Matt Ridley’s Fourth Test

In Matt Ridley’s recent essay published by the GWPF, he says he needs to have 10 questions answered before he will think that policies to address global warming make any sense. I have tried to address his first three  questions here here and here. Matt was kind enough to leave some comments on my second response.

Update: As the GWPF moved Mr. Ridley’s essay, I have uploaded it and you can get it by clicking here (PDF). Ridley-Lukewarmer-Ten-Tests

His fourth test is “The one trend that has been worse than expected – Arctic sea ice –is plausibly explained by black carbon (soot), not carbon dioxide. Soot from dirty diesel engines and coal-fired power stations is now reckoned to be a far greater factor in climate change than before; it is a short-lived pollutant, easily dealt with by local rather than global action. So you would need to persuade me that this finding, by explaining some recent climate change, does not further reduce the likely sensitivity of the atmosphere to carbon dioxide. Certainly, it “buys time”.

It seems to me that Mr. Ridley has indeed identified an issue that climate science is late in addressing–soot is now coming to the attention of the scientific community. It changes the albedo of ice, increasing its melt. As an aerosol, it causes more warming than thought. Scientists are now coming forth with the idea that reducing black carbon in its various forms would be a quicker way to partially address human contributions to global warming than other alternatives.

This is really good news. It may indeed serve to reduce our estimates of the sensitivity of the atmosphere to carbon dioxide. It may indeed give us additional time to find solutions to this. Andrew Revkin does a pretty good job covering this here.

I would simply ask Mr. Ridley this–does he think that having extra time is equivalent to a free pass? Does low sensitivity mean we need do nothing? If abatement of soot serves as a get out of jail free card meant to end the climate debate, would it not be wise to actually abate the soot prior to celebrating our miraculous escape from man-made global warming? Remember that soot is not the only factor involved and reducing it to zero will not halt global warming.


I do not. Reducing soot, especially in the developing world, will be expensive and time consuming. I applaud the idea of doing so and would be happy to help. But in the meantime, I think it very important for those of us in the developed world to continue our work on lowering emissions of CO2. We’ve made a good start, especially in the U.S.

So, my answer to Matthew Ridley on this point is that, sir, you are correct–but it doesn’t change what’s happening in the world nor, apart from re-prioritizing our plan of attack, does it change what we should do about it.

54 responses to “Matt Ridley’s Fourth Test

  1. GWPF have shafted you by moving MRs essay.

    “is plausibly explained by black carbon (soot), not carbon dioxide” requires some kind of evidence, I’d have thought.

  2. “The magnitude of the direct radiative forcing from black carbon itself exceeds that due to CH4, suggesting that black carbon may be the second most important component of global warming after CO2 in terms of
    direct forcing.”

    “In the Himalayan region, solar heating from black carbon at high elevations may be just as important as carbon dioxide in the melting of snowpacks and glaciers.”

    As I commented on previously, while black carbon has been argued in the literature to have powerful warming effects, in the case of the Arctic there are probably multiple factors involved, such as cyclical patterns of warming (and cooling), CO2 and other factors.

    Temperature trends for Greenland, for example, show short periods of rapid warming circa 1920-1930 similar to what has been experienced recently.

  3. As far as the arctic warming, I should add one more possible cause in addition to black carbon and the other mechanisms that Will mentions. That cause is changes in circulation patterns resulting from waste heat and differential heat due to land use/land cover changes.

  4. “I would simply ask Mr. Ridley this–does he think that having extra time is equivalent to a free pass? Does low sensitivity mean we need do nothing?”
    I would like to ask, “Is co2 still the most pressing environmental problem?”

  5. TWF, I confess I don’t share your position.

    The findings on black carbon change the outlook – and policy options – considerably.

    A rapid shift to low-carbon energy sources has never been economically feasible, and still isn’t. However, it has always been a major policy position of some groups, and the primary support for that policy position has been the presumption that CO2 was by far the major driving source of warming. Furthermore, the rapid melting in the arctic has consistently been promoted as reason to believe that CO2-related warming projections have been underestimated by modelling.

    Now we find the opposite: CO2 forcing is probably overestimated in modelling. Scientific support for the economically destructive policy of attempting a rapid shift to low-carbon energy has been substantially undermined.

    From a policy perspective this is a game-changer. It tells us we can trust the most efficient mechanism for developing more cost-effective low-C technology – the market – for decades longer than we might otherwise have. It tells us that we don’t have to roll out costly immature technology in a rush to save the planet.

    • What findings on black carbon?

      When did “we” find that CO2 forcing is “probably overestimated in modelling”?

      There’s no game-changer here. You are just cherry-picking what you think supports your ideology and agenda.

    • Hi Jimmy

      First–well, hey. That’s what makes life interesting. We don’t have to agree on everything.

      Second–France went to low-carbon energy in 20 years without even much of a headache. And they prospered.

      Third–looks like some of those groups might have been wrong. I’ve been saying something along those lines for years. That’s why I’m a Lukewarmer.

      But I’m a Lukewarmer, not a Luke-cooler. I believe in markets. I also believe markets need regulation. And incentives. And a mechanism for incorporating information that resides outside of markets.

      Finally, solar’s been around for a century (look up Becquerel), wind power for several centuries and nuclear power for half a century. I do admit my proto-photonic pseudo cell capturing energy from leaf movements needs a little work…

  6. “Reducing soot, especially in the developing world, will be expensive and time consuming.”

    Time consuming yes. Expensive is always a ‘relative’ world.

    Obviously bringing the ‘power of the grid’ to rural Indians and Chinese will be expensive.

    Soot tends to be unburned hydro carbons. We get that from inefficient burning practices. Electronic Fuel Injection in vehicles has been at price parity with other methods of delivering fuel for a number of years.

  7. Investing in scrubber technology for all the new coal fired power plants in Asia rather than investing in expensive, not exactly carbon free, “renewable” energy sources would make a whole lot more sense.

    • This is actually something I’ve written about before. I have argued that especially here in California, spending on things like solar and wind power are almost vanity purchases, given their (elevated) costs. I love solar–but I think here in California we should be paying our good hard-earned money to build solar in India or China. We as a world will get more bang for the buck–materials, labor and permitting are cheaper there. We will be replacing coal or dung if we build there, instead of nuclear or hydroelectric here in California.

      Wish I had a magic pointer thingy and could say, ‘Do it my way!’

    • Most of the Chinese power plants already have scrubbers.

      Only1/2 the coal is burned in power plants.

      Steel mills, chemical plants, cement plants etc etc as well as old diesel buses,trucks etc make for a long list of what needs cleaning up.

  8. I attempted not too long ago to research what’s really going on with Arctic Sea Ice. My conclusions after a great many frustrating hours. Something clearly is happening. We can see the ice loss. For once, it’s not an instrumentation issue of trying to measure miniscule changes with shaky technology in the presence of a lot of noise. But no one seems to have much idea what is going on. Warming, black soot, etc may be making a modest contribution. But the primary cause of ice loss apparently is a change in warm season wind patterns in 2006 and thereafter that is blowing much more winter ice out through the Fram Strait into the North Atlantic than in prior years. Why? No one knows. Climate models? They don’t do sea ice. Did anyone actually predict this in any meaningful way? As far as I can tell, no. Is the change permanent? No one knows Has this phenomenon occurred in the past? No one knows.

    • what is going on is pretty well-known — Arctic sea ice is thinning and getting less extensive. The decline in extent is year-round and particularly great in the late summer/early fall.

      Climate models do include sea ice. And did predict decline in Arctic ice cover (and increase in Antarctic due to increased snow fall there — both have since been observed). Perhaps you should share what you mean by ‘meaningful way’. It’s true that the collapse has been far faster than the models estimated. Such is their bias. They also underestimated sea level rise. I’m not comforted by the models being biased towards underestimating climate change.

      If by ‘this phenomenon’ you mean did the Arctic ice pack decline to less than 5 million km^2 September average extent, then yes, we do know that it hasn’t occurred for a very long time (thousands of years, minimum). Certainly not in the last couple of hundred. Native groups in northern North America have had to develop new words for conditions (thunderstorms) now occurring, and for animals (butterflies, crickets, frogs, …) that they’re now seeing, that they’ve never seen before (in the history of their languages).

      Whether it’s carbon black, or CO2, or winds, is interesting to disentangle, but somewhat moot, as it’s a question of whether it’s human activity (throwing soot in to the air), human activity (throwing CO2 and other greenhouse gases in to the air, thence changing temperatures), or human activity (the changed temperatures driving changes in atmospheric circulation).

      Back, though, to the original: Did Ridley provide any sources for his declaration that it’s soot? If so, Tom, it’d be good if you’d provide the pointer or three.

  9. According to this graph (this link is as good as any):

    Black carbon has a negative forcing (cooling) effect of around 0.1(W/m)2.

    According to this new paper:

    The new estimated positive forcing (warming) is now calculated at 1.1(W/m)2.

    CO2 is estimated at 1.2 watts. That puts black carbon approximately on par with CO2.

    Of course, this is climate science, so everything is up for debate.

  10. Tom,

    Where does this “free pass” idea come from? I say that I need convincing that “current” climate policy makes sense. You’re erecting a straw man.

    Current climate policy largely ignores BC and is obsessed with CO2. If next time the IPCC meets, it were to say let’s urge countries to switch from coal to gas so as to do more about BC, and we recognise that bioenergy is actually not helping here so let’s urge them to stop counting it as “clean energy”, that might be a sensible thing. But the idea that I am advocating a policy of doing nothing at all is not to be found in my essay. I am saying the entire panoply of policies for subsidising wind, solar, biomass; of carbon targets that drive job creating firms out of my country; of distortions to pricing that hit the poor hardest; of diverting species conservation efforts into focus on climate change rather than invasive species; etc etc – that panoply is only justified if you can address my ten reasons why the problem is less urgent, and the cures for it more damaging, than my government keeps telling me.


    • Hi Matt

      Sorry if I’m putting words in your mouth–or in your word processor, however that works.

      I agree with your specifics–using natural gas as a bridge fuel and focusing on BC. In fact I’ve been advocating both for several years.

      And I know from your other writings that you’re speaking honestly here. But I must say none of that is in your GWPF essay–which may be its biggest flaw. I lay out some of the policies I’m willing to support in my second post on this weblog and have repeated them ad nauseum throughout the climate blogosphere. Partly (and obviously) because I want to advocate better policy than that which is currently on offer. But partly also to avoid the accusation/insinuation/whatever that Lukewarmism is about plopping ourselves in the middle of two extremes and watching the ping pong match without offering concrete solutions.

      Why not write a follow-up piece?

  11. Tom

    In reply to Robert Grumbine, you gave the wrong references from my essay for the Black Carbon point. Should be these 2:



    The Economist piece says this:

    “Black carbon is especially damaging to frozen regions, because when soot falls on snow and ice it increases the amount of light and heat they absorb. The new assessment may therefore help explain why the Arctic has been melting faster than anyone had expected. The study argues that warming is likely to be especially marked in the high latitudes of the northern hemisphere—northern Canada, Alaska, northern Europe and Siberia.”

    And I would say to Robert, it’s far from being a moot point whether it’s BC or CO2 that’s doing the extra melting. BC can be dealt with by different policies than CO2.

    Also we don’t really know enough about summer sea ice extent in the 1930s, though I’d agree the evidence probably points to less retreat than now. We know even less about Medieval or Roman summer sea ice extent. As for the Holocene optimum of 7 thousand years ago, a greater ice melt during the Arctic summer seems highly likely from the recent papers I have read, based on beach ridges in N Greenland etc. See the summary here:

    “Our studies show that there have been large fluctuations in the amount of summer sea ice during the last 10,000 years. During the so-called Holocene Climate Optimum, from approximately 8000 to 5000 years ago, when the temperatures were somewhat warmer than today, there was significantly less sea ice in the Arctic Ocean, probably less than 50% of the summer 2007 coverage, which is absolutely lowest on record.”


  12. the always interesting Tim Worstall has put some good thoughts up here about what new lower sensitivity estimates mean for policy:

    “As to what it means: it means that it’s all a much cheaper problem to deal with. The more time we have the cheaper any solution will be.

    Firstly, if we don’t have to Act Now! then we can wait until the technologies actually mature before installing vast amounts of them. It really isn’t going to be that long, wouldn’t think more than a decade, before solar is truly price competitive (40% efficient multi-junction cells for example) at which point their installation won’t even be a cost of combatting climate change. It’ll just be a natural reaction to a relative price change. The same is true of other technologies (although I’m not sure if windmills will ever make it).

    Secondly, it means that we can (or at least could) work with the capital cycle rather than against it. Rather than replacing coal plants right now, as the EU is insisting we do, we could run them until they fall apart. Replacing them with renewables at the end of their life is obviously cheaper than closing them down early.

    One way of describing this is that we move into a Nordhaus world rather than a Stern one. Instead of a medium carbon tax now, Stern’s $80, we could have a low now (Nordhaus suggests $5) but with a committment to raise it strongly to say $250 in 2040, 2050. There’s very little of our energy infrastructure that won’t be replaced anyway before 2050, but this would allow us to get the most use out of what we’ve already built and paid for.”

    • Worstall is just parroting other peoples error in thinking that less-than-2-oC-is-now-likely.

      You really are in trouble if you start taking your science from Worstall.

    • My recommendation (taken from Lomborg circa 1998) for carbon tax is $12/ton.

      I think Mr. Worstall hasn’t grasped the implications of recent publications. It doesn’t change so much the range of possible sensitivity values–those who really are desperate to think they’re at the upper end will continue to do so, and those who think it’s minimal probably will, too.

      What’s happened is actually more important. By chopping off the fat tail we can actually plan for the medium term. Before this, every time someone came out with a practical suggestion for relocating roads, building a sea-wall or changing insurance schemes for flood plains, some alarmed activist would show up and insist that the low-probability, high-risk possibility of extreme warming be included in any plan, thereby making planning too expensive and complicated for mere humans, even those aided by computers.

      New calculations reducing the possibility of these low-probability, high risk outcomes brings both adaptation and mitigation within the realm of human action and real-world budgets.

      Far more important and far more encouraging that just a shift in the center range of potential values for sensitivity.


      • “My recommendation (taken from Lomborg circa 1998) for carbon tax is $12/ton. ”

        Anyone in 1998 predicting that global seaborne coal prices would be $100/tonne in the year 2013 would have been carted off to the insane asylum. The price of coal had been declining for 20 years and everyone…absolutely positively everyone predicted that the price would continue to decline.

        Everyone was wrong.

        We don’t need a price on carbon. We can see it in the number of windmills, solar panels, hydro dams and nuclear power plants the Chinese are building.

      • Hi Harry,

        Think of a carbon tax as an emphatic hair shirt, then. I believe we need a (revenue neutral) financial signal to large-scale emitters that we recognize negative externalities associated with emitting CO2. I think we want to spur utilities to move away from coal, innovation in cement production, further development of electrically powered transportation.

      • Tom,

        Alternative fuels for cement production…

        In countries like Japan, USA, Denmark, Netherlands, Switzerland and Belgium sewage sludge is used in cement production.

        The first ‘demonstration’ plant of using sewage sludge to make cement was set up in China in 2009.

        Obviously…the amount of press coverage being given to the various uses of sewage sludge in building materials is limited as some people may have objections to using cement made from sewage.

        There is a reason the Chinese Government can say they expect coal consumption to peak in 2015. There is a lot of room for dramatic improvement in cement.

      • Hi Harry

        That’s cool–and it’s news to me.

    • I am given to understand that congratulations are in order, m’lud. Congratulations!

  13. Dick:
    The summary and scientific sources are at:

    Where in the 286 page pdf from JGR did you find them attributing most or all of the Arctic sea ice decline to black carbon. The most apt comment I find
    on blog-speed reading is on page 122:

    8.6. Detection and attribution of climate change due to black carbon
    [24] As Sections 8.3 to 8.5 have outlined there is evidence of regional
    climate responses to BC that is manifest in observations. In particular,
    there is some evidence for a BC effect on: 1) regional temperature and
    precipitation changes [e.g., Menon et al., 2010], 2) Arctic temperatures
    and snow-ice cover [e.g., Flanner et al., 2009; Koch et al., 2011b],
    3) monsoon and other circulation changes [e.g., Rotstayn et al., 2007;
    Bollasina et al., 2011; Shindell et al., 2012] and 4) Himalayan and
    North American snow and ice cover [Qian et al., 2009 Qian et al.,
    2011]. However, it should be noted that none of these studies formally
    attribute changes to BC in a statistically rigorous sense.

    There’s a long road between ‘an effect’ and ‘is the cause’, as
    the authors note themselves.

    The Economist is not a science journal, so please don’t refer to that.
    Non-science magazines say all kinds of things about science. The JGR
    paper is interesting and I may take it up at my blog.

    We can do a more direct look, if crude and back of the envelope, at
    whether and how much of the Arctic sea ice decline is due to the black
    carbon effect. The authors estimate (global average) effect of
    black carbon on sea ice and snow on sea ice at 0.01 W/m^2 (with large
    error bars). The arctic is about half the sea ice in the world, giving
    it, say, 10 million km^2 annual average. That’s 0.02 of the globe,
    so the local effect is more like 0.5 W/m^2 (with even larger error bars).
    A rule of thumb that I use (in part because it’s pretty close) is that
    1 W/m^2 for 1 year means 1 meter of sea ice. So the black carbon, at
    this central figure of the authors’, is melting a meter of ice every
    2 years, 5 meters in the last decade, and 25 meters in the last 50 years.

    Oops. 50 years ago, the Arctic pack averaged not quite 5 meters
    thick. If black carbon were a prime factor in ice’s decline, the pack
    should have been obliterated each summer for the last few decades.
    The fact that it hasn’t been suggests that the estimate is either
    more than a factor of 5 too high, or that the radiative forcing at
    the tropopause (the figure they’re actually working with) is more than
    5 times greater than the surface effect. Or, of course, some combination
    of the two.

    The much simpler observation that black carbon is not a prime factor
    in the decline of Arctic sea ice is to observe that the decline only
    surfaces in observation in the last 10-15 years, while significant
    black carbon (as with sulphate) emissions have been with us for
    60ish years.

    Then you go to matters of us not knowing ‘enough’ about sea ice extent.
    Put something on the table. How much is enough, and when did we first
    gain the ability of know enough? How did you decide that was the
    requirement? Take a look at my note for some of the sources.

    Press releases are even less reliable than magazines. Let’s talk
    science, not press release. Cite the actual papers, that you’ve read,
    that support your claims. Anyhow it’s odd that you claim that we don’t
    know enough about 1930 sea ice, yet are trusting claims about sea ice
    8000 years ago. Is it easier to observe the paleo ice cover?

    That aside, for the sake of discussion let’s say that the Arctic
    really was seasonally ice free 7000 years ago. So what? What do you
    conclude from that?

    • Hi all,

      As someone who has been caught in this sort of a crossfire of competing requests for sourcing and calculations (even put in a very cordial tone, as by Robert), I want to raise a hand in Matt’s defense here.

      Matt is clearly taking advantage of recent publications on the subject to further his overall case and although the questions put to him are valid and should be answered, he may not have had time to formulate a response in advance and may not feel qualified to do so.

      Robert, I like the way you have formulated your response–laying out the implications of these claims (which remember, didn’t originate with Matt) is an excellent way to direct the discussion.

      Let me ask you this–how well traveled is black carbon? My understanding is that the geographic origin of much of this black soot actually counts–that for example, American contributions 50 years ago might not have made it to the Arctic while current emissions from China may well have.

      As an aside, I do not want to take the discussion of recent news off the table. I think it’s legitimate to write about press releases. The scientists and organizations that issue press releases surely want them discussed. If there is the potential for exaggeration and misinterpretation of their news then surely it is incumbent upon them to discuss implications, just as you have here. Instead of ruling them out of order for blog discussion, let’s perhaps provide the background and implications that they should have.

      And I understand that makes for more work for people like you, Robert. But limiting discussion to the well-understood and thoroughly digested ain’t as much fun.

      • Robert, another question regarding BC and ice. Would BC be more ‘effective’ as a melting agent if combined with other warming factors? If atmospheric or ocean warming had primed ice to be vulnerable, would the last decade’s emissions of BC be the straw the broke the back?

      • Tom:
        Matt’s a big boy and can respond to, or ignore, requests for sources and clarifications as he sees fit. imnsho. No need for you to protect him from me.

        But it’s curious that you step in to defend him, and not me, when I was, myself, asked to provide scientific support for a science statement I’d made. Dick had every right to do so, I think. For the same reasons I think it’s fine for him to ask me, I think it’s also fine for me to ask someone else.

        This is your table, though, so your rules. Since you’re ok with me being asked to provide sources, it looks like rather a biased table we’re sitting at. I
        tend not to stay in such places.

        My impression was that this series of yours was to be looking at science in response to science questions of Ridley’s. If so, it strikes me as perfectly reasonable to ask him about his questions. If he doesn’t feel qualified to answer, it’s really for him to say. The idea, right, was that these were science questions he wanted answered before agreeing to action w.r.t. climate change. By all means, of course, discuss news, press releases, op-eds to your heart’s content. That wasn’t how you presented this series, however, which was much of why I bothered to comment.

        The black carbon paper Matt referenced, and I’ve looked through (i.e. I took time from other activities to engage in a serious discussion rather than merely engaging in blog debate (see for the importance of those words for me). Serious discussion includes that we all can be asked for sources, and have expectation that those sources will be read prior to the next iteration.

        As my examples and questions to Matt illustrate, black carbon is far from a “well-understood and thoroughly digested” matter, so I’m rather baffled by that last comment of yours.

      • Hi Robert,

        Well as I think you’re most probably correct I didn’t think you need defending. As I think Matt is approaching this from outside a strictly scientific approach (which I would also defend as his right–remember that I’m not a scientist either), and as I have disagreed with him on two of his essay points, I thought it appropriate to at least defend his approach.

        I think asking for sources is perfectly legitimate and I don’t think there’s anything wrong in you doing so. I also think not having them immediately to hand is okay. If Matt were not a rather famous writer with an active schedule I would expect him to say ‘I’d better check this out and will get back to you with what sources I have used or can find with a reasonable amount of effort.’

        I didn’t start this weblog with the intention of this being a place where those conversant with many elements of the science at a detailed level (such as yourself) could engage in reasonable dialogue with those looking at the policy impacts and political decisions on the table (such as Ridley), but I sure wouldn’t mind if that happened.

        To recap: I think you are correct to ask Mr. Ridley for references. I think it understandable if he cannot immediately produce them. (If I were he I would ask for help–lotsa smart people have come by and visited here.)

        I do hope you stay.

  14. Ah well. We see that your proffered excuse of Matt not having enough time, even to comment that he needs time to find his notes, is off the mark, as he has responded elsewhere on your blog.

    In wondering why ‘scientists don’t engage’, it’d be good to keep in mind that it takes two to engage. When the non-scientist flees elsewhere, it is not the scientist’s fault that there’s no engagement.

  15. Cleaning out my email boxes, coincidentally a year later. I see no response from Ridley, nor Fuller. How many years should Ridley be allowed, and still to maintain a pretense that he’s at all concerned with reality on the topic?

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