Too Much Uncertainty To Act
May 4th, 2009Posted by: Roger Pielke, Jr.
Soot (sometimes called “black carbon”) has been widely identified as an important climate forcing, with recent research (e.g., here and here in PDF) suggesting that soot emissions have played a potentially “very large” role in warming of the Arctic. Here is how the New York Times recently characterized the role of soot in climate change:
While carbon dioxide may be the No. 1 contributor to rising global temperatures, scientists say, black carbon has emerged as an important No. 2, with recent studies estimating that it is responsible for 18 percent of the planet’s warming, compared with 40 percent for carbon dioxide. Decreasing black carbon emissions would be a relatively cheap way to significantly rein in global warming — especially in the short term, climate experts say. Replacing primitive cooking stoves with modern versions that emit far less soot could provide a much-needed stopgap, while nations struggle with the more difficult task of enacting programs and developing technologies to curb carbon dioxide emissions from fossil fuels.
In fact, reducing black carbon is one of a number of relatively quick and simple climate fixes using existing technologies — often called “low hanging fruit” — that scientists say should be plucked immediately to avert the worst projected consequences of global warming. “It is clear to any person who cares about climate change that this will have a huge impact on the global environment,” said Dr. Ramanathan, a professor of climate science at the Scripps Institute of Oceanography . . .
So it is with some surprise that the EPA has decided that the science of soot in the climate system is too uncertain to act. Courtesy of Environmental Capital here is what the EPA endangerment finding says about the role of soot in the climate system:
Like other aerosols, black carbon can also affect the reflectivity and lifetime of clouds. How black carbon and other aerosols, such as sulfates, alter cloud properties is a key source of uncertainty in quantifying the total human influence on the global climate. This total cloud indirect effect caused by all aerosols (e.g., sulfates, black carbon and organic carbon) is estimated to be causing a net cooling effect, with a large range of uncertainty. Given these reasons, there is considerably more uncertainty associated with black carbon’s warming effect compared to the estimated warming effect of the six long-lived greenhouse gases.
In other words, unlike carbon dioxide, soot does not qualify as a pollutant with respect to climate change due to what EPA calls “considerably more uncertainty” in the science. Really? I’m not sure how this would be assessed, but the role of soot in the climate system has been extensively studied.
Despite EPA’s judgment that the science is too uncertain to act, an interesting group of policy makers has decided otherwise:
Sens. Tom Carper (D-Del), Jim Inhofe (R-Okla.), Barbara Boxer (D-Calif.) and John Kerry (D-Mass.) introduced legislation directing the U.S. Environmental Protection Agency (EPA) to study the environmental impact of black carbon and the most cost-effective ways to reduce its emissions to improve public health and reduce global warming.
So if the science is robust and the political will is there, why would EPA steer away from black carbon as an “easy win” on climate change? Here is my guess:
EPA seems to have painted itself into a corner with its endangerment finding. If black carbon is a pollutant due to its role in global and regional climate change, then as a precedent it opens up the door to a lot of uncomfortable questions and potential actions. For instance, if black carbon is an important forcing that affects the climate system with negative impacts, then why not water vapor emissions from land use, which also has been shown to influence local and regional climates? What about other land use change that alters surface energy budgets, such as albedo changes, irrigation, urbanization, and land clearing? And so on. Black carbon is an inconvenient forcing, and thus for EPA, rather than open up a can of worms, they have decided to follow the tried and true approach of hiding behind uncertainty.
May 4th, 2009 at 7:12 am
An Inconvenient Forcing? Sounds like a book – call your agent quick!
May 4th, 2009 at 8:07 am
Black carbon 18%. CO2 40%. Really?!
It is hubris of the worst kind to publish such exact numbers on the pitifully weak scientific evidence available. For an intelligent policy maker, this should be a red flag. Warning — Serious absence of wisdom ahead.
May 4th, 2009 at 8:41 am
I agree with Stan that the use of such precise numbers is a demonstration of hubris. Reminds me of the old saw, “42.7% of all statistics are made up on the spot”.
But I am curious about the 40% figure. Can anyone tell me where they got that? Is that a commonly accepted number in AGW circles?
May 4th, 2009 at 8:46 am
What is interesting to me about this discussion is the question of scientific uncertainty, and attemtping to understandi exactly what the components are of that uncertainty so that different uncertainties can be compared across topic areas.
For example, GCM models have uncertainties and their associated downscaling efforts have even more uncertainties – how do these uncertainties compare with soot uncertainties? Are they 20% less certain or 500% more certain? Or are these “certainties” really a heuristic composite of values with unspecified weights? And if there are unspecified values in these judgments of overall “uncertain science”, should these be compared with the costs of dealing with the uncertain outcomes to make a good policy decision?
Should we have panels of scientists (interdisciplinary) determine (based on some consistent approach) the estimated uncertainty for a given scientific claim prior to its use in policy?
May 4th, 2009 at 9:46 am
But I am curious about the 40% figure. Can anyone tell me where they got that? Is that a commonly accepted number in AGW circles?
It’s probably from something like Figure SPM.2:
http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-spm.pdf
However, CO2 in that figure is slightly larger than all the other positive forcings combined (even solar forcing). So I don’t know how they got a number as low as 40%.
May 4th, 2009 at 10:24 am
The trouble with that black carbon research, which i used to believe in, is that it all predates the recent rapid recovery of the Arctic ice:
http://nsidc.org/data/seaice_index/images/daily_images/N_timeseries.png
The slowdown of the Chinese economy perhaps? We’ll just need to wait and see. Looks to me that this fruit is rotten though.
May 4th, 2009 at 11:13 am
jasg,
The 2007 meltback could have been caused, in part, by an accumulation of BC on the surface of the ice over many years. If this hypothesis has merit it suggests that the 2007 meltback should be followed by a ice recovery since the BC would have been washed away with the ice. The BC would then continue to accumlate and trigger another 2007 like event in 5-10 years.
May 4th, 2009 at 11:23 am
“The trouble with that black carbon research, which i used to believe in, is that it all predates the recent rapid recovery of the Arctic ice:
http://nsidc.org/data/seaice_index/images/daily_images/N_timeseries.png
The slowdown of the Chinese economy perhaps? We’ll just need to wait and see. Looks to me that this fruit is rotten though.”
The Chinese slowdown (producing less black carbon) may have something to do with it. But a certain factor is that we are emerging from sunless winter. The primary effect of black carbon is on the albedo of the Arctic. Because there is no sunlight in winter, the black carbon effect is negated, thus the rapid recovery each of the last two winters.
A demonstration is here: http://climatesci.org/2008/04/02/guest-weblog-on-albedo-from-mike-smith/
Mike
May 4th, 2009 at 11:29 am
[...] Roger Pielke Jr., wonders: So if the science is robust and the political will is there, why would EPA steer away from black [...]
May 4th, 2009 at 11:49 am
Come on, folks, you all know that the EPA decided, a priori, for political reasons, to regulate CO2, regardless of any silly scientific considerations . They will get to soot, all in good time, if it suits their political objectives. Sorry to be so cynical, but I just can’t help it.
May 4th, 2009 at 1:04 pm
I think Roger may be jumping the gun in his conclusions here. What evidence do we have that the EPA has made its decision about black carbon on political, rather than scientific grounds? I glanced at the two “recent research” links, and and although there are discussions and estimations of the aerosol indirect effect (AIE), it’s not clear to me how accurate or justified the assumptions are. If these authors’ methods have proven that their AIE estimates are much better than what anyone, including the IPCC, has estimated before, its not clear to me from these publications, and anyway, although I’m not a climate scientist, I would expect such a result to reach very high-profile journals and be loudly trumpeted. Maybe I missed it, but I haven’t seen it yet.
The aerosol indirect effect, or cloud albedo effect, or whatever you want to call it, is a major area of climate uncertainty, and black carbon is much more likely to modulate this effect than CO2 or other long-lived greenhouse gases.
And aside from the two research papers, why rely on the NYT for technical information?
So, while I find Roger’s theory ascribing a political motive to the EPA’s black carbon plausible, I am not convinced its necessarily true by the evidence presented.
May 5th, 2009 at 2:36 am
Raven
Doesn’t new snow cover up old carbon thus negating its albedo-changing properties?
Mike Smith
Winter happens every year. This year something has changed, which coincides with 2 years of planetary coolness.
I’d say the jury is still out.
May 5th, 2009 at 7:32 am
Of course, soot is actually TOXIC. But I guess the EPA doesn’t need to worry about things like that.
May 5th, 2009 at 9:13 am
jasg,
Not necessarily. Light penetrates into the snow.
More importantly, when the snow/ices melts the previously covered BC will be exposed and increase the melt rate. But once the snow/ice complete melts the BC is lost into the ocean.