing to be looking at is the trend, and the trend has been solidly one of decline for the last 30 or 40 years, and that’s very, very significant. The loss of extent is something like 10% per decade, for the minimum. That’s really very large, and they’re already seeing huge impacts from that change in climatology in the Arctic – in terms of the biology, the ecosystems, people living there, erosion… Everything is being affected in the Arctic by this, and this year’s change is exactly on trend.

CB: Is there any good news at all with Arctic sea-ice? There was a NASA study that suggested that, perhaps, older, multi-year sea ice was recovering a bit since the 2012 low. Is that happening?

GS: So, what you are seeing is, again, some of that inter-annual variability that is driven by, you know, the vagaries of the weather in any particular summer season. It’s not in any sense a recovery, but, obviously, once you have a really exceptional year – the one you had in 2012 – anything after that is going to look like it’s a recovery, but the long-term trends are very, very dramatic. The sea-ice thickness has gone down by over 40%, the amount of old ice – so this is the thick, ridged ice that’s been around for multiple seasons – has gone down to historic lows. So, it’s not going down to the extent where it’s all going to disappear this year or next year, but the decline is very significant and is steady.

CB: Antarctic sea-ice has shown some quite unusual behaviour this year, tracking quite high for the first half and now dropping below average. Is that El Niño, or is there something else going on there?

GS: So, there is an El Niño response in Arctic sea ice. We’ve set up a kind of dipole pattern upon either side of the Antarctic peninsula, and we’re already seeing a weird pattern there because of the way that the ozone hole and the winds associated with the changes in the ozone have projected on to the sea ice as well. I think the key in the Antarctic is that there’s a lot of internal variability that we don’t have a great handle on. I mean if you look at the simulations of Antarctic sea ice they’re not very good. And so our ability to attribute changes in the sea-ice component of Antarctica is actually quite poor. So we’ve seen, you know, years that have been quite high, years that have been again below average, but the overall trends are much smaller and less significant than the ones in the Arctic. And, actually, that is predicted. It is predicted that the northern hemisphere and the northern pole region is going to respond faster than the south, basically, because there’s more land in the Arctic higher latitudes than there is in the Antarctic.

CB: So, what is NASA doing to keep track of how ice cover is changing and what are perhaps some of the challenges that you face?

GS: So, all of these records come from satellites – microwave soundings – so the microwaves allow you to see through the clouds, to see what’s underneath. They’re not perfect, so you have to work a little bit to make sure you’re looking at exactly the same thing every year. But NASA is continuing that series. There’s a whole series of satellites that’s been going since 1978, and that series will continue. Our ability to monitor that is really a function of NASA’s investment in earth orbiting satellites.

CB: Your own research background includes palaeoclimate. So, what lessons about our future climate can we learn by looking into Earth’s past? And, perhaps more importantly, are we learning those lessons?

GS: I think there’s still a lot of work to be done, which is why it’s interesting scientifically. But what we can do is we can go back in time and, while there isn’t something that’s a perfect analogue for where we’re going to be, there’s been lots of examples of where the climate has changed for all sorts of reasons – the changes in the orbit of the Earth, big volcanoes, the main ice age cycles themselves – and that gives us an ability to test our understanding in these kind of new circumstances. And if we can get that right – if we can understand what was going on then – we can have more credibility in projecting out into the future. For instance, in the early Holocene – so that’s about 6,000-8,000 years ago – the orbit of the Earth was such that northern hemisphere summers were actually warmer than they are today, and that had impacts on Arctic sea ice that we can pull out of the palaeo record. And we can also test our models in those circumstances: what happens in the models to Arctic sea ice when you change the orbit like that. And what we found, actually, is that the models that respond more appropriately – and quite significantly – in that early Holocene period are also the ones that have an earlier reduction of sea ice going into the future. So, that kind of gives us some indication that the models that get the past right are predicting a slightly faster decline in sea ice going into the future.

CB: So what inspired you to take the route that you did through climate science? And who or what continues to inspire you now?

GS: I started off as a mathematician and the only thing I cared about was doing interesting math problems. And that kind of led to Oxford, where I did a maths degree, and I didn’t really know what to do with that afterwards, so I kind of bummed around for a while. Then when I came back from that I was looking for more of a challenge, and I just went to the maths department at University College London and said: “Oh, maybe I could do a PhD?”, and they said: “Woah! No, you can’t just come in here, walk in and expect to do a PhD – there’s a process, there’s applications – it’s all been decided months ago!” So, I was like: “Oh, I’m terribly sorry.” And then they said: “Well, you might want to go and talk to that guy over there.” So, I went to talk to that guy over there, and it turns out he’d just had something funded and he was looking for graduate students and he said, basically: “Oh, when can you start?!” So, I said, “Oh, in a couple of weeks.” So, I just walked into that. And he turned out to be working on problems associated with ocean circulation, and as I got into more applied mathematics – problems that have a real-world connection – what I found was that people were more interested. You could talk about these things and you could actually do things that people cared about. And as I’ve gone from theoretical oceanography to simple models of the climate and now to much more complex models of the climate, what I find is that I’m able to answer and explore questions that more and more people care about. And so that’s really what drives me. Instead of just imagining a spherical cow and making some great theory about that, can you make things as realistic as possible? And, actually, have a real connection to the phenomena and the patterns of change you see in the real world?

CB: What do you think are the biggest unknowns about future climate change? Where are the biggest surprises likely to come from?

GS: I think the first thing to acknowledge is that there will be surprises. We’re moving into a regime of climate that we have not experienced as humans, most ecosystems have not experienced since the beginning of the ice age cycle some three million years ago. We don’t know very well what exactly was happening then. We know some big things, like how much the sea level rose and what the temperatures were like, but there’s a lot of things that we don’t know. And so we are anticipating “unknown unknowns”. But, of course, they’re unknown, so you don’t know what they’re going to be. So, things where we don’t have a really solid basis – exactly what’s going to happen to clouds, exactly what’s going to happen to some of the extreme events that have the biggest impression on society and ecosystems – and we’re pushing things in a way that all of those systems are going to be affected – some will be affected more than we expect and some less – but I don’t know which!

CB: Related to that uncertainty is the difficulty in pinning down climate sensitivity, and that has attracted a lot of interest in some sections of the media. Do you think how high or low it is has any implications for policy, or is it largely a scientific question?

GS: It’s very, very, very likely not to be so low that we don’t need a policy response, and it’s very, very unlikely to be so high that any policy response is pointless. So, we’re kind of in that middle point where any of the real scientific uncertainty doesn’t actually have that much implication for policy. The difference between 2.5C for a doubling of carbon dioxide and 4C for a doubling of carbon dioxide; you still have impacts by the end of the century that are worth, in my opinion, mitigating against either way. Of course, the higher the sensitivity is, the faster that’s going to come, but given the way the inertia in the system works, that’s making a difference of a decade here or there. So it’s not really that important in policy, given that the policy measures that we’re putting into place have to be sustainable for multiple decades.

CB: So, your personal view, or from your own research, what do you think is the likely value of climate sensitivity? Where do you put it?

GS: I think it’s between about 2.5 and 3C. We’ve got some work that we’ve been looking at trying to reconcile different estimates that come from different kinds of experiments or different kinds of observations. And one of the things that we’ve found is that in some of the calculations where they come up with a slightly lower number there are some systematic problems with those kind of calculations that mean that that’s not really a valid response and it really should be little bit higher, in line with the estimates that have comes from paleoclimate, which I think are the more robust ones.

CB: So, in terms of getting a handle on the impacts we can expect, what do you think the integrated assessment models that try to model the economic impact of climate change and then try to compare that with the cost of mitigation or the cost of doing nothing, do you think that’s useful?

GS: Do you want me to be polite or do you want me to be honest?

CB: Honest opinion, always.

GS: So, I’ll try and be polite and honest. I think that in concept they’re fine, but I think their ability to actually make sensible estimates of economic costs is hopeless. You know all of their things are kind of global, sector-level estimates. The damage function is a function of temperature to some power, maybe squared. And that’s not how things are going to work. Different sectors are going to be affected by different things. There’s a lot of thresholds where a small change in temperature is not going to change anything very much, but once you get past some threshold, you’re going to start to see a lot of changes. You’re going to start to see impacts because of sea-level rise that are not directly tied to the temperature at that exact point. So my feeling is that we yet do not have an appropriate fit-for-purpose set of economic models that can really do this problem. And a lot of the things that people have put together – and the estimates that even appeared in the last IPCC report – are really not fit for this purpose. I mean they are useful in some ways. You know you can explore how economics and climate can fit together a little bit. But in terms of making a real useful and policy-relevant forecast for what the damages are going to be, we’re not there yet. And I know that there are some efforts, you know at the University of Chicago, and elsewhere, to make the GCM [General Circulation Model] for economics that is required. But they’re not yet mainstream, and they’re not yet at the point where we can have a lot of confidence in those results. So, all of those estimates of damages, I think they might be lucky, they might be right, but there’s not a real basis to suppose that they are correct.

CB: So, what do you think is the most underfunded topic in climate research, or what is your biggest frustration about current climate research? Or, maybe put it another way: what questions would you like to see answered more than any others?

GS: So let’s break that down a little bit. I mean there’s a lot of stuff that’s being done in climate adaptation, climate mitigation, that isn’t the kind of research that I’m interested in. Well, I mean I’m interested, but it’s not the kind of research that I’m involved in. If I stick to the research, the science of the climate system, I think what we really need to be investing in is real data centres that allow you to sift through all of the model data, all of the observations in really intelligent ways that would allow us to probe the information that we have already, that comes out of the satellites, that comes out of the weather models, that comes out of the GCMs, far more efficiently than we are able to do right now. I mean you may be aware we had a project called CMIP which was a coupled model intercomparison project, where all the groups that did models of the Earth’s system did a certain set of experiments for the future, for the past. That dataset is above five petabytes of data, which is enormous. And our ability to sift through that and pull out interesting metrics, to look and see how different processes are being simulated in the models and in the weather models and actually observed by the satellites, is very, very limited. So, I think we really need a very large investment in that kind of cyber-infrastructure to allow us to do better and more intelligent science on this. You know I work for NASA so I’m supposed to say that we need more investment in new satellite technology, and there are a couple of instruments that we’ve tried getting into space on multiple occasions, and we haven’t yet succeeded. One of which is an aerosol polarimeter, which would really give us for the first time a description of where in the atmosphere there are these aerosol particles, and what kind of particles they are. That’s kind of the biggest unknown in terms of the atmospheric composition, and all of those things have impacts on radiation, they have impacts on atmospheric chemistry, they have impacts on ozone and smog, and so those are really key measurements to be making, and, hopefully, we’ll be able to do that again soon.

CB: So, when is NASA going to call 2015’s temperature? Is it going to be the hottest on record?

GS: That’s something that our lab puts together, and we do the end of year summary in January, and we’ll wait until January. I mean the indications are that 2015 will be a record year. I did a quick calculation a couple of days ago based on the January-August amount, the anomaly that we have so far. It looks like it’s got about a 90% chance of being the hottest year on record, given the past relationship between the year and that particular period. It doesn’t look like it’s going to cool down any time soon. You know we’ve got this continuing El Niño in the Pacific and very warm North Pacific temperatures, so those are going to be continuing to have an effect. So, I think it is likely – not quite very likely – that 2015 will be a record year. But as we get towards the end of the year it will become more or less obvious. I will update that calculation as we go through the year.

CB: And what do you think about when people say 2015 being the hottest year on record, and indeed 2014, what do you think about when people say that signals the end of the so-called slowdown in surface warming?

GS: So…this so-called “slowdown”…it’s really not clear that that ever existed. I think you have to think a little bit in terms of the different timescales. If you think about the longest timescales, you know multiple decades, there’s no evidence for a change in the underlying trend. If you look at shorter timescales then, yeah, there’s timescales when it’s going down, timescales when it’s going up, and there’s variation because of things like El Niño, because of things like the Pacific Decadal Oscillation. It’s not at all obvious that what we saw from the peak El Niño in ’97, ’98 to the really deep La Niña in 2011, you know whether you can explain almost all of that with just understanding what ENSO does, understanding what the short-term forcings have been doing – things like volcanoes, things like the solar variations, things like variations in the amount of aerosols coming from China versus the US. And I don’t think that there’s really anything left there to be explained. There’s nothing really anomalous there. So, what you’re seeing here – 2014 was a classic example – if you go back to 1997 and said, “OK, well, if I just take the Niña trend and I make a prediction for what 2014 would be”, you’d have got it exactly right. So, you know the evidence that there was a change in trend in the meantime is very slim. And now 2014 was a record year, 2015 as we said was likely to be a record year, given the persistence of ENSO, also carries over into the following year 2016 is likely to be very warm year as well. So what you’re seeing is basically just a clearer acknowledgement that the underlying trend really hadn’t changed that entire time.

CB: So, is it fair to say, then, that whether or not there’s a “hiatus”, whether or not people think there is one, it depends quite a lot on the definition?

GS: Well, people have been very loose about what they’ve defined it as, and so, if you’re interested in short-term trends, then you can attribute those, you can dive in and say, why was one year warmer than the other, why were these five years cooler than those five years? Those are totally valid questions to be asking. But then the question that it kind of gets morphed into is then, well, what does that mean for the future, what does that mean for the long-term trends. And that connection has often been kind-of implicit, rather than explicit, and I actually don’t think there’s very much connection at all.

CB: Do you think it was a problem then that the IPCC in its last report gave quite a focus on the hiatus, and even used the term “hiatus”, when before that it existed in the media really. Do you think the IPCC was right then to do what they did in the last report?

GS: So, I think the IPCC might have been better off just talking about the difference between short-term trends and long-term trends, and how the different attribution works for those. The problem with the IPCC trying to keep up with a kind of moving story is that they’re constrained to only be looking at the literature that came out before the report came in. But if you actually look at where the explosion of papers was it was actually after the IPCC report was finished. So I think now we have a much better idea about what’s going on. But they kind of got ahead of the publication process. It’s not that there was anything wrong in what they wrote, but, in terms of focus, and in terms of utility of their contribution, it wasn’t very useful.

CB: Just in the last few weeks there’s been quite a lot of media coverage, at least in the UK, talking about natural variability and the impact that it has on long-term trends. So, there’s talk of Pacific decadal cycles, Atlantic decadal cycles and El Niño. Do you think that we’d be in a better situation in terms of media and public understanding of global temperature if we’d been having all of these conversations a long time ago?

GS: Scientists have been having those conversations the entire time. What the UK media decides is interesting on any one week is completely random. So if you ask people in six months’ time what they remember about any of this discussion, I think that would be an interesting study. Go back in six months’ time and ask people what they remember about any of these discussions, and we’ll see how much it’s penetrated. People have been talking about internal variability since before climate change was a thing, and we’ve always said these two things are happening in concert. Often people choose to focus on worst case scenarios – even if you give them a range, it’s the highest number that makes the headline. That’s more of a problem in the dailies than it is obviously for Carbon Brief or for any of the more specialised sites. But that lack of context and that incomplete ‘soundbitisation’ of science results is not going to go away any time soon, and it isn’t anything that the scientists can force the media to fix – though the scientists and other parts of the media, particularly foundation-supported stuff, can provide important context for people so that people don’t make too many decisions based on a headline in the Daily Mail.

CB: So, talking of the IPCC, who would you like to see as the new chair – to succeed [Rajendra] Pachauri? And is it important, do you think, whoever gets the position?

GS: So, oddly enough, lots of people keep asking me this question! I haven’t really been part of the IPCC. I’ve never been on the lead author committees, and I’ve only ever had a very peripheral role, so I’m not actually sure what it takes to be the chair and who the best person for that is. So I’m going to stay studiously neutral on that one.

CB: Well, Carbon Brief has a series of interviews with all the candidates, so you could have a read of those! [laughs]

GS: I will, and I’ll do my research and call you back! [laughs]

CB: Well, the IPCC more generally then. People might see a new chairperson as a new era for the IPCC – a chance to revamp or re-energise. How do you think the IPCC can make sure it evolves with the times, to stay relevant? Or do you think that isn’t a problem?

GS: The problem with the IPCC process is the tasks that they set themselves, which every seven years is to write basically an encyclopaedia of climate change. Up to the minute. That’s an enormous burden on the whole community, not just the people writing for the IPCC. It sets up weird incentives to have certain publications come in before weird deadlines that really don’t make any sense. I don’t think that that is sustainable. The science doesn’t change so much on a five-to-seven year basis that you have to redo the encyclopaedia every single time. I would be supportive of an IPCC that set aside this idea of being totally comprehensive and instead focussed on directed questions that came from the member governments. So, instead of scientists getting together and coming up with a list of all the things that we think are important and that other people should pay attention to, I’d much rather that the IPCC was directed towards specific questions that the policymakers want answered. So if they want to know, “how do we combine controls on short-lived pollutants and long-lived pollutants in a coherent framework?”, then let’s have an IPCC special report just on that. And I think that would be very interesting. If policymakers wanted a special report, “what should we be planning in terms of sea level rise?”, then let’s have a special report just on that. I don’t think we need to go into every single piece of detail of climate science every single time, because things do get updated. There are things that are done better over time, but those are not things that are necessarily policy-relevant. The difference between the AR4 [Fourth Assessment Report] palaeo-history of carbon dioxide figure and the AR5 [Fifth Assessment Report] palaeo-history of carbon dioxide figure – there’s clear improvements in the science between one and the other – but none of it is policy-relevant, except in the very grossest sense. So, if IPCC kept to a more defined, policy-relevant set of questions, then I think the burden on the community would be lessened and the product would be more applicable and appropriate.

CB: So, something that was policy-relevant in the last IPCC report was the concept of carbon budgets. How effective do you think that is for policymakers? Do you see the message getting through?

GS: There are two elements of the carbon budget discussion that have been used a lot. I think one of them is very, very useful, which is this notion that carbon dioxide accumulates in the system and the impacts that we’re going to see are a function of the total amount of stuff you’ve put in the atmosphere. That’s very different to how other pollutants work that are more short-lived – whether it’s smog, or ozone, or sulphates, or anything like that. And that’s a very important concept for policymakers to embed in their thinking, because that does make a difference to how you’re going to plan for various trajectories. It makes a difference to whether you’re going to have a peak early or later and how that all works out. The one part of it that I see talked about in some places, that I don’t like so much, is this idea that there’s a fixed budget that, therefore, we have to avoid exceeding – like one trillion tonnes – at all costs. That’s not valid because what that’s confusing is an element of, “what’s the marginal extra damage any particular emission is going to cost over time?”, with an arbitrary target, and usually this target is the two-degree warming target. It’s not worth paying an infinite amount of money to avoid crossing that target because the damages between 1.9 and 2.1 degrees are going to be higher, but there isn’t a cliff at two degrees. It’s not like we actually have a budget and then we have to spend it and then as we get down it becomes more and more expensive to share out the remaining credits. Some people talk like that – particularly Kevin Anderson – they talk about what you’re going to do to avoid breaking that budget, and I don’t think that that language is particularly useful, and I don’t think that concept is very helpful to making sensible decisions.

CB: You mentioned two degrees there. Do you think that two degrees is still a feasible target to aim for – whether it ends up being 2.1C, 2.2C – do you think two degrees is still valid?

GS: Ken Caldeira makes this point. What’s the target for the number of little old ladies you want to have mugged every year? The target is zero, right? Because obviously that’s not something you want to do. So are you going to make it to the point where you’ve got to zero? No. But it’s still useful to have a target, because if you set a target of “we only want a hundred old ladies to be mugged”, that would be horribly unethical. So I think setting targets as low as can be conceived of I think is sensible – whether you actually achieve them or not. Two degrees is not totally out of the question, though I think it is not likely that we will make it. But any of the decisions that we’re making now, to get us on a path towards reducing emissions, they’re the same decisions we’d be making if the target was 3C, or 2C, or 1.5C. The actual actions that people need to make are the same. So discussion of the target – quite frankly – I think is mostly a waste of time.

CB: Virtually all the pathways available to us for two degrees – as outlined in the IPCC report – do rely to some extent on BECCS (bioenergy with carbon capture and storage), and that technology doesn’t exist yet on a large scale…

GS: Well, it’s not just BECCS, but any kind of carbon capture, or negative emissions, or sucking carbon out of the atmosphere. But, yes, all the RCP2.6 scenarios do rely on that to some extent, and I think that that really underlines the challenge that we have going forward. I think people should be investing in how to do that on a scale level, but, obviously, it’s not going to happen unless there’s a significant carbon price, which, obviously, as you know, does not yet exist.

CB: So, given how ambitious it is to stay below 2C, is 1.5C off the table?

GS: In terms of a realistic target? I think that that is very very unlikely.

CB: Is there a role for scientists to play in the run-up to the Paris negotiations later this year? Or is the job of scientists done?

GS: The job of a scientist like me is mostly done. People are talking about their independent contributions to reducing emissions, countries are talking about this and they’re talking about many different ways that they’re going to get there. That means that those countries are taking this problem seriously, and that really has been the contribution that the climate scientists who have focussed on the physical system, like me and my group and the other groups like them, have been looking at: things like attribution of changes in the past, forecasts of changes in the future given whatever scenarios. People have taken that to heart, right? Nobody is arguing about whether carbon dioxide is still a greenhouse gas – outside of the fringe blogs. These are serious commitments, even from countries which have a vested interest in continuing fossil fuel extraction. So, to a large extent, our job is done. But this goes back to the previous question: it’s not inconceivable that the governments involved, both in COP and the IPCC, would have specific questions that they would like us to answer, that we’re not getting the message on. We’ve done a lot, for instance, of policy-specific scenarios. So, you have a baseline and then you say, “What happens if we do this policy? What would happen? What would be the consequence in terms of climate, in terms of air pollution, in terms of ecosystem health, in terms of public health?” – we’ve done a lot of those kinds of simulations, and that isn’t really part of the IPCC, but we find that the policymakers that we’ve done that for find those things very, very useful. So, are there other questions that the member governments of both COP and IPCC want answered that are within the physical science realm? Then we can answer them, and we can make sure we get a good robust response to that. We spend a lot of time worrying about what climate feedbacks are. We spend a lot of time worrying about the interaction of radiative change and circulation change.

All of those things are fascinating and interesting, but none of those are really going to change what people decide to do, right? 

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