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Solar Warming and Our Sulfur Sunshield

Two unrelated stories concerning the science of climate change caught my attention yesterday. The first was the announcement of a new report on solar variability, published in Nature, which appeared to upend established thinking about the impact of solar cycles on the earth’s climate. The other was a discussion on Shell’s climate blog of the potential impact of regulations affecting the sulfur content of marine fuel oil on an effect that has been partly mitigating climate change for decades. Both are interesting in their own right, while together providing a useful reminder that climate change is much more complex than the soundbites we typically hear from the media and advocacy groups, especially after we’ve had a run of unusually hot or cold weather.

As a less-than-fully reformed science nerd, I loved the simple elegance of the first sentence of the abstract of the Haigh, et al paper in Nature: “The thermal structure and composition of the atmosphere is determined fundamentally by the incoming solar irradiance.” Paragraphs of exposition boiled down to 16 words that neatly frame the importance of the researchers’ finding that for the last several years, and contrary to what we’d have expected from being in the low part of the solar cycle, featuring few or no sunspots for several years, the earth has been receiving more energy from the sun where it really counts–in the lower part of the atmosphere, or troposphere. If their interpretation of the satellite data is correct, then it pretty well torpedoes the notion from two years ago that a weak sun was about to flip global warming into global cooling. Of course it would also defuse some of the determined attempts to attribute this year’s record temperatures entirely to humanity’s greenhouse gas emissions.

While this finding isn’t expected to alter the decade-to-decade view of climate change, it certainly suggests that we should be paying attention to a lot more than just CO2 and its sibling GHGs over shorter intervals, and in that respect it’s a nice lead-in to the discussion of atmospheric cooling due to sulfur emissions from ships. That also applies to its implication that we still have a lot more to learn about the earth’s atmosphere–where climate lives–and its dynamic interaction with the solar system.

In his blog on Shell’s corporate website, Shell climate advisor David Hone shared his observations from a recent meeting exploring the impact of sulfur emissions on climate change. This apparently led to discussions of sulfur-based strategies for geoengineering the climate, but even without going that far it seems clear that this issue deserves a lot more attention that it has received. I was aware that such emissions tend to offset at least part of our greenhouse gas emissions, and that previous reductions in sulfur for onshore fuels–necessary for local air quality and modern vehicle anti-pollution equipment–might have given an unintended boost to warming. However, I think this is the first time I’ve seen the estimated climate forcing associated with marine fuels of –0.6 W/m2, which as Mr. Hone notes is not small relative to the total greenhouse gas forcing of around 2 W/m2. This situation surely justifies a serious re-think of the International Maritime Organization’s decision to slash the sulfur content of all marine fuel burned globally, particularly since it is hardly the only alternative available to address the negative effects of these emissions on most human populations. It’s also a much more expensive option for shippers–and thus anyone who benefits from international trade–than confining the low-sulfur rules to coastal waters. According to the analysis cited by Mr. Hone, the latter scenario would preserve nearly 80% of our sulfur sunshade, while the global low-sulfur rule would more than halve it.

When I was involved in marine fuel supply and distribution on the West Coast early in my career, it was already clear that the emissions from burning high-sulfur bunker fuel were a major source of pollution in port cities and coastal areas, and that the importance of addressing them would grow once most onshore emission sources, from power plants, trains and other mobile sources had been dealt with. Some of the sulfur was eliminated as large marine diesel engines replaced the old steam turbines, and much of the rest was addressed with restrictions on the quality of fuel that could be burned in port and along the coast. For now, vessel owners can comply with these rules by carrying two different fuels: enough of the more expensive low-sulfur fuel for use in US and other regulated coastal waters, and the rest consisting of much cheaper high-sulfur fuel for use on the high seas. That approach, which would no longer be an option after 2020 under the IMO rules, cleans up the air where it matters most but still puts enough SO2 into the atmosphere to scatter some of the incoming solar energy and offset part of the warming from CO2.

Using one form of pollution to offset another is hardly a perfect solution, but just as many scientists and environmentalists urge caution about introducing new geoengineering measures before we understand their consequences well enough, we should think long and hard about tampering with this long-standing, if inadvertent geoengineering process until we have something better in mind to replace it, or until we no longer need it.

Geoffrey Styles's picture

Thank Geoffrey for the Post!

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David Lewis's picture
David Lewis on Oct 14, 2010 5:04 am GMT

Joanna Haigh, lead author of the solar study, is quoted on the NatureNews website, starting four paragraphs up from the end:

“The findings could prove very significant when it comes to understanding, and quantifying, natural climate fluctuations,” he says. “But no matter how you look at it, the Sun’s influence on current climate change is at best a small natural add-on to man-made greenhouse warming.”

“All the evidence is that the vast majority of warming is anthropogenic,” agrees Lockwood. “It might be that the solar part isn’t quite working the way we thought it would, but it is certainly not a seismic rupture of the science.”

Regarding your second point, what you are talking about, basically, is that we are already faced with decisions some thought would only come up if we were talking geoengineering.  I.e. geoengineering is already in progress. 

Now that we understand that some anthropogenic emissions (GHG) are warming the planet, and some may be cooling the planet (anthropogenic aerosols) if we act to change what we are doing with the idea of limiting climate change we are engaged in geoengineering. 

The main problem with aerosols, which tropospheric sulphur is just one,  is what effect they have is so poorly understood. There doesn’t seem to be confidence about the magnitude and even the sign of some of them and there is great uncertainty about the overall effect.

Eg, according to Atmospheric Aerosol Properties and Climate Impacts, put out by the US Climate Change Science Program:

“The IPCC AR4 (2007) concluded that uncertainties associated with changes in Earth’s radiation budget due to anthropogenic aerosols are the largest contribution to the overall uncertainty in radiative forcing of climate change among the factors assessed over the industrial period”

What Hansen points out in his talks is that he thinks many would agree that it is almost as likely that the total effect of aerosols could be twice as powerful a cooling forcing than what the IPCC has agreed to say is their most likely scenario, in other words, since it is possible that emissions of anthropogenic aerosols will be reduced in future, as Hone is dicussing in his blog, and given that if emissions are reduced they disappear from the atmosphere in a matter of weeks, (compare to CO2: centuries) this is a time bomb awareness of which makes GHG control even more urgent.

Schellnhuber writes that the odds for avoiding what is looking to be almost certain disastrous global warming might be “improved by aerosol management”

Reuters was reporting that the EPA is about to tighten dust standards farmers will have to meet under the terms of the Clean Air Act.  No one quoted or written about in the report, i.e. the NRDC, the farmers, the EPA, or the politicians, seemed to understand that there are climate implications to modifying what we do in the way of emitting aerosols.

Hence it is a valid point to wonder if controlling aerosols is worth putting resources into as opposed to controlling GHG. After reading Hone’s blog post I wondered if they had anyone at the conference he is speaking of who understood how serious ocean acidification is.  At least they understood that geoengineering with aerosol, whether in the stratosphere or troposphere, does nothing to counter what is happening to the oceans. 

Nothing is going to make sense in terms of global climate strategy until it is generally agreed that there is a problem, i.e. anthropogenic emissions causing climage disruption, to be solved. 

Geoffrey Styles's picture
Geoffrey Styles on Oct 14, 2010 3:45 pm GMT

David,

Thanks for your very detailed and thoughtful response.  “Now that we understand that some anthropogenic emissions (GHG) are warming the planet, and some may be cooling the planet (anthropogenic aerosols) if we act to change what we are doing with the idea of limiting climate change we are engaged in geoengineering” is very well put.  It’s further complicated by the potential of acidification from sulfur emissions to drive more CO2 out of the oceans and into the atmosphere.

I think what we’re left with is not an either/or proposition in terms of addressing GHGs and the emissions that appear to be counteracting them to some degree, but one of managing the timing of our efforts so as not to make things worse in the process. 

Noel Flantier's picture
Noel Flantier on Oct 14, 2010 4:23 pm GMT

Hansen made a prediction that analysis of the planetary surface temperature would set a new record hgh in 2010,  just when the morons were all trumpeting that the planet was cooling.  He illustrated his reasoning by showing what happens as heat “sloshes” around the Pacific Ocean in El Nino/La Nina events.  Steady winds drive relatively warmer water to build up in a thick layer near Asia, which reaches a maximum, then the heat spreads out over the entire Pacific, cutting off colder water upwelling near Peru, which affects how the chart for the planetary surface temperature appears.  Yearly variation in the planetary surface temperature analysis, especially when it apparently shows that the planet is “cooling”, doesn’t impress anyone who is actually interested in what is going on, as opposed to those interested in delaying doing anything about the stark long term accelerating warming trend. 

David Lewis's picture
David Lewis on Oct 14, 2010 5:06 pm GMT

I hesitate to draw conclusions based on my first contact with a paper such as the one on “acidification from sulphur emissions” your link goes to.  A quick scan of the conclusion seems to indicate that the effect the authors are describing is significant in coastal areas rather than on a global scale.  Eg:  “On a global scale, the alterations in surface water chemistry from anthropogenic nitrogen and sulfur deposition are only a few percent of the ocean acidification and Δ[DIC] increases expected from the oceanic uptake of anthropogenic CO2.”  My local paper (Seattle) reports that oysters are no longer reproducing on this coast and have not been doing so for several years and the cause is not known for certain – this is the kind of thing changes in coastal ocean chemistry can be expected to produce. 

The problem with management strategy is the low or medium low confidence scientists say they have in their estimates for the effect of the various aerosols.  You can look at a number, like -0.6 watts per square meter and think it is as meaningful as +3 watts for GHG but it isn’t.  Scientists have high confidence in the numbers for the various GHGs but they are saying they are not confident about aerosol numbers.  The scientific effort to understand the effects of aerosols needs to be beefed up, meanwhile the forces who want to pretend that climate scientists are criminals or idiots who do junk science seem to be increasing.  You can’t “manage” what you have little understanding of.  It looks likely that people will want to control emissions of some aerosols for other reasons than their effect on climate while opponents of climate action continue to succeed in keeping the US from leading the world into effective global climate action. 

“What we’re left with”, is that the forces driving global climate disruption accelerate every day. 

By the way, do I detect in your phrase “using one form of pollution to offset another is hardly a perfect solution” an admission that CO2 is a pollutant? 

Geoffrey Styles's picture
Geoffrey Styles on Oct 14, 2010 7:09 pm GMT

“an admission that CO2 is a pollutant”

LOL.  My view remains the same: it’s only a pollutant in the sense that harmful excesses of water (flooding or drowning) would be consdiered such. But it had a nicer ring than “one emission to offset another”.   

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