Reduced Sulfur Emissions Could Cause Climate Shock

When we talk about emissions these days, we typically talk about cutting them back for the good of the environment. However, the climate system is a complex beast, and one we’re still learning to understand.

As it turns out, cutting back on emissions may have unexpected or undesirable effects. Some scientists are concerned that cuts to human-induced sulfur emissions may actually be warming the Earth.

What’s The Deal With Sulfur Emissions?

The G.G. Allen Steam Plant features a large scrubber to reduce sulfur dioxide emissions from the plant. These are common in developed countries to reduce pollution. Credit: Murr Rhame, CC-BY-SA-3.0

Much work has been done over past decades to cut down on sulfur emissions. This has taken many forms, but often comes down to targeting fossil fuel sources. The European Union, United States, and many other jurisdictions have legislated lower sulfur levels in diesel fuels. This has led to cleaner engine designs with emissions control devices that rely on lower sulfur levels to work. Similar efforts have been made to cut sulfur levels in marine fuels as well. Many coal plants have also cut down on emissions of sulfur dioxide, through the use of flue-gas desulfurization hardware.

Cuts to sulfur emissions have been made with good intentions. SO2 and other oxides of sulfur (SOx) are harmful to human health. High levels of sulfur oxides in the air can harm plant growth, and these emissions also have a habit of causing acid rain, too.

However, as it turns out, sulfur emissions tend to help create sulfur-based aerosols that end up in the stratosphere. These aerosols actually increase the amount of sunlight reflected away from Earth. In this way, they have a cooling effect on the planet – quite the opposite of greenhouse gases like carbon dioxide and methane.

Overall, the efforts to cut down on sulfur emissions have been successful. Over time, more and more countries have switched to cleaner low-sulfur fuels, and the maritime industry has been proactive in following suit. In particular, sulfur emissions from the shipping industry have dropped 80% worldwide since 2020. The effect has only been compounded by the abrupt drop in shipping activity experienced in the first year of the coronavirus pandemic.

So What’s The Problem?

The problem is that the aerosols produced by sulfur emissions were probably doing good work cooling the Earth. As our greenhouse gas emissions have continued to ratchet up over the years, the cooling effect of our sulfur emissions may have hidden some of the damage being done.

With such a rapid reduction in sulfur emissions, we may face something called an “aerosol shock” or “termination shock.” This is where the Earth’s climate rapidly heats up once the production of cooling aerosol is terminated. This can have rapid and catastrophic impacts on the climate, or at the very least, unexpected ones.

Unfortunately, our understanding of aerosols is limited at this stage. Models show that the impacts of reduced sulfur emissions could be unmeasurable, or could be serious and severe warming on a regional or even global scale. That’s a wide range of options, showing that we need to better understand the problem before we can be sure.

Acid rain is just one of the many negative effects of sulfur emissions. Thus, reducing sulfur emissions is necessary, but may not be without consequences. Credit: Nino Barbieri, CC-BY-2.5

However, we do have some measurements that indicate there may be a real problem here. Comparing 2014 to 1750, the estimated cooling effect of aerosols on the Earth was to cut roughly 1.3 watts of solar energy per square meter (W/m2). By 2019, that had dropped by 15%, to just 1.1 W/m2. That’s a significant amount.

There’s some correlation in data from past decades, too. As Europe began to cut sulfur dioxide emissions from the 1980s, it has seen an uptick in temperatures. Correlation does not equal causation, of course, but it’s an area worthy of further investigation.

It’s part of a broader trend in Earth’s albedo, the amount of light it reflects back to space. Less aerosols and less ice on Earth are both making the planet less reflective. That means the Earth absorbs more heat, leading to higher temperatures. It’s feared that rising temperatures could push further change to albedo as glaciers and ice sheets melt, locking in a runaway increase in temperatures beyond our control.

Can’t Turn Back The Clock

Of course, this isn’t to say we should ramp up sulfur emissions to cool things down. That would cause harm to health, likely dampen crop yields, and increase incidents of acid rain, among other negative effects.

Plus, aerosol shock is a primary reason many say we shouldn’t intentionally use aerosols to cool the climate. If we relied on aerosol production to counteract global warming from greenhouse gases, we’d be in big trouble we had to stop all of a sudden. Whether due to politics, mechanical failure, or some other cause, we’d be exposed to sudden ramp up in temperatures that would play havoc with the climate.

The fact that sulfur aerosols may have counteracted some warming effects is notable, but by no way a solution for the problem of climate change. Instead, it should serve as further incentive to drastically cut back on greenhouse gas emissions. We may just have to work harder than expected in order to account for the fact that sulfur-based aerosols may have been obscuring the worst consequences of our excesses.

[Headline image: “Sulfur Fumarole” by USGS.]

53 thoughts on “Reduced Sulfur Emissions Could Cause Climate Shock


    Human climate engineering is an industry that we need to create. Controlling the temperature and rainfall of our planet is a step toward becoming a next level civilization. We lack the will to do what is needed to control the planet’s temperature. We don’t lack the knowledge.

    If we don’t do what is needed to do these things, as the temperatures rise naturally as the sun expands NOTHING will prevent our demise. CO2 isn’t going to go away immediately. Those that talk about capture are just looking for grant money.

    1. “We don’t lack the knowledge.”
      Yes you absolutely do. This is called hubris. If you think that introducing technocratic managerialism to the climate will have only good outcomes, you have not been paying attention to anything.

      1. Indeed, we know just enough to have some idea of the results of any one action.

        But not enough as this article rather clearly shows to really manage such a complex web of connections. Even if this sulfer aerosol cooling pans out to be more co-incidence than real once the science is further understood the fact we are only NOW noticing it might be a factor…

        There is only one state we can be pretty sure from available evidence is sufficiently stable for life as we know it to thrive on Earth longer term – and that is the condition when nature gets largely free reign and is doing the regulation itself with fewer pesky humans and rather less industrial activity. As we know for many centuries of this climate changes were rather slow, to the point everything can adapt or migrate and its doubtful the great great great grandkids would be able to notice any change at all…

        Obviously we can’t just go back to hunter gatherer species, or small footprint for lack of population now – which means we may have to progress to pulling the levers of climate regulation to make up for the unstable mess we have made of the natural order – in the same way we cull deer in the UK as there are no longer any apex predator to keep the numbers under control. Doesn’t however mean we really know what we are doing, and we can’t continue to be so reckless going forward, once you are balanced near the edge of a cliff its time to start really paying attention to your footing, testing each step before taking it and hopefully finding a path leading a bit more inland..

        1. There have always been very sudden, quick temperature changes (dixit every climate change denier) due to volcano eruptions and giant meteorites.
          A recent one was 1815 (, where the global summer temp dropped .4-.7°C, more in Europe, causing food shortages and famine. So we could geonengineer our way out of global warming by just putting soms dynamite sticks in a dormant volcano (heck, why not nukes!) but this would cause other problems unless everything was understood (it isn’t) and we could carefully control it (we can’t even predict vulcano eruptions). So good luck.

          1. Yeah! That is a great idea!..

            To fill the atmosphere with choking often rather nasty dust, block out lots of sunlight for prolonged periods, and when it settles potentially drastically change the soil composition so the crops likely won’t grow well either.

            As I said ‘sufficiently stable’ – as in variations have occurred. Which as you point out is actually a good data point or two for what might happen if we do x, but far from enough to actually know how the complex interdependent web of other important details will change.

          2. Yeah, but volcanic eruptions have been short anomalies. Now we’ve heated the environment for decades and the sea for example will keep releasing that warmth for centuries.

      2. We know how to manipulate temperature. We know how to reflect sunlight, We know how to block sunlight. We know how to move water to dry areas. We know how to move water from flooded plains.

        We know enough to start figuring out the science of controlling our destiny. It’s not hubris. It’s lack of imagination and greed that keeps us from being able to clean up how we do things.

        If we wait for the one answer that fixes everything, we’re in a world of trouble.

        We need to begin experiments to see what the overall effects of what we do will be. Start with changing the rooftops of a city to a reflective material. And perhaps move flood waters from areas that consistently flood to help areas that do not.

        We won’t solve this problem just by driving electric cars. We won’t solve it by building solar panels and wind farms. Even Nuclear is not the ENTIRE answer.

        But much of what we need to do to fix this or get it under some level of buffered control requires POWER to do it.

        Sure, my statement isn’t the entire fix, but to outright say we lack the knowledge to mitigate the problems we’re seeing is inaccurate. We know some of the puzzle. I’m suggesting we start on the corners and get this jigsaw together rather than wait for all the pieces to arrive and hope for the best.

    2. Another terrible idea like “iron fertilization” which wasted decades only to turn out as a dud:

      Stop introducing new chemicals to the eco system. The eco-system self-regulates, since billions of years. Just produce less CO2. It’s so easy.
      Also if we want to start pointing fingers, real nice China secretly produced CFCs illegally for decades.

      1. Better idea: make biochar / Loma Prieta, out of lots of crappy waste vegetation, and bury it in farms. Sequesters carbon for millennia, and absorbs fertilizer and excess water.

    3. Rumours of our demise are wastly exaggerated. Granted, the tropical and subtropical zones are losers in this, but subarctic and arctic zones gain from the heating. Humanity aint going nowhere, just have to scale down on the population.

      1. Even if you assume we broke the world just enough to make the frozen wastes more inhabitable, but not too fast giving some folks enough time they can manage to transplant plant and animal life sufficient to create a sustainable life for themselves they in short order AND in secret so everyone else fleeing the hellscape of our own making won’t be turning up wanting it for themselves, they still will not really be human as we understand it now. Being rather too busy trying to scrape a living out of the rather hostile environment they managed to create to keep educating – as soon as you take education and so much historical knowledge away a human is very much just a monkey with untapped potential… So yeah the genetic identity of homo-sapiens might manage to survive, but the folks that do so are not likely to really remain human in any way we would recognize…

      2. Going nowhere is the sticking point. How’d you think Russia would react if all the Chinese want to relocate north. Or Canada for that matter when every yank wants to emulate his southern neighbors!

  2. An interesting development to say the least.

    Perhaps mixing in a bit of sulfur into jet fuel is a “solution”? After all, distributing it at 10-12 km above AMSL is a lot better than most industrial users and shipping industry is able to. And down low the sulfur isn’t as useful. (unless some of the requirements needed for it to do its job only happens closer to the ground, then things gets more complicated.)

    However, it also highlights a big thing with any policy or decision. And that is unforeseen consequences showing up slowly over time. There though isn’t many ways to make research to see changes ahead of time, the Earth is a very huge complicated system, and small scale experiments and even simulations aren’t always that helpful.

    But like any system, one can nudge it in a given direction, observe changes, and rethink one’s decisions if they were for the better or worse. Though, politics and public opinion isn’t one to follow drastic changes in policy, and there is frankly too many pieces in play to get a good grasp of the larger picture and what decisions are actually good or bad. So when politics and public opinion have been pushed down a given track, it can be hard to get it to alter course.

    At least clear research of the effects of various things is helpful. And perhaps sulfur emissions have been reduced too much at current. If emitting more is “better” is though debatable.

      1. I am partly curious to what “doing this” refers to?

        Reducing sulfur emissions?

        Blending sulfur into jet fule? (this is something I am curious to what the effects would be, so I hope people have information about this.)

        Trying to swerve political and public opinions on the topic and having people react unexpectedly?

        Basing policy on small scale tests and making rash conclusions from what in fact were noise or bias from external sources?

        One can likewise ask who “they” are…

        I am just curious about this ambiguousness. (or is it just laziness in not desiring to type a few more words as to remove most of the risks of misinterpretations?)

  3. “Cuts to sulfur emissions have been made with good intentions. SO2 and other oxides of sulfur (SOx) are harmful to human health. High levels of sulfur oxides in the air can harm plant growth, and these emissions also have a habit of causing acid rain, too.” There is a series of the videos on the video site. I have only seen the first three but they are hillarious and worth the watch.

  4. Second sentence of the second last paragraph, I think there is a word missing. “[…] in big trouble we had to stop all of a sudden.” reads better if it is “[…] in big trouble [if] we had to stop all of a sudden.”

  5. Not a problem. The cloud of microsats and nanosats being launched should soon put us in perpetual twilight. More videos and social networking and and cellphone connectivity and save the planet at the same time. The massive reduction in our collective IQ shouldn’t matter much.

  6. There is a very good reason why a lot of people don’t listen to this alarmism anymore. This is a real Boy Who Cried Wolf situation.

    Environmentalists have been going on about how the world is going to end since the late 1800’s. (There’s lists of predicted Environmental End Of World Events. The propaganda keeps changing every 5-10 years.) They keep saying we’re going to kill the planet unless we do some societal wide, usually government engineered, mass shift in behavior to live like pre-Industrial Revolution times again. These people are extreme authoritarians. Instead of promoting environmental consciousness, be less wasteful, and be more self-sufficient, they want to force their ideas and lifestyle onto everyone, usually by saying “my science\study proves it”.

    The people that don’t listen to environmentalists aren’t evil. We’ve seen the videos and read the articles about many of these activist groups from Green Peace to Extinction Rebellion. We’re just fed up with the fear mongering, the hateful rhetoric, hypocrisy, and acting like Jesus is coming back any moment.

    1. Are you aware that they are actually mostly right?
      The hole in the ozone layer was a huge problem with a lot of alarmism around it. But because of that, things were done to cut back on ozone depleting agents, and the hole in the ozone layer has recovered almost completely.
      The acid rain thing? Huge reason for alarm, huge protests. As you could read in the article here, you know that because things were done about it, the acid rain and other effects associated with it, got significantly less.

      There are many more examples like this, such as asbestos, lead in fuel and paint, catalytic converters and all such things that were once reason for alarm, but now are much less of an issue. Almost like the problems just didn’t exist.

      But those problems *did* exist. We just solved them, to a bigger or smaller degree, because people did something about it. The fact that today it seems like they aren’t a problem does not mean that they never were an actual life threathening issue.

      1. You might not mean the hole has recovered, but has shrunk?

        Anyway, yes, catalytic convertors, spewing out particles of platinum as they degrade, causing an epidemic of asthma in UK cities…

  7. The Earth has not experienced any perceptible warming outside of normal and expected variability and what changes there are are not uniform or stable enough to make any claim along the lines of “The Earth is…”. The Earth is self regulating on a mass-energy scale that is so vast that it makes human activities irrelevant. If the Earth warms, the mass shift from water phase changes causes tectonic effects which in turn releases more sulphur from volcanoes which cools the planet back down again. This suggestion that humans really matter at those scales is egotistical hubris from upstart hairless monkeys.

      1. Not so Kenny, the glaciologists tell me one thing and the geologists and volcanologists tell me another, so when you merge the compatible parts of the different sets of science “facts” that is what you get, a system that self regulates. Have you ever read a paper then looked up the author and had a discussion with them about the implications of their work and how it relates to others outside of their field? Try it some time, I make a habit of it.

    1. The science would really beg to differ.
      IN the shorter term that animation really visualizes the pretty damming evidence, and longer term there is plenty of evidence of a rather more rapid change than any time in remotely recent history bar the ‘act of god’ dino extinction level natural disasters and this is much more sustained – those single point events are very dramatic and show up well in the ice core data for instance, but are also very short lived decaying away in short order. Very much unlike the Industrial revolution…

      There has been enough evidence in the some of the more historically targeted studies as well, that show how things like the black death had a noticeable correlation, and that is a population that went from peanuts by todays standard to barely a city full by today’s standards in the whole of Europe, somehow creating a detectable impact and that’s all without the magic of a million electronic distractions eating lots of extra energy, just the cooking and heat…

      Just how much warming/cooling might be happening right now naturally is debatable, that in barely more than 100 years we have buggered up a previously very much more stable system isn’t anymore – the only debate there is how badly have we shot ourselves, just missing a toe? or is this already into amputate the leg to perhaps, with luck save the patient territory?

      Its far from just egotistical hubris, take the humble beaver for instance just a few of those reintroduced build their damn and end up holding back so much water that the entire area, miles away from them is changed by their presence – and humans are by far the biggest offenders at altering the landscape. In the UK for instance we have basically no land that is actually wild and unchanged by humans. If you then try to work out our impact on the oceans, which with how little we understand them is challenging, it could be fair to claim that maybe at a push you can find a few % of the Earth’s surface that hasn’t be buggered with by humans to some extent, and with microplastics turning up in the artic circle etc perhaps fair to say NOWHERE on the surface of our blue green rock is actually safe from us…

      1. It is a shame that you didn’t read what I wrote more carefully, you did not address the actual points I made, the choice of words matters. IMHO you just proved my point about ego’s, in this case attached to a belief system so firmly that you can’t actually see what is in front of you and parse it objectively.

        1. Oh I read it, and your claiming the Earth is so large that billions of giant hairless apes completely rejigging pretty much the entire surface, turning huge quantities of stuff safely buried for eons into atmospheric gasses in but the blink of an eye is irrelevant is the laughable bit. We throw up more eons old safely buried in the geology stuff as gasses and water pollution than the average volcanic eruption, probably daily and certainly in not a huge period of time… Volcano no matter how biased towards more the system becomes are slow, they can’t outcompete us..

          When its clear in the evidence that even a paltry number of humans by todays standards dying has a real effect of the global climate conditions its rather hard to claim ‘oh we are irrelevant as the Earth is so massive’ now there are soo soo many times more people, and they consume so very much more per captia… That was a total global population of something like 500million dropping perhaps 100-200million and its a noticeable change! Now the population is in the billions…

          The only thing that the Earth 100% certainly is going to be is orbiting the sun for a prolonged period, the state of it’s biome isn’t in any way certain to be or ever return to liveable – as once the system is broken life, at least as we know it just can’t function in the new environment, and life is a large part of the biome regulation. Perhaps you noticed that we are not dinosaur and the world is very very different now to then? And that mass extinction event is potentially a small fry change to what we are doing to ourselves, as so far we don’t show any signs of really changing our ways or dying off to the changes…

          1. You didn’t address the points I made at all, instead you launched into obvious lies. “completely rejigging pretty much the entire surface” Hmmm and when was the last time you got any respect from adults for that sort of irrational hyperbole? I have no nice word to describe you. Go and waste somebody else’s time, unless you have some actual science to discuss?

          2. Find areas of the Earths surface free from micro plastics, or other oil products like soot that shouldn’t be there, that hasn’t been touched at all by the artificially generated acidic rains, etc… I mean there are giant garbage patches full of plastics in the oceans, to go with all the fertilizer and pollution we are pumping out that despite the huge volumes of the oceans is changing the chemistry of the water…

            Not to mention that since the invention of agriculture a very long time ago now the natural world has be very very heavily modified by the humans that live there to suit them, and now humans live and farm nearly all the land area on this rock… Back when our population was small finding trees several hundred years old was trivial and larger ‘fields’ challenging, now in large parts of the world both are the exception not the rule.

            We really have altered the natural state of the entire surface to some extent, and over a rather substantial portion of the land area we have even poured heaps of tarmac and concrete to be about as far from natural as possible, might only be around 1% of the Earths total surface area, but as that surface is 3/4 ocean…

            The more you look the more you find that humanities impacts can be directly seen and measured even in places humans mostly are not – like the bloody Arctic and the middle of the oceans.

            The Science really doesn’t point to a system that ‘self-regulates’ in the way we would commonly mean it geologically! As that would imply its actually got a real consistent norm to return to, which we have ample evidence it doesn’t. Or the world would return to as it was during the Dinos after recovering from the wobble that wiped them out, or would never have changed from how it was before them etc. Life makes up a huge amount of the ‘self-regulation’ of the system, but life is rather more fragile than geological process and we are driving more and more species to extinction, altering ecosystems on massive scales – in short pushing change well beyond the living part of the climate regulations ability to adapt to and deal with!

            If you mean ‘self regulation’ as in the temperature range possible is within a very very large window absolutely, largely dictated by our distance to the sun as there is only so much energy being put in, with a little regulation around whatever atmosphere the geological processes can create…

  8. Climate Models Of Incompetence
    By Dr. Duane Theresher – 6 Feb 2019


    NCAR is a premier climate modeling institution in the world with one of the most famous climate models, which at the time was called the Community Climate Model (CCM).

    My code is still in CCM (or whatever warm fuzzy new name they yet again gave it). It even has my name on it; look at the code here and search for Thresher (and note that they even misspelled my first name once).

    Climate scientists are not programmers. I’m unique in that respect. Climate scientists also don’t want to do the hard work — taking courses and getting degrees — to become programmers. UA/NCAR was my epiphany that climate scientists’ IT incompetence was destroying climate science.

    After my M.S. from UA/NCAR, I fled to Columbia University and NASA GISS (Goddard Institute for Space Studies), in New York City, for a Ph.D.

    I thought that going to a famous private university like Columbia and a famous organization like NASA would improve the climate modeling situation. I could not have been more wrong; it made it worse, much worse.

  9. Sadly from what I see in the USA and Europe we are not going to cut emissions sufficiently to stop significant climate change. We all expect someone else to do it and we are not prepared to give up the things we have got used to. The real understanding of what has to happen to save the planet as we know it today is very low in 98% of the population. Suspect we will bumble on not delivering on the promises the politicians make until we get into major trouble. (they don’t understand the science and the real actions will get them kicked out of power) At this point the only solution will be Climate engineering. We consider it an unknown risk today, in the future it will become the lesser of 2 evils. Bottom line is we need to try harder to really reduce our CO2 (understanding the difference between trivia and real changes would be a good start) but also try and understand what we can do in the upper atmosphere to reflect more heat. Suspect this will not happen until 70% of the earth is becoming very hard to live in.

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