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.

How Much Warmer?

If the present global temperature trend continues for the remainder of the year, we're bound to hear a growing chorus of reports about 2010 being the warmest year since records have been kept. The first six months of 2010 already appear to have been the warmest first half on record. Or was it? When you examine the numerical result from the National Climatic Data Center upon which this determination rests, it turns out that January-June of this year apparently topped the previous six-month record set in 1998 by just 0.03°F. Not only is that difference quite small, but there's a good chance it doesn't exist at all and is merely the result of average temperature data being tallied to more decimal places than the accuracy of the instruments recording them warrants. So when someone tells you this is the warmest year ever, you should at least ask for more detail on that assertion.

Before going any further let me clarify that this point doesn't affect the validity of climate change. When I look at the accumulating evidence, including the climate data that's publicly available, I see a decade-by-decade warming trend since the turn of the previous century, with a few time-outs. It's open to debate whether that trend is currently in abeyance; neither the incidence of a couple of relatively-cooler years recently--giving rise to claims of global cooling that at a minimum must be regarded as highly premature--nor a single hotter year this year necessarily alters that, at this point. However, there are good reasons why media-hyped claims about any one year being warmer or colder than another are pretty much irrelevant to the larger discussion concerning climate change. And in at least the current instance they likely rest on a foundation that simply can't bear their weight.

The global annual temperatures we see reported are really averages of the averages of numerous temperature readings from thousands of weather stations around the world. Such averaged data can only be as accurate as the least-accurate individual readings on which they are based. This reflects a principle called "significant figures" or "significant digits" that is drummed into students of college chemistry and physics. (If you're interested in the details, the USGS has a good overview here.) So if you take three temperatures, say 59.1°F, 56.3° and 58.7°, their average is not 58.03333° (as my calculator tells me), or even 58.03°, in the manner that most of the climate data centers report such figures, but simply 58.0°. Furthermore, if you take the difference of two such averages, that difference can't create greater accuracy than the individual readings. For example, if I subtract from the above figure the global average temperature of 57.2°F for the period 1951-1980 used by NASA's Goddard Institute for Space Studies (GISS), the result is not 0.83333° or 0.83°, but 0.8°.

Applying this common-sense principle becomes even more important when you take into account the actual accuracy and precision (repeatability) of the underlying measurements. A quick Google search turned up a 2004 paper in the Journal of Atmospheric and Oceanic Technology on this subject. After analyzing several sources of measurement error in commonly-used air temperature sensors, the authors found that these devices were accurate to no more than +/-0.2°C over a typical range of temperatures, and less accurate beyond that. So not only are the temperature readings that go into the averages upon which comparisons of global annual temperatures are based only good to one decimal place, but they may not be quite that good. Even if some of this error averages out over the large number of observations recorded (assuming it is random error), we still shouldn't read more into these data than is there, and the second of the two digits in the "temperature anomalies" (differences vs. an agreed average) that are reported should probably only be used to ensure that rounding is done consistently.

What does all this mean in practice? Well, referring to the GISS data it appears the global average temperatures for 1998, 2002, 2005, 2007 and 2009 were all essentially indistinguishable from each other at 14.6°C or 58.3°F. 2010 might be on track to beat that by a full 0.1°C, though it could still easily end up in a tie with these other years. Whether this year sets a new record or not is of little consequence to the climate change discussion. Although not likely to compete with such a finding for headlines, it's much more relevant, important and accurate that the average of temperatures in the 2000s was apparently 0.2°C warmer than the average of the 1990s, which were already 0.1°C warmer than the 1980s, and so on.

Shaken Consensus?

Since the publication of the hacked emails from the University of East Anglia's Climate Research Unit (CRU) last November, we've been inundated with news reports and opinion pieces questioning the scientific consensus behind climate change. An editorial in today's Wall St. Journal on "The Continuing Climate Meltdown" is just the latest example of this trend, following a weekend that saw the release of a remarkable BBC interview with the CRU's former director. The fact that all this coincides with a northern hemisphere winter that has deposited record snowfalls on regions that don't normally see much of the white stuff serves to reinforce the message that something is amiss with global warming theory. It has also had me wondering if I moved far enough south, as I cope with "ice dams", cabin fever, and other consequences of a pair of back-to-back blizzards in the D.C. area. While I agree that the recent revelations have given rise to an understandable wave of doubts regarding climate change, this may say more about the way that extreme climate predictions have been played up in the last several years than it does about actual climate change.

Even the most ardent adherents of the view that climate change is real, man-made to a significant extent, and extremely challenging for humanity must agree that the science supporting this perspective has had a rough couple of months--largely deserved. Whatever the "Climategate" emails said about the underlying analytical rigor of the dominant scientific interpretation of global warming, they revealed a worrying degree of defensive groupthink and gatekeeping among leading climate researchers. I'm pleased to see that an independent group has been set up to examine the practices at East Anglia-CRU, though the inquiry has already experienced controversies of its own.

Meanwhile the Intergovernmental Panel on Climate Change (IPCC), of Nobel Peace Prize fame, is under fire for incorporating unwarranted claims in its reports, including a shockingly sloppy assertion about the rate at which glaciers are disappearing. This has exposed a process that in some instances gave magazine articles and unpublished papers the same credence as peer-reviewed scientific papers in recognized journals. For all the vitriol I see directed against "climate skeptics", the climate change community should accept that these are mainly self-inflicted wounds, and that much of the current public doubt about climate change stems from the unraveling of exaggerated predictions that were expounded without a clear, accompanying explanation of the associated caveats and uncertainties, possibly to promote quicker action by governments.

In contrast, the BBC's interview with Dr. Jones is full of nuances and caveats--though hardly outright retractions, as some have characterized his remarks. I was particularly interested in his comments on the Medieval Warm Period. Although he appears not to have "told the BBC that the world may well have been warmer during medieval times than it is now," he did seem to suggest that we simply don't have sufficient data to determine whether the warming that led to the settlement of Greenland by the Vikings and the cultivation of wine grapes in England was confined to the northern hemisphere or global in extent. Instead of prompting an assumption it wasn't global, this gap in our knowledge ought to galvanize the urgent gathering and correlation of paleoclimate data--samples of the kinds of proxies used to assess temperatures before instruments to measure them (or people to read the instruments) existed. That's because this isn't a quibble over some esoteric bit of history, but a crucial gauge of just how unprecedented the warming of the past several decades has been.

Then there's the temperature data itself. Although Dr. Jones concurred that global warming since 1995 has just missed being statistically significant, the data from the CRU and similar data from NASA do show that on average the last decade was warmer than the 1990s, which were in turn warmer than the 1980s. Despite all the talk of global cooling, the last two years still easily make the top 10 list for warmest years of the last century, and global temperatures currently average about 0.8 °F warmer than in the 1970s. But that doesn't mean that there aren't problems here, as well. Dr. Jones referred the BBC to a map of the weather stations providing the global temperature data compiled by the UK's Met Office (the national weather service) and processed by the CRU. It reveals such measurements to be very dense in the developed countries of the temperate zones and quite thin on the ground--or sea--in the tropics and the high latitudes that account for much of the earth's surface. And even the historical temperature data for the US are still subject to significant revisions, as I noticed yesterday when I rechecked the comparison between 1998 and 1934 than I wrote about several years ago.

So where does this leave us? From my perspective it requires us to think about the definition of a successful scientific theory as one that provides the best explanation for the evidence we see--even if that evidence is incomplete, as seems to be the case here. The fact that some scientists seem to have behaved badly or that others--mostly non-scientists--have promoted alarming-but-uncertain predictions as proven and now have egg on their faces doesn't alter the fact that "anthropogenic global warming" (AGW) based on greenhouse gas emissions still seems to explain more of what we observe going on than any other theory at this point. Hypotheses such as the one attributing warming to the influence of cosmic rays on cloud formation must go through a great deal more vetting before supplanting AGW.

While considerable progress has been made in the last decade solidifying the evidence supporting the AGW theory, significant uncertainty still remains about the future consequences it suggests, particularly as relates to regional impacts and changes in precipitation. A lot more also needs to be done to clarify the relationship between proxy data and instrumental temperature data, and to ensure that the latter are consistent and truly representative. However, I don't see these deficiencies as justifying complete policy paralysis, particularly when it comes to those actions that can be accomplished relatively cheaply, such as improved energy efficiency, or that offer substantial benefits for other concerns such as energy security, including expanding nuclear power, low-cost renewable energy, and R&D to bring down the cost of other renewables. As for whether the time is right to pursue more comprehensive measures, there's a legitimate debate to be had, but it shouldn't start from the false assumption that anthropogenic global warming has been disproved.

Cooler Is Relative

Well, it's official; the average global temperature for 2008 was 14.44° C (57.99° F.) That's 0.13° C (0.23° F) cooler than 2007's 14.57° (58.23° F.) In fact, according to NASA's Goddard Institute for Space Studies (GISS), 2008 was the coolest year since 2000. However, it was also the 9th warmest year since at least 1880, and warmer than any year on record prior to the mid-1990s. The average temperature for the current decade is running 0.2° C warmer than the decade of the 1990s, and 0.3° C warmer than the 1980s. Being as objective as possible, I have a hard time interpreting last year's slight dip as providing much support for the notions of "global cooling" that I began noticing on the Internet a year ago. That's a pity, considering last week's sobering report from the National Oceanic and Atmospheric Administration (NOAA) on the likely duration of the effects of global warming on the climate, even after we eventually get greenhouse gas emissions under control.

As I noted in my posting on the subject last February, the global cooling hypothesis rests not just on the observed slight decline of average temperatures since the peak year of 2005--including a sharp monthly drop last January, compared to January 2007--but also on concerns about tardy sunspots and the recent decline in solar output. NASA's graph of "solar irradiance", the energy in sunlight reaching the earth's orbit, confirms that the sun's activity is at a periodic low point within the approximately 11-year sunspot cycle. It also indicates that this cyclical low is somewhat lower than recent lows, and that it seems a bit overdue for a cyclical uptick. (To put this in perspective, we are currently receiving about 0.02% less solar energy than average.) However, unless the scientists at a recent conference on solar activity were wrong in concluding that were are not headed into a sustained solar minimum of the kind associated with the Little Ice Age, then the implications of this graph and of GISS's commentary on solar irradiance look ominous in the other direction: We could be in for some sharply warmer temperatures in the next decade, a few years after sunspot cycle #24 reaches its peak, when the "non-negligible effect on global temperature" of variability in solar irradiance would reinforce, rather than partially canceling out the effects of greenhouse warming and the Southern Oscillation (El Nino/La Nina.) As a result, my money is still on warming, not cooling.

That makes the NOAA findings worrisome, even if one doesn't expect to be around to see whether their assessment that the adverse consequences of global warming could persist for as long as 1,000 years after our emissions have completely ceased proves correct. On a more personally-relevant timescale, however, it suggests that we shouldn't expect the climate to return smoothly to the previous "normal" after we stop nudging it, whenever that might be. That kind of systemic irreversibility is distinct from the idea that plant and animal species that become extinct along the way won't be retrievable; it speaks to the basic hospitableness of the earth to the levels of human population we're asking it to carry. (If you think that sounds extreme, you should read James Lovelock's recent thoughts on the subject.)

If the aim of policy makers is to create a sufficiently robust public consensus to support a cap on carbon emissions and a big investment in low-carbon energy over the span of time necessary for them to have the desired results, then their explanation of the problem must encompass the variability inherent in the interaction between greenhouse gas emissions and the complex cycles and systems that governed the climate long before the first factory began burning coal, or the first Model T was built. "Global warming" implies a steadier process than we are likely to experience. Some years will be cooler than others, as we've just seen, but the decade-by-decade trend still points higher. Our growing understanding of the consequences of that ought to make this harder to shrug off, even if we assign it a probability lower than 100%. I don't know if we'll end up burying biomass-derived charcoal as Mr. Lovelock suggests, in order to suck CO2 out of the atmosphere, but the longer we delay action, the more dramatic the options we may be forced to consider.

Allergic to Climate Change

An item on the ABC World News the other night linking allergies and climate change caught my attention. It referred to a paper in the current issue of The Journal of Allergy and Clinical Immunology describing a connection between climate change and increased levels of pollen production, and thus higher expected incidences of asthma and other allergic maladies. Although the focus of the article was mainly on the future consequences of continued global warming and other environmental impacts, it also looked at changes that are already evident today. That's the angle ABC picked up on, tying the study's findings to a particularly bad allergy season that millions of Americans are experiencing. The key message: if you suffer from pollen allergies, climate change will very likely make them worse--perhaps a lot worse.

Compared with more dramatic outcomes such as droughts, heat waves, rising sea levels, and increased numbers of highly-destructive hurricanes, a bit of hay fever doesn't sound so bad. Having been plagued by allergies for my entire life, I'm not sure I'd agree with that assessment. For many of the one in five Americans who suffer seasonal allergies, it's an important quality of life issue, and for the 20 million afflicted with asthma, this is potentially life-threatening. It's also an anticipated consequence of climate change that could affect people who live far from any coastline or hurricane-affected areas and might otherwise only notice that it's getting a bit warmer. And although hay fever remedies have improved, the good ones are not cheap and still have side effects, while the permanent cure, immunotherapy, requires a significant commitment of time and can trigger some unpleasant allergic reactions along the way.

The mechanisms underlying the study's finding of increased seasonal allergies are pretty simple. Higher atmospheric CO2 levels cause vegetation to grow faster and larger--though apparently not to the degree previously thought. Unfortunately, that also seems to apply to plants like ragweed, resulting in bigger weeds emitting more pollen. Now throw in warming average temperatures, bringing earlier spring-like conditions and longer growing seasons. Whatever that combination might do for crop productivity, we should also expect to apply to less desirable plants and their pollen counts.

While that prospect merits concern, it's also important to understand the limitations of this study. A glance at its contents reveals that it was not a clinical report on allergy patients over time, but rather a literature search on the mechanisms of climate change, plant biology, and allergic and asthmatic responses to various allergens. It draws many of its assumptions about the expected course of climate change from the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, of Nobel Peace Prize-sharing fame. That won't satisfy all critics, but we ought to be relieved that the four MDs who authored the paper didn't attempt to reinvent climate theory for themselves.

I'm well aware from the comments I receive that my readers are not uniformly worried about climate change. Some remain skeptical of the evidence for human responsibility, and a few doubt we are even warming in any discernible way, or think the globe might now be cooling. But whether you buy the whole enchilada, or only part of it, it's worth considering that climate change is beginning to alter our world in ways large and small, predictable and surprising, and that even if it doesn't drown all our coastal cities and dry up our crops, it could still make the earth into a much less hospitable place than the environment that enabled our ancestors to move beyond hunting & gathering, build cities and civilizations, and expand our population a thousandfold. More severe allergies aren't the worst alteration we can imagine, but this looks like yet another factor to which we and our descendants must adapt, if we don't get our emissions under control.

Warming or Cooling?

As if the politics of addressing global climate change weren't already daunting enough, a new paper published in Nature this week suggests that the Northern Hemisphere, where most of humanity lives, could be due for a cooling trend, thanks to shifting ocean currents. Coming at a time when the idea of global cooling has been making the rounds on the internet, the prospect of a break in the observable warming trend greatly complicates the task of policy makers who are answerable to their electorates. It would be much harder to contemplate jarring changes to the economy to reduce greenhouse gas emissions, if the polar ice were to stop retreating and glaciers stabilized, or even began to grow again.

The new prediction is based on modeling work described in today's New York Times. It also prompts comparisons to predictions that global warming might trigger even more dramatic cooling, by altering the strength and path of the Atlantic thermohaline current, or "salt conveyor". Once again, we are reminded that global warming has always been a highly imprecise term for the complex processes now at work. That's why I prefer "climate change"--not as a euphemism, but as a more accurate description of the outcomes we face. Some even prefer "global weirding."

But while environmentalists may embrace this new scientific view of climate change as more volatile than the steady warming many have expected, climate skeptics will see it as a glaring inconsistency, particularly if the global rise in temperature stalls. That matters because it seems unlikely that the public's growing worries about climate change result from having absorbed the scientific consensus embodied in the reports of the Intergovernmental Panel on Climate Change (IPCC), rather than from media coverage of melting icecaps, shrinking glaciers, unusual heat waves and droughts, and the other evidence that fits a pattern of warming. If the visible evidence began seriously to diverge from that trend, I am skeptical that faith in science would sustain the public concern that must underpin any serious regulatory efforts, whether we're talking about emissions cap and trade, a carbon tax, or even the milder sector-specific targets that the President recently proposed.

Those who approach climate change with a quasi-religious fervor are likely to become apoplectic at any suggestion that a few cooler months or years might derail the growing policy momentum to institute the means of dramatically reducing emissions. But while they might be comfortable dismissing out of hand a winter that was 0.5 degrees Celsius colder than the previous one--punctuated by a sharp rebound in March--the rest of us might prefer a polite and practical conversation about how such variability could still be consistent with the overall trendline. Ultimately, our understanding of climate change must always remain incomplete, and so we must remain flexible enough to incorporate the new knowledge we will inevitably turn up along the way. Isn't that the essence of science?

The Path to Zero

An article in today’s Washington Post reported on new scientific research suggesting that emissions of greenhouse gases must be reduced to zero by mid-century, in order to prevent global warming that could persist for hundreds of years, perhaps eventually producing average temperatures higher than for millions of years. As the climate debate focuses increasingly on policy, the impact of such findings on efforts to craft practical frameworks for reducing US and global emissions becomes as important as the scientific result itself. The implication of the need for truly radical change contained in this latest report might either galvanize action on capping our emissions, or convince us that none of the current pathways for reducing emissions is truly worth pursuing.

The goalpost for stabilizing the climate has been moving for some time. A few years ago, moderating emissions to stabilize the atmospheric CO2 concentration at about twice its pre-industrial 280 parts per million (ppm) was widely regarded as adequate to the task. Further modeling suggested that 550 ppm wouldn’t do the trick, but that 450 ppm might. Then we heard from NASA’s James Hansen that we need to shoot for 350 ppm, a level we unfortunately exceeded in the late 1980s. Now Matthews and Caldeira’s paper in Geophysical Research Letters indicates that if we wish to avoid continued, dramatic climate change over the very long haul, our real goal must be zero net emissions, with as rapid a return as possible to pre-industrial levels. It’s enough to make you throw up your hands in futility.

I don’t think you need to be an economist or a climate skeptic to appreciate just how sweeping the changes in our entire global economy would have to be, in order to achieve zero emissions worldwide by mid-century. Of the current US cap-and-trade proposals, neither the bill now before the Congress nor the proposals of any presidential candidate would get us close to that. Even if the EU and US cut emissions by 80%, the toughest target now on the table, global emissions will continue to grow for at least several more decades and would probably still be above 50% of current levels in 2050.

What does zero emissions mean in practical terms? Well, among other things it doesn’t mean “zero emission vehicles” that merely shift the point of emissions from the tailpipe to the smokestack. And while it’s possible to imagine getting a large part of the way toward a 70% or 80% emissions reduction through greatly-improved efficiency and conservation, we simply can’t conserve our way to zero. Instead, it implies the elimination of essentially all combustion of fuels, other than in facilities that capture and sequester all the CO2 they produce, or of biofuels that absorb in cultivation as much CO2 as they emit when processed and burned. Otherwise, we’re talking about an entirely electrical world, with power generated exclusively by wind, solar, geothermal, hydro, and nuclear sources. Those sources currently meet only 14% of the world's energy needs. For those of us grounded in the realities of fleet, capital stock and infrastructure turnover, the cost associated with changes on such a scale makes adaptation to a warmer world seem like the more attractive option.

As overwhelming as all this seems, however, I see two positive nuggets embedded in this report. One is the timescale for reductions and the other is the notion of zero net emissions. Fifty years is a long enough interval in which to develop entirely new technologies from fundamental scientific discoveries, fine tune them, and roll them out on a massive scale. If we can at least stop making the problem bigger in the meantime, the actual means of reducing our emissions to zero might emerge from an unexpected quarter within the next decade, or from a novel application of some existing technology. And with enough cheap, clean energy at our disposal—perhaps from space solar power—we could even reduce our net emissions below zero, by extracting CO2 from the air and storing it in geological formations or as carbonate rock.

At this point, I believe we ought to be cautious about this new finding. Even ignoring the possibility that the authors’ modeling results won’t hold up, pushing a complete zero-emission agenda now, before we’ve even begun reducing global emissions, seems premature. Combine the implications of zero emissions with the new debate about “global cooling”, and we could have the recipe for another decade of policy gridlock. In the meantime, however, we should be pondering what this research suggests about the proper balance between incremental change and transformation, where the latter is a realistic option. That might seem like a highly esoteric topic in the current economic climate, but in the years ahead climate policy and the economy will likely be increasingly inter-connected.