zero emissions

There’s a recent paper on carbon cycle uncertainties and the Paris agreement (Holden et al. 2018). It considers two mitigation pathways, one that keeps end of century warming to below ~2oC, and the other that keeps end of century warming to below ~1.5oC. The interesting thing about the paper is that it uses a climate-carbon-cycle model (i.e., it considers emissions, rather than concentrations) and it also considers scenarios that don’t include negative emissions. The reason I wanted to highlight the paper is that it says something that I think is worth repeating.

A widely held misconception is that given the approximately 1 °C warming to date, and considering the committed warming (warming that will inevitably happen) concealed by ocean thermal inertia, the 1.5 °C target of the Paris Agreement is already impossible. However, it is cumulative emissions that define peak warming. When carbon emissions cease, terrestrial and marine sinks are projected to draw down atmospheric carbon dioxide (CO2), approximately cancelling the lagging warming. Although the sign of this ‘zero emissions commitment’ is uncertain, its contribution can be neglected for low-CO2 scenarios. Therefore, at least when considering CO2 emissions in isolation, keeping below 1.5 °C of warming will remain physically achievable until the point that it is reached.

Essentially, it’s never actually impossible to keep warming below some level, until we’ve actually crossed that threshold. Of course, it’s not going to be possible – in reality – to immediately get emissions to zero, but I do think it’s worth recognising that our warming committment depends largely on how much we emit in future, and that the ocean thermal inertia does not mean that there is warming that we cannot avoid.

A couple of other interesting results in the paper. One was that the carbon cycle uncertainties contribute quite a lot to the peak warming uncertainty. The other is that in these rapid decarbonisation scenarios, decadal variability can dominate over the mean response in some critical regions. Something that I should probably make clear, though, is that even though it is never technically too late to avoid further warming, even this paper indicates that having a good chance of limiting warming to levels below about 2oC (relative to 1870) without negative emissions will require emitting no more – since 2017 – than about 300-400 gigatonnes of carbon. That’s about 30-40 years at current emissions. It might be possible, but it’s not going to be easy.

There is some criticism in the comments because I said “30-40 years at current emissions”. For clarity, I wasn’t suggesting that we simply carry on as we are for 30-40 years, and then instantaneously stop. I was simply trying to put the carbon budget into some kind of context. To limit warming to ~2oC is going to require (without negative emissions) that we emit from now (in total) no more than what we would emit were we to continue emitting at current levels for about 30-40 years. To do this will almost certainly require steep emission reductions starting very soon.


A bit more about committed warming (a post with some more details about our committed warming).
Emission reductions, negative emissions, and overshoots (a post about emission pathways that would satisfy the Paris goals).

Posted in Climate change, Policy | Tagged , , , | 104 Comments

Rethinking climate policy

Roger Pielke Jr has been promoting his new paper in Issues in Science and Technology. The paper is called opening up the climate policy envelope and Roger has been suggesting that people should read it. I’ve read it a couple of times and there are some things I agree with, and some things that seem somewhat confused. The overall suggestion, however, seems reasonable (consider a broader range of policy options) but – unless I’m missing something – I’m not really seeing anything specific, or anything particularly insightful.

The paper criticises the use of BECCS and negative emission technologies in many of the scenarios. I think this is a perfectly fair criticism. We haven’t even really developed these technologies yet and have no real idea if they could be implemented at scale. There’s a section about how the rate at which we’re currently decarbonising is well below what would be needed if we wished to achieve some of the targets. Again, seems quite correct. Then there’s the obligatory complaints about the use of RCP8.5, which we discussed in this this post, and a dig at Kerry Emanuel. I think he misses the mark here, and one should bear in mind that Kerry Emanuel was the one who wrote a response to Roger’s 538 article.

So, some of the criticisms seem quite valid. However, one of the things I found a bit confused was the claim that

[t]he restricted policy envelope that results from the scenarios of the IPCC — typically formalized in the form of so-called integrated assessment models — is the result of two reinforcing sets of assumptions. One is that the costs of inaction will be high due to projected large changes in climate resulting from a massive increase in future emissions and resulting negative impacts on societies. The second is that necessary incremental actions to reduce and ultimately eliminate emissions will be technologically feasible at low cost, or even at no net cost at all—that such actions are economic and political no-brainers.

This doesn’t seem quite right to me, but then I’m not an expert at integrated assessment models. I thought some of these results at least emerged from integrated assessement models, rather than them being assumptions.

Another thing that seemed confused was that

[a]t the center of the current approach is a target and a timetable. The target is to stabilize concentrations of carbon dioxide in the atmosphere at a low level. In the past this level was commonly expressed as 450 parts per million carbon dioxide equivalents, and more recently has been expressed as a temperature target such as 2 degrees Celsius (2°C).

Well, stablising temperatures is not really the same as stabilising concentrations. The common target is to stabilise temperatures by getting net emissions to ~ zero. If you want to know more about this, see this comment.

The paper ends with a set of suggestions as to how we could expand the policy envelope. The responses to some of these seem quite obvious. If we didn’t include BECCS in the scenarios, then it would seem much more difficult to get net emissions to ~zero. If we abandon the 2oC target, then we’d probably make it even more certain that we’d miss this target. If we focussed less on worst case scenarios, then everything would seem more positive. However, I think it is well worth considering how we expand carbon-free energy, how we substantilly reduce our use of fossil fuels, and how we scale up new technologies.

A couple of things did surprise me about the article. There was no real discussion of how those who dispute the need for climate policy influence our ability to implement it. We’re not developing climate policy in some kind of vacuum. It’s not as if all we need to do is find the optimal policy and it will be implemented; there are many who dispute the need to do so. In some sense, there’s a whiff of deficit model thinking. Also, I didn’t see any mention of a carbon tax, which I had thought was one of the preferred policy instruments. I think the idea of us trying to expand our policy options is well worth considering. It’s just not clear in what way this article helps us to do so. Maybe I’m missing something, though, so if others have seen things that I’ve missed, feel free to point them out.

Posted in advocacy, Carbon tax, IPCC, Policy, Roger Pielke Jr | Tagged , , , , | 290 Comments

Climate misinformers

There’s been a rather lengthy debate on Twitter about Skeptical Science’s Climate Misinformers page. The discussion involved, amongst others, Richard Betts, Peter Jacobs, Steven Mosher, Gavin Cawley, and – briefly – myself. Before I start, I should acknowledge an association with Skeptical Science and should mention that I have published some papers with people associated with Skeptical Science. I also think it’s mostly an excellent resource and that it is quite remarkable what has been achieved, without any funding, by a group of, mostly, amateurs.

I do, however, have some sympathy with the criticism. The list does appear to label the individual, rather than labelling the behaviour. Some of the entries don’t have much in the way of evidence. Some of those included (Richard Muller, for example) have ultimately changed their views and have since made a positive contribution (Berkeley Earth). The list also only includes people whose misinformation aids arguments against climate action; it doesn’t include any who exaggerate in order to promote stronger climate action. It also has the potential to make the site appear political, which can make it – in some circumstances – difficult to use as a resource.

However, few of the criticisms involve arguing that some of those included do not deserve to be on the list (in the sense that there is no reasonable argument one could make for inclusion). In my experience, those included either do it intentionally, don’t do it intentionally but should know better, or regularly say things that are then highlighted by those who oppose climate action. This is essentially why I find it hard to get too bothered about Skeptical Science having a Climate Misinformers page; all of those included seem deserving of such a characterisation. Would it be better if Skeptical Science had focussed on the science and left this kind of thing to deSmogBlog? Maybe, but that ship has essentially sailed.

They could simply delete their Climate Misinformers page, but many who use this to criticise Skeptical Science, would probably then simply find something else to criticise. I also think there is some value in knowing about those who are associated with promoting misinformation. We should applaud any who recognise their errors and change their views, but I don’t think we should necessarily forget their less positive contributions.

What about it being political? I suspect those associated with Skeptical Science do have a bias. Like me, they probably think we should be doing more about climate change, rather than less. Being aware of this can itself be useful. One should also bear in mind that trying to remain politically neutral can also be criticised. This is a very complex communication environment and, in my experience, it is extremely difficult to engage in a way that satisifies everyone and that can’t be criticised by some.

Whatever one thinks of their Climate Misinformer page, Skeptical Science provides some extremely useful resources on their site and they’ve done a remarkably good job of carefully representing our scientific understanding. Given that it’s an almost entirely volunteer effort, I find this quite impressive. Others are welcome to disagree.

Posted in Climate change, ClimateBall, Pseudoscience, Uncategorized | Tagged , , , | 204 Comments

S S Sagaing

I’m on the train back from a meeting in Leicester, so have a bit of free time to write a post. I thought I might write about something a bit different to my normal posts. My father contacted me a few days ago to highlight that the Sri Lankan navy have just raised the wreck of a ship sunk during World War II. The ship was the S S Sagaing and it sank on the 9th of April 1942 while at anchor in Trincomalee harbour after being bombed by the Japanese.

The S S Sagaing burning in Trincomalee harbour, Sri Lanka, after being bombed by the Japanese; 9 April 1942. (Credit: Captain K. I. Macleod)

The reason for my interest is that my grandfather, Kenneth Macleod, was the second mate at the time. After abandoning ship, a suitcase floated past their lifeboat. After recovering it they discovered a camera and took the photographs on the right, showing the ship burning in the background.

This wasn’t the first time that my grandfather was on a ship that sank. He was also the third mate on the Kemmendine which was sunk by the German auxiliary cruiser Atlantis on the 13th of July 1940. The passengers and crew were picked up by the Atlantis and then transferred to other ships. My grandfather ended up on a Yugoslavian ship called the Durmitor which grounded near Mogadishu, Somalia.

The prisoners ended up in an Italian prisoner of war camp just south of Mogadishu. They were liberated in February 1941 by South African soldiers. The Royal Navy then asked them to crew some captured merhant ships back to the United Kingdom. I believe that my grandfather was one who did so, although he may have crewed one from Durban, rather than from Somalia (I shall have to check with my Mother). Less than a year later he’d signed on to the S S Sagaing, which a couple of months later was bombed and sank in Trincomalee harbour.

I think I managed to find the wreck on Google Maps. As mentioned in some of the reports, it was moved after being bombed and then sunk again to be used as a pier. If you compare the Google maps image with the image on the bottom left (from this article) you can see the red roofs of the buildings and also what look like some naval ships that are also in the lower corner of the Google maps satellite image. I’ve also included a larger satellite image showing where it is in Trincamolee harbour (or, used to be).

Posted in Personal | Tagged , , , , , , | 15 Comments

No, Hansen wasn’t wrong!

It’s 30 years since James Hansen testified before the US Congress about climate change. In the same year, he published a paper that produced some forecasts. I wasn’t going to write about this as there are a number of articles discussing what Hansen presented and highlighting how it’s stood up remarkably well. There’s Eric Holthaus in Grist, Gavin Schmidt at Realclimate, Zeke Hausfather at Carbon Brief, and Tamino at Open Mind.
Patrick Michaels and Ryan Maue have also written an article looking at how Hansen’s global warming predictions have stood up. They conclude that they haven’t stood up very well. Drawing this conclusions, however, requires making some rather odd claims. For example

Global surface temperature has not increased significantly since 2000, discounting the larger-than-usual El Niño of 2015-16.

Well, if you leave out some data you can draw all sorts of conclusions. However, why was the 2015/2016 El Niño warmer than the 1997/1998 El Niño? Why are La Niñ’a’s today warmer than El Niño’s of the past? It’s because there’s an underlying warming trend and, as the figure on the right shows, there is little indication that the rate of warming has slowed.

In Hansen’s paper, he selected 3 different emissions scenarios, one in which emissions continued to increase (A), one in which the rate stayed similar to what it was in the 1980s (B), and one in which they basically stop in 2000 (C). The Michaels and Maue article implies that temperatures have followed the latter scenario, while emissions have continued to rise. However, not only is this claim about temperatures wrong, what’s more relevant is the change in forcing, what turns out to have been between scenario B (constant rate of emission) and C (emissions stop in 2000). The resulting temperature change turns out to, therefore, be quite similar to what has been observed (see here).

The article finishes with

On the 30th anniversary of Mr. Hansen’s galvanizing testimony, it’s time to acknowledge that the rapid warming he predicted isn’t happening. Climate researchers and policy makers should adopt the more modest forecasts that are consistent with observed temperatures.

That would be a lukewarm policy, consistent with a lukewarming planet.

Firstly, it is not true that forecasts are not consistent with observations (see here). Secondly, what is lukewarm policy? Seems to me that if you accept that climate sensitivity lies somewhere within the standard likely range, think we should limit warming to something reasonable (say, below 4K), and think we should do so without shocking the global economy, then it’s not clear to me that there is much difference to the basics of what you would want policy to achieve. We would need to aim to get emissions to ~zero by the second half of this century. We could quibble about the details, but the basic goal would seem to not depend strongly on where you think climate sensitivity actually lies.

Both Michaels and Maue are associated with the Cato Institute, which seems to essentially be the US version of the UK’s Global Warming Policy Foundation, so I probably shouldn’t be surprised that they can write such a nonsensical article.


Credit: Zeke Hausfather

I wanted to add this figure that was produced by Zeke Hausfather, as it really illustrates the key point. The warming per unit change in forcing predicted by Hansen et al. (1988) is very close to what we’ve actually experienced.

James Hansen’s legacy: Scientists reflect on climate change in 1988, 2018, and 2048 (Eric Holthaus in Grist).
30 years after Hansen’s testimony (Gavin Schmidt at Realclimate).
Analysis: How well have climate models projected global warming (Zeke Hausfather at Carbon Brief).
Global warming: Told you so (Tamino).
Update check on Hansen’s 1988 projections (Nick Stokes at Moyhu).

Posted in Climate change, Climate sensitivity, ClimateBall, Policy | Tagged , , , , , , , , | 213 Comments

Planetary thinking

I was wanting to write a brief post about a recent Adam Frank article in the New York times called Earth Will Survive. We May Not. I also have a post about an earlier Adam Frank article, and I also listened to a podcast with Adam Frank and Joe Rogan, which somewhat influence my understanding of his recent article, and which I will post at the end of this.

The basic argument seems to be that life has always influenced the climate of the Earth, and that even though some of these changes have been quite cataclysmic, the biosphere has always endured and, ultimately, thrived. Therefore, the biosphere will almost certainly survive anything we might do.

My understanding, based partly on listening to the podcast with Joe Rogan, is that one of the ideas is to try and frame this whole topic slightly differently to how it is often framed. If life has always changed the climate, sometimes substantially, the idea that we have developed our advanced civilisation without doing so is bizarre. Additionally, the possibility that our activities can’t produce a substantial changes is similarly bizarre.

If we’re not careful, though, the biosphere might survive our impacts, but we (our civilisations, at least) might not. We can’t stop ourselves having any kind of impact, but we can think of ways to optimise our impact, so that we can continue to thrive.

In some sense, this argument makes sense, and since many other framings have been ineffective, maybe it’s worth promoting this basic idea. I do, however, have some concerns, and I’m interested in what others think. One concern would be the possibility that this gets interpreted as simply describing a perfectly natural process; it’s not really our fault, it’s simply a natural consequence of life thriving on this planet. Another is that we perceive protecting the environment only in terms of optimising the state of our civilisation. We don’t protect polar bears, the Great Barrier Reef, or whales because there is intrinsic value in doing so; we do so if it makes the biosphere more suitable for the survival of our civilisations.

I have to admit that I don’t actually have particularly strong views about this. I realise that we can’t avoid changing the climate/biosphere and that we will have to make difficult decisions. However, even though life has always changed the climate/biosphere, we’re probably the first to do so while being conciously aware of this (on this planet, at least). Hence, maybe we should take more responsibility for our actions and not suggest that this is all somehow part of a natural process. Thoughts?

The podcast with Joe Rogan is below.


Thinking like a planet (post about an earlier Adam Frank article).

Posted in Climate change, Scientists | Tagged , , , , | 74 Comments

low-probability, high-impact outcomes

Credit: Rowan T. Sutton (2018)

There’s an interesting Earth System Dynamics Discussion paper presenting a a simple proposal to improve the contribution of IPCC WG1 to the assessment and communication of climate change risks. Essentially, one can estimate the risk of some outcome by considering the likelihood of that outcome multiplied by the impact of that outcome. This is illustrated by the figure on the right (which I will discuss a bit more lately).

So, the message in this paper is that we should not only discuss the likely outcomes, but also the low-probability, high-impact outcomes. I think this makes a lot of sense. Climate change is probably irreversible on human timescales and so I think we really do want to avoid these low-probability, high-impact outcomes. Hence, it’s important that we discuss this publicly.

Credit: Michael Tobis

However, this isn’t really the first time that this has been suggested. Michael Tobis generated a figure illustrating a similar point. The public discussion seems to involve people who think climate change will be beneficial, or have minimal impact, and others who think there could be substantial costs but who avoid discussing the possibility of catastrophe. The latter may be very unlikely, but the impact would be so great that it is an outcome that we should probably not ignore.

I was going to say one more thing about the first figure I included in the post. I realise it’s probably just meant to be illustrative, but it’s not (I think) really correct. The impact really depends on how much we warm, not on climate sensitivity alone. How much we warm depends on climate sensitivity and on how much we emit. The latter probably makes this quite complicated because we can’t assign a simple probability to how much we will emit in future (it depends on what choices we make in future). The paper does mention the transient response to cumulative emissions, and emission pathways, so it’s not completely ignoring this. However, I do wonder if doing this rigorously is actually quite difficult. This doesn’t, however, mean that I don’t think this is a reasonable suggestion.

Posted in Climate change, Climate sensitivity, IPCC, Scientists, Severe Events | Tagged , , , , , , | 202 Comments