Volcanoes, Not Pollution, Slow Global Warming

By Tom Yulsman | March 1, 2013 2:54 pm

An astronaut aboard the International Space Station captured this dramatic photograph of Sarychev Volcano in an early stage of eruption on June 12, 2009. The volcano is in the Kuril Islands, northeast of Japan. (Photo: NASA Earth Observatory)

If you pay attention to global warming skeptics, you’ve probably heard the oft-repeated meme: global warming has stopped. It’s not really true, of course. (More on that in a minute.) But there is evidence that over the past 10 or so years, the underlying rate of warming has slowed.

What gives?

One hypothesis has pointed to a 60 percent upswing in sulfur dioxide air pollution from coal burning in China and India. Sulfur dioxide aerosols act like a parasol to reflect some of the sun’s energy back into space, and thereby cause cooling.

But new research published today shows that sulfur dioxide aerosols spewed into the stratosphere by moderate volcanic eruptions have been a significant reason why warming has slowed.

The research was led by Ryan Neely at the Cooperative Institute for Research in Environmental Sciences, and it has been published online in Geophysical Research Letters. (Disclosure: The University of Colorado, where I work as co-director of the Center for Environmental Journalism, is a partner in CIRES.)

Previous research has suggested that increasing shading from aerosols in the stratosphere has offset about 25 percent of the warming caused by human emissions of carbon dioxide and other greenhouse gases. To determine the roles played by pollution from coal burning and volcanic eruptions, Neely and his colleagues used computer modeling. And as part of the work, they included data on volcanic eruptions between 2000 and 2010 — including Sarychev Volcano in the Kuril Islands, which blew its top on June 12, 2009. That’s the one in the picture at the top of this post, shot by an astronaut aboard the International Space Station. (For a short but incredible video, click  here.)

Neely says the 2000 to 2010 period has been unique “because it was the first full decade or longer that we had extensive observations of the aerosol layer that were not perturbed by a large eruption” — one like the gargantuan Pinatubo eruption in 1991. “In light of this, we were able to study the ‘background’ state of the straotosphere aerosol layer for the first time and start to understand how smaller volcanic perturbations, and humans, may be impacting it. What we found was that, over this decade, moderate volcanoes drove the variability.”

What about the claim that global warming has stopped, or that the planet has even been cooling? Not true says Neely:

Climate change has not stopped.  We are still emitting massive amounts of greenhouse gases, and that increase will cause the temperature to rise. This has been known since the late 1800s and is pretty basic science.

More to the point, Neely says climate trends need to be evaluated over a period of time long than just ten or 15 years:

Due to the intrinsic variability of the atmosphere, one cannot draw any conclusions over such short periods. What we have shown is that moderate volcanoes (smaller than previously thought were important) play a role in this variability by slowing the warming that we would have expected to see if the only thing changing was the amount of greenhouse gases.

But volcanoes aren’t the whole story:

Other forcings have also helped to slow the rate of warming over this period, and if you add them up they help explain the decadal variability we are seeing. Because regional and short-term scales are the ones that have impacts on our lives, we need to understand all the players in the details of the variability better so that we may make better predictions of climate change on these scales. This study had contributed to this understanding.

  • Salaminizer

    I blame Al Gore.

  • Doug Allen

    “But climate change hasn’t stopped” is a stunningly evasive answer to the question of whether the warming has now paused for 15+ years. Furthermore, climate change never stops, does it? While it’s possible that aerosols have increased (we don’t have enough data to know) and have countered whatever warming otherwise might have occurred from increasing GHG, it’s just as likely that solar and PDO have been the recent dominant forcings. Even more likely is that climate sensitivity is lower than the AR4 3 degree C mean prediction. And about the need for over 15 years. Yes, we need much longer to invalidate climate sensitivities of 1 degree C (the climate sensitivity based on atmospheric physics with no feed backs, and I doubt that will happen), a while longer longer to invalidate climate sensitivities of 2 degrees C, but 15 years has already invalidated the the 3 degree and higher climate sensitivities at the 95% confidence level. Climate is a fascinating puzzle. Let climate science figure it our. There’s no longer any reason to think we have to act now.

    • http://www.facebook.com/tom.yulsman Tom Yulsman

      There are a number of possibilities. It may well be true that a given amount of CO2 will produce less warming than scientists have thought. But it may also be true that scientists have developed a pretty good understanding for why warming has slowed — natural variability plus volcanic aerosols, with the current study showing that the latter is very important.

      In other words, we can’t say for sure what will happen. Perhaps we’ll get lucky and you will be right. But there is a good chance that you will be wrong.

      Science can’t tell us what to do about this. The policy path your or I favor depends on our beliefs and values. I believe, based on my understanding of economics, that any possible negative short-term consequences of enacting a gradually rising carbon tax and using the revenue to make greater investments now in energy efficiency and carbon-free energy would be more than paid back in the long, in multiple ways.

      Given my values, I would rather make those investments now in an effort to avoid the real risk of saddling my children and grandchildren with consequences on the extreme end of the spectrum, even if we cannot say for sure yet exactly how likely those extreme consequences may be. The risk is real, and I think we have an obligation to do what we can to avoid it.

      If we wait to be surer, and it turns out you are wrong, it will probably be too late to do anything but adapt. (And in some scenarios, adaptation would be quite difficult.) Whereas there is still some time to work on both mitigation and adaptation.

      Much climate change is already in the pipeline no matter what we do now. But some of the most extreme consequences might still be avoided. And I think based on what we know now, the risk of those consequences occurring are high enough that we have a moral obligation to future generations to choose that path.

      I realize that the issues are enormously complex. And people whom I respect, but disagree with, think differently. I also realize that given our nature as human beings, as well as two other factors that loom very large — namely, India and China! — that we are probably not going to be very successful at mitigation and that we’ll be left with having to adapt. In that case, we can only hope and pray that you are right in your assessment of the risk. I fear that you are not.

  • Buddy199

    we need to understand all the players in the details of the variability better so that we may make better predictions of climate change on these scales…


    Before we institute massive governmental intervention by way of far reaching regulation, tax increases, energy market manipulation and attempting to completely upend the global industrial economy.

    • Sean

      There is nothing wrong with being more sensible with energy and air quality now. Your analogy is flawed, a doctor is going to tell you, for example, dont worry about exercise and diet until I find out whether your obesity is caused from a thyroid condition, psychological effects, etc. And to sit on your hands until we understand all the players (variables) in a system as complicated as earth is a cop-out. Our most powerful computers can’t even predict the weather 4 days away what exactly are you expecting and when?

      • Buddy199

        That is the point. If the models can’t even make accurate prefictions 4 days into the future how can they make accurate predictions 100 years into the future. Just “doing something!” might make you feel better. But it is a ridiculous course of action if you don’t understand the nature of the problem your “something” is attempting to fix.

        • http://www.facebook.com/tom.yulsman Tom Yulsman

          Buddy: There are significant differences between weather and climate. By definition, weather consists of what is happening in the atmosphere over the course of hours and days. And since we want to know whether to put on a down jacket or a light fleece, weather forecasts have to predict the very fine details about what is going to happen to temperature, atmospheric pressure, winds, humidity, precipitation, etc. over relatively small geographic scales. Even though this is a very complex difficult task, forecasting has become much more accurate, thanks to sophisticated meteorological models. Even so, small errors in initial conditions can make a big difference in the forecast.

          By contrast, climate is the long-term average of weather. You may have heard this expression, but it bears repeating: Weather is what you get, and climate is what you should expect.

          Computer modeling of the future climate is not intended to produce the very precise weather conditions that we might expect in your neighborhood or mine 50 years hence. They tell us what average conditions to expect — and over a much broader geographical range than weather models. For example, computer modeling of the climate predict that dry areas of the world will get, on average, drier still; and wet regions will become even wetter. So far, observations show this prediction about average conditions over broad regional scales is holding up.

          So the comparison you are making between weather and climate really is not valid.

          Thank you for commenting here. And I hope you will come back.

          – Tom

        • Sean

          You missed the point. I dont need a computer to model smog – look out your window. Look at the sat photos of the ice caps sea levels etc. These are facts not predictions. Co2 is a green house gas and holds heat walk into a greenhouse on a winters day. Visit a landfill one day and see what could have been recycled or reused instesd of dumped. The something I choose to do is be more responsible. Good luck to you.

  • http://www.facebook.com/jonah.gercke Jonah Gercke

    We don’t need the Supreme Court to tell us carbon dioxide is a pollutant — we just have to look at our changing world. http://clmtr.lt/cb/pyR0HO

  • Nullius in Verba

    “This has been known since the late 1800s and is pretty basic science.”

    I don’t know why, but it still depresses me when even science journalists say things like this without themselves having any actual understanding of the physics. Surely they must know that science doesn’t work like that. If the science is that basic, then tell us what it is. Don’t just quote an expert asserting it and assume everybody will trust that. Not just because a lot of people won’t, but because some people will, and will conclude that the way to learn about science is to blindly trust the assertions of experts, an error which others can exploit.

    You usually have people on one side who don’t understand it listening to one set of experts arguing with people on the other side who don’t understand listening to a different set of experts, each side shouting about how the other side is “unscientific” for trusting the wrong experts, although how you’re supposed to tell the difference without understanding the science beats me. Well done on not doing that, at least! That’s actually very good!

    For what it’s worth, the science isn’t basic, and it wasn’t known until the late 1960s. The version of the physics they had in the late 1800s was wrong, and had been proven to be wrong by around 1904. It’s highly unlikely you’ve ever been told the correct version – it’s not often presented to the public. (And the big issue is not the physics of the greenhouse effect anyway, it’s the physics of the feedbacks, which is a totally different question and definitely not simple.)

    For anyone who thinks they do understand the physics of the greenhouse effect, there’s an easy way to tell. If you are given the information that liquid water absorbs all thermal infrared within about a millimetre (and is obviously transparent to visible sunlight), can you calculate from that the rough magnitude of the greenhouse effect in a sunlit black-bottomed pool of water a metre deep?

    It’s actually a far easier calculation than the corresponding one for Earth’s atmosphere – instead of requiring thousands of lines of quantum mechanics to determine all the absorption lines at every level, it can be done easily on the back of an envelope. Don’t forget to show your working!

    So, after you’ve had a few minutes to think about it – do you still think it’s pretty basic science?

    • http://www.facebook.com/people/John-Hartshorn/716849760 John Hartshorn

      Maybe you can explain how quantum mechanics figures into this?

      Of course the details of how much and when are complex, but the basic facts about CO2 and other anthropogenic gases causing a heat buildup are not all that big a deal. Maybe we are still refining our knowledge, but the basic principle has been understood since Arrhenius first elaborated it in 1896.

      Arrhenius’ formula, ΔF = α Ln(/), where is carbon dioxide (CO2) concentration measured in parts per million by volume (ppmv); denotes a baseline or unperturbed concentration of CO2, and ΔF is the radiative forcing, measured in watts per square meter. The constant alpha (α) has been assigned a value between five and seven. His estimate of a 5-6 degree C. temperature increase for a doubling of CO2 was at the upper end of the range that contemporary research is projecting.

      It just took a century for folks to accept that he was on to something.


      • Nullius in Verba

        Quantum mechanics figures because that’s how you calculate the wavelengths, strengths, and widths of the absorption lines. Molecules in a gas can only absorb photons if the energy exactly matches a gap between two quantum energy levels. Absorption in solids and liquids get smeared out because of the interactions between the molecules allows many more transitions.

        “but the basic principle has been understood since Arrhenius first elaborated it in 1896″

        That’s the point – everybody says it, but it isn’t true. The physical principle Arrhenius used is incorrect. He got (sort of) the right answer but by the wrong method. Angstrom criticised several of the claims in 1900. The basic physics was shown to be wrong in 1909 (a physics professor called R W Wood performed some experiments on greenhouses that didn’t block outgoing infrared, and found they were no less effective), and the hypothesis was abandoned until work in the 1950s and 1960s eventually led to an alternative physical mechanism that also predicted a warming and is physically valid.

        It wasn’t until the 1950s that they developed computer models able to perform the calculations in detail, and Manabe and Strickler demonstrated in the 1960s that the Arrhenius mechanism, if it actually applied, would produce an average surface temperature on Earth of 60 C. Since it’s actually about 15 C, the theory is falsified. If you had performed the calculation I suggested, you would have seen that it’s falsified even more dramatically by a simple pool of water, which according to Arrhenius’s theory should produce an intense greenhouse warming.

        However, Moller, Manabe, Strickler, and Wetherald produced an alternative model of the greenhouse effect that did correctly predict the surface temperature, and was also able to explain the atmospheres of other planets, pools of water, and other effects. It was based on equations developed for stellar atmospheres (i.e. the insides of stars) by Schwarzchild in the 1930s.

        What I find fascinating is the way everybody keeps on repeating the theory that’s wrong, telling everybody how it’s really simple physics, and nobody in the mainstream science communication community has noticed. Nobody has noticed how those greenhouse-in-a-bottle experiments they show to schoolkids are wrong too. I find it weird, and it makes me wonder how it comes about. I mean, we do teach people how science works, right?

        None of this should be taken as saying the greenhouse effect doesn’t exist, or that climate scientists don’t model it correctly, because it does and they do. As I said, they’ve known since the late 1960s. It’s only the explanations to the public that are a problem. It’s the question of how a wrong explanation on such a critical and high-profile public issue could be so widely promoted without any of the people promoting it noticing that the explanation was wrong that I find intriguing. There’s some interesting psychology going on here.

  • http://blogs.discovermagazine.com Celine Roig

    This may be a bit outside the subject matter but I think volcanoes could be great incinerators of our garbage that is piling up our landfills.

    • Charles Calhoun

      The gods would not like the volcanic sacrifice to be in the form of
      table scraps, old plastic bags and dirty diapers. Not to mention the huge transport costs.

      But, and a big but, the reduction in global volcanic activity along with the massive reduction of the
      rain forests in central/south america and the south pacific are really the greatest contributors to the minute and perhaps transitory warming effects we have seen.

      Al Gore does not have to worry about the local temperature anymore, he can fly his jet to where ever he wants since he cashed out to Al Jazeera.


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ImaGeo is a visual blog focusing on the intersection of imagery, imagination and Earth. It focuses on spectacular visuals related to the science of our planet, with an emphasis (although not an exclusive one) on the unfolding Anthropocene Epoch.

About Tom Yulsman

Tom Yulsman is Director of the Center for Environmental Journalism and a Professor of Journalism at the University of Colorado, Boulder. He also continues to work as a science and environmental journalist with more than 30 years of experience producing content for major publications. His work has appeared in the New York Times, Washington Post, Audubon, Climate Central, Columbia Journalism Review, Discover, Nieman Reports, and many other publications. He has held a variety of editorial positions over the years, including a stint as editor-in-chief of Earth magazine. Yulsman has written one book: Origins: the Quest for Our Cosmic Roots, published by the Institute of Physics in 2003.


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