CO2 emission reductions can do no more than reduce the rate of increase of CO2 concentrations. As warming increases and understanding grows, groups not aligned with green ideologies will increasingly call for action. Among them, at least, any plausible technological fix will likely gain advocates. And indeed there is a technological fix -- the sunscreen fix -- that can quickly and inexpensively cool the Earth. This fix is more than plausible, I expect it to get a lot of attention.
The sunscreen fix is this: Replicate the cooling effect of natural volcanic eruptions by adding sulfur dioxide (SO2) to the stratosphere. The quantity required would be several percent of total human SO2 emissions. An SO2 sunscreen can't fix all the problems caused by excess CO2. Just the global warming problem.
I urge that we examine this concept with open minds and then consider whether to urge that others do so as well. Whether we do this or not, the stratospheric sunscreen fix is, I think, on its way to becoming a live option. The reasons for this are presented (rather timidly) by Paul Crutzen, a Dutch scientist who won the Nobel prize for discovering the chemistry of ozone depletion. Once again, he is telling us something about the stratosphere, human choices, and the fate of the world. Let's listen.
His article in Climate Change, August 2006, can be gotten here:
And here is the journal's only slightly confused press-release:
The potential human and ecological benefits of a fix for global warming are reason enough to take this seriously. And considering the political prospects, dare we not? As I describe below, a toxic political dynamic has already begun, a dynamic that positions environmentalists and their allies to be discredited in an area where they now hope to find their greatest strength.
I have set out the positive case for the sunscreen fix below in part to show what it sounds like. Documentation of various points can be provided on request. First, some background --
1. Reducing CO2 emissions will not reverse warming
If CO2 emissions stopped completely, near-current CO2 levels would persist for decades. If emissions stopped increasing today, CO2 levels would continue to increase at roughly present rates. But with China and India industrializing, even this dramatic achievement -- holding emissions constant -- would merely stop the acceleration of the rise in CO2 levels. And let's not forget the positive-feedback loops: melting ice darkens arctic waters, growing vegetation darkens arctic land, warming tundra emits CO2, and so on. As we know from Earth's history of rapid climate change, this process creates enormous risks.
In short: even with the application of political will far beyond what we've seen, a policy limited to reducing CO2 emissions would let the Earth slide deeper and faster into global warming, with unpredictable and possibly disastrous consequence.
2. Nature has shown us that an SO2 sunscreen can reverse warming
From time to time, explosive volcanic eruptions put millions of tons of SO2 into the stratosphere. SO2 stays in the stratosphere for 2 year or so in the form of microscopic sulfate particles. These scatter sunlight, making sunsets redder, the sky slightly whiter, and the Earth a bit cooler. This happened most recently after June, 1991, when Mt. Pinatubo exploded in the Philippines. This placed about 10 million tons of sulfur into the stratosphere and cooled the Earth by about 0.5°C in 1992. According to many climate models, 0.5°C corresponds to several decades of greenhouse warming. The cooling effect can be scaled up: In August, 1883, Mt. Krakatoa exploded in Indonesia; this lowered global temperatures by about 1.2°C in 1884. In 1815, Mt. Tambora exploded in Java; 1816 is known as "the year without a summer" -- there were snowstorms in New England in June. Applying the sunscreen fix would provide a temperature control that can be adjusted over a wide range.
3. Creating an SO2 sunscreen appears to be low-harm and low-risk
Volcanic eruptions are natural experiments that show the effects of adding SO2 to the stratosphere, and modeling can tell a lot about how these effects would operate if sustained. It's a safe bet that, with experience and modeling, there wouldn't be big surprises. Also, the effects would take years to create, because it would take years to build the capacity to make and lift the required millions of tons of SO2. This would give time to observe and judge the effects, which would anyway fade away in a few years if the program were stopped.
The effect on ozone concentrations was shown by the Pinatubo experience: According to Crutzen, who pioneered the chemistry of stratospheric ozone depletion, the global effect was negative but small (2.5%), less than the loss after Pinatubo. This is similar in magnitude to year-to-year variability and is about 10% of typical seasonal variability. For perspective, in the famous southern-hemisphere ozone hole, the loss has been in the range of 40 to 70%. (Nonetheless, the magnitude and distribution of ozone depletion strikes me as one of the more important uncertain effects.)
Adding SO2 to the stratosphere would later increase the precipitation of SO2. The increase, however, would be a few percent of current human SO2 emissions (which total about 80 million tons per year). Since human SO2 emissions have recently been decreasing by a few percent per year, maintaining an SO2 sunscreen in the stratosphere would do no more than temporarily slow the decline of SO2 in the lower atmosphere. The SO2 sunscreen fix would add a small amount of a natural substance to the environment. By reasonable standards, it can be considered clean.
The overall risks and adverse effects seem comparatively small and uncertainties will shrink as models are refined and the historical data are studied. If the comparison is made not to some ideal standard of zero adverse effects and absolute certainty, but instead to the enormous effects and sickening uncertainties of ongoing warming, the relative risks seem clear.
4. The sunscreen fix would be relatively inexpensive
Crutzen estimates that 5.3 million tons (5.3 billion kg) of sulfur per year would offset the warming effect of doubling atmospheric CO2; something like 2 million tons per year would offset CO2 levels projected for 2050. Sulfur production could be increased by this much at a cost around 0.1 $/kg (mining operations of similar scale and cost were shut down 30 years ago because of falling prices). Regarding the cost of delivery to the stratosphere, Crutzen cites a 1992 estimate of 25 $/kg, but the of delivery using jet aircraft should be less than 5 $/kg, even with fuel costs based on oil at 150 $/barrel -- some ways of doing the job would burn no fuel at all. (For comparison, the airfreight industry worldwide carries about 30 million tons of cargo per year, earning revenue of about $60 billion.) A generous estimate of the total annual cost would be about $10 billion, about 1/5000 of the current gross world product.
5. Pollution cleanup has been removing sunscreen
In the journal Climate Change, Crutzen summarizes recent discoveries regarding low-altitude atmospheric particulates, including SO2-derived sulfates:
...the warming of earth by the increasing concentrations of CO2 and other greenhouse gases is partially countered by some backscattering to space of solar radiation by the sulfate particles, which act as cloud condensation nuclei....Through acid precipitation and deposition, SO2 and sulfates also cause various kinds of ecological damage. This creates a dilemma for environmental policy makers.
...after earlier rises, global SO2 emissions and thus sulfate loading have been declining at the rate of 2.7% per year, potentially explaining the observed reverse from dimming to brightening in surface solar radiation at many stations worldwide....According to model calculations by Brasseur and Roeckner (2005), complete improvement in air quality could lead to a decadal global average surface air temperature increase by 0.8 K on most continents and 4 K in the Arctic. Further studies by Andreae et al. (2005) and Stainforth et al. (2005) indicate that global average climate warming during this century may even surpass the highest values in the projected IPCC global warming range of 1.4 - 5.8°C. [emphasis added]
In short, cleaning up SO2 in the lower atmosphere is increasing warming, but adding smaller amounts of SO2 to the stratosphere could compensate. The stratospheric sunscreen fix could be viewed as a prudent way to offset an unintended consequence of cleaning up the air we breathe.
6. The main problem with the sunscreen option?
The sunscreen option will, of course, undermine efforts to reduce CO2 emissions, and CO2 emissions have effects other than warming. For one, increasing CO2 lowers ocean pH, with unknown but possibly enormous ecological effects. For another, although screening sunlight can reduce global mean temperature, the geographic distribution of heat input and loss would still change, hence some degree and kind of climate change would still occur. Adding an SO2 sunscreen isn't equivalent to reducing CO2 levels, but it can keep the polar ice caps from melting.
(By the way, I've ignored other sunscreen options here, such as using carbon particles instead of SO2. Crutzen expects that these would be ozone-neutral, and perhaps positive.)
Looking toward future decades, it may well be that improvements in production technologies will make emission-free energy sources inexpensive enough that reducing emissions will become easy. If so, then a moderate degree of political pressure at that time will accomplish more than major political mobilization could accomplish today. The more attractive the energy alternatives, the less the resistance to change. An partial solution today will not preclude a more complete solution later.
Still, there is a natural impulse to oppose any development that lessens public motivation to address the root problem. This is an instance of the familiar political logic of wanting a situation grow worse in order to force change. Trying to make things worse, however, tends to make one unpopular.
7. A toxic political dynamic has begun
I had planned to explain why I expect anti-green forces to embrace the fix as a "solution", while green forces feel threatened by the promise of positive climatic effects, oppose the proposal for that reason, and get politically clobbered. I then found that this toxic political dynamic has already begun, saving me the effort of explaining. Here are excerpts from an article on the Heartland Institute website:
Nobel Laureate Offers a Solution to Global Warming
Nobel Prize-winning scientist Paul Crutzen, professor emeritus at Utrecht University in the Netherlands, has set the scientific community afire with a proposal to address global warming, should it be demonstrated to endanger the planet....
"This whole issue is a reasonable subject of debate," said Patrick Michaels, professor of natural resources at Virginia Tech University and past president of the American Association of State Climatologists.
..."The technology exists to engineer the planet's climate to our liking, and the subject will increasingly be discussed in public and scientific circles because people who look at the data know that there is very little that can be done to alter the temperature trajectory of the planet merely by curtailing carbon dioxide emissions with present technology."
...Nevertheless, the Independent reported Crutzen's proposed atmospheric insurance policy "is so controversial that some scientists opposed its publication in the peer-reviewed scientific press, fearing that it may encourage the view that it is easier to treat the symptoms rather than the causes of climate change."
"That's a pretty naked admission that what is scientifically true and credible is being repressed, for political purposes, by ideologues," observed Michaels. "This is not the way science is supposed to operate. Such behavior speaks for itself regarding how so many alarmists are willing and indeed eager to throw truth under the locomotive wheels of political advocacy." [emphasis added]
In the press release for his paper, Crutzen is quoted:
"Given the grossly disappointing international political response to the required greenhouse gas emissions,...research on the feasibility and environmental consequences of climate engineering of the kind presented in this paper, which might need to be deployed in future, should not be tabooed...the possibility of the albedo enhancement scheme should not be used to justify inadequate climate policies but merely to create a possibility to combat potentially drastic climate heating." [emphasis added]
Consider the scale of attention that global warming should be getting today, and may get in the near future. Imagine that the green/progressive end of the political spectrum backs to CO2 reduction positioned in opposition to SO2 cooling. Now, imagine the dynamic illustrated above, but scaled up to match the true magnitude of the issue. Imagine the policy debates... the talking points... the "balanced" news stories... the full consequences of defending a policy that ensures accelerating climate change, and doing so for what will be seen as politically manipulative reasons.... Not a pretty picture. And not even good for the polar bears.
The policies generally advocated to mitigate climate change are -- with respect to global temperature -- ineffective in comparison to the sunshade fix. It would be hard to argue that the fix is worse than the problem without appearing to advocate global warming. If the facts are as they seem at the moment, then to stand in opposition would be objectively harmful and politically disastrous.
If CO2 and projected global warming are important, then SO2 and potential global cooling are equally important. It is time to consider a newly emerging option with an open mind.
That's the basic story as I understand it. I was relatively indifferent until I started looking into this last week, and perhaps I am being hasty.
A postscript for the introspective:
If the sunscreen concept disgusts you, please ask yourself why. Then, please formulate reasons that you can articulate. Finally, please consider whether you can state those reasons in a way that would make sense to a family on the Bangladeshi flood plains, or to voters who watch talking heads on television in Ohio. Here is your audience: