I had been under the impression that aerosols had a cooling effect.  My knowledge if this is largely non-scientific (in college, I remember a great ski season being attributed to the eruption of Mt. Pinatubo).  But I think the "nuclear winter" possibility highlighted during the cold war was based in large part on the volume of dust that would be kicked up by a nuclear strike (see: Pinatubo),and I vaguely recall reading that declining particulate emissions have accelerated AGW.  

Can some more scientifically literate Grist readers educate me on why particulate cools but soot heats?  (Or correct my shoddy scientific memory?)

The suggestion that Congress take note is predicated upon the assumption that Congress is concerned about the public welfare rather than special interests.

BAU = Business As Usual
AAE = Above All Else

Aerosol is both associated with radiative warming and cooling, a complex mix. Aerosol (or particulate in the 1.5 and 10 micron diameter sizes) is comprised of:

black carbon (BC), associated with burning of fossil fuels - which can absorb sunlight and warm

organic carbon (OC), also associated with burning of fossil fuels and condensation of gases - also know as "white carbon" that reflects light and therefore cools (very short-lived)

sulfate (SO4), formed via heating of fuel sulfur and secondary ionic reactions - volcanoes often form tremendous sulfate plumes causing shading and cooling

minerals and metals, such as Saharan dust, also associated with shading and cooling

For most industrial burners, sulfur is removed with scrubbers and coarse particulate such as minerals and some BS are removed by electrostatic preciptitators.  Ultra-fine aerosol is left, mostly secondary BS, trace mercury, etc.  Scientists can measure BS on polar ice shields and not a profound influence on warming there.

It should be noted that the Number 1 Greenhouse gas is water vapor.  Rain cannot form without a particle nucleus. Interesting stuff.

Onward through the fog

Ramanathan's Scripps Institute (UC SAN DIEGO) team first announced their results back in August 2007 to a mostly disinterested media. It was, however, immediately received by climate skeptics as an indicator that the IPCC's proclamations were overwrought and premature. Ramanathan's team wasn't looking to exculpate CO2 however, they were investigating the more general disruptive climate changing effects of the notorious Asian Brown Cloud (aerosols (sulfates, soot) in a continuation of their IPCC-sponsored INDOEX study.

At the time Ramanathan stated that the net heating effect within mid-tropospheric brown clouds were contributing a net heating effect - not a net shading effect. Instead of the two components canceling out each other's effects, soot's net heating effect exceeds that of its shading effect and the higher reflectivity of sulfates. One factor may be that the hotter rising clouds of soot segregate themselves away from the whiter, cooler sulfates where their effect is enhanced and self-propelling.

The general effects of aerosol-ladened brown clouds had already been observed to disrupt the formation of low-level rain clouds, actually reducing both regional cloud-top albedo (reflective heat-rejecting cloud tops) as well as surface-cooling shading from rain clouds.

In August 2006, however, Ramanathan's team took their field data and applied them to climate models. Not only were high-level brown clouds found culpable for HALF of regional warming anomalies formerly blamed on CO2 but the brown clouds were generally responsible for 40 percent of the warming over the vast Pacific (30 percent of the Earth's surface).

What has added grist to the counter-mill of so-called climate skeptics is that Ramanathan's team was making direct observations in situ, running sorties of small robotic planes at various altitudes sampling atmospheric chemistry and temperature - the significance being that direct empirical data apparently contradicted many climate models as well as the public proclamations of the IPCC and pro-environment politicians. For once the climate skeptics had a real chink in the empirical armor of climatology and global politics. All the other speculations on the effects of solar activity, dyssynchrony in the Vostok paleo ice samples, etc., were piffle compared to the Scripps Inst. team's discovery.

The significance of this discovery shouldn't be understated, however, because it still turns the world's attention to both sustainable development and international cooperation. The bulk of global soot pollution is still from itinerant farmers working the land via slash and burn farming as well as fueling their cook stoves with wood. This isn't to blame the itinerant poor but to consider what the industrialized West can do to help them replace their use of wood as cook fuel and subsidize better agricultural methods. The answer, paradoxically, may be to encourage them to use petroleum-based cooking fuels and fertilizers (made from natural gas), bio-char black carbon and other soil amendments.

For that to be feasible, however, methane, kerosene and gasoline prices will need to become more economical to itinerant farmers through both subsidies and sustained conservation efforts (fuel efficiencies & energy use cutbacks). This again turns the focus on the industrialized nations to mitigate their petroleum throughput.

As Ramanathan famously stated, this does seem to provide a way out of a very broad conundrum, because the results of soot abatement are immediate realized - as opposed to the 15 - 25 year atmospheric half life of methane or the 40 - 50 year half life of atmospheric CO2.

The results will also provide other positive synergistic results: Deforestation near temperate and tropical glaciers has decimated the microclimate recharge effect of forests acting as an atmospheric watershed. Likewise the mid-tropospheric air-borne soot strata directly sully and heat both temperate and tropical glacial packs (in the Himalayas, in the American Rockies and famously on Kilimanjaro). Mitigating the use of arboreal cook fuels and itinerant slash-and-burn agriculture will both mitigate climate change and help reclaim now-vanishing glacial watersheds. Likewise flooding problems in low-lying areas like Bangladesh largely stem from upstream deforestation that results in worsening watershed flooding downstream.

Likewise we can foresee another benefit of soot-reduction being the reclamation of Arctic and sub-Arctic glaciers as well as tundra conditions (a potential source of methane under run-away thaw conditions). The Arctic has suffered terribly from the snow-darkening heating effects of soot deposition - up to 25 percent of the past century's warming can be attributed to the Arctic melt-off, and up to 90 percent of that has been due to soot. Due to the nature of westerly winds, most of the current soot deposition in the Arctic is borne from S.E. Asia, along with a fair amount from Russian oil fields and the rest from industrialized N. American and Europe.

I hope that helps.

--leebert

That helps a great deal indeed. Many thanks.

grist.org

Do the simpler stuff first that has lower cost and higher gain.  Maybe such a near-term focus can include:

capturing soot, including disseminating & requiring cleaner diesel engines

reducing fugitive methane emissions by plugging leaks in natural gas infrastructure plus capturing & burning the methane from landfills

 preserving old-growth forests as carbon offsets as well as planting new forest

(preservation needs to be paired w/ planting a like area of new forests in order to really have integrity.  otherwise it counts something you DIDN'T do as being a gain.  

Conversely, ONLY counting new tree plantings ignores other areas being deforested that offset that gain.  so to really count as a valid carbon reduction credit, there has to be both old AND new forest areas protected w/ single unit of carbon credit -- essentially doubling the amount of carbon sequestered in trees over the emissions they offset)

I know this is a bit more controversial, but the Scripps team's discovery does lend credence to the counter-claims that current CO2 levels are in fact nearing the asymptotic (reverse logarithmic) saturation point whereby atmospheric CO2 contributes increasingly marginal warming in the atmosphere.

Manifold water vapor feedback effects have been modeled to reflect the observed warming of the past century. But these global models were lacking the Ramanathan team data on soot's net effects and were admittedly tailored to model CO2 as the main causative agent of observed temperature anomalies( warming). Again, this doesn't exculpate CO2, but perhaps we are closer to CO2-driven AGW leveling off (as critics like MIT's Richard Lindzen have suggested). CO2 won't be exculpated but if modeled CO2-driven water vapor feedback loops (based on absorption spectra transfer) aren't as big a culprit as once thought, then we might be due for a small sigh of relief. There's still plenty of work ahead, but the options may have broadened.

Perhaps the next field studies may focus on soot's heat absorption transfer characteristics in conjunction with water vapor as well. Perhaps soot's role is even more insidious in humid air than dry (c.f., its observed effects over the Indian & Pacific Oceans), further softening the fears of CO2's synergistic warming effects in conjunction w/ water vapor. Only further research will tell.

Does this announcement pokes a hole in the idea of consensus? Here's Ramanathan - as solid and stolid a climatologist as we have - and his little robot planes may have done more to drive a hole through the IPCC's claim of scientific consensus than the American Enterprise Institute could have hoped to accomplish with years of agitprop and shoddy science. It also takes air out of the "climate denier" industry that has already back peddled from completely rejecting that there has been any change in global temperatures to bickering over potential causes of global warming. Perhaps this will help ease the debate so the world can consider our options.

A compounding factor may be the current minimum in solar sun spots. Sun spot activity has been declining for the past 3 - 4 years and has almost bottomed out in the past 5 months (conditions for short wave radio operators who rely on an activated ionosphere have been quite poor). Is this downtrend in sunspot activity only a decadal minimum or is this a broader trend on the order of the bicentennial minima (like those that been correlated longer-term cooling spells like the Elizabethan Mini Ice Age). Apparently the cooler sun slows down oceanic air currents such that continental land masses are a great deal colder in the winters. This could actually exacerbate our problems because societies in the temperate latitudes will consume more combustible products (coal, fuel wood, etc.) emitting both more CO2 & soot to warm their homes, etc.

Just as controversially I don't think either China or India can be exempted from any future climate change protocols. The recent findings that China's emissions per unit of production are 40 percent higher than the global average seems to undermine the claims of Kyoto advocates that her per capita emissions are a third of the West's. Likewise China's stack-top soot emissions are visibly the worst in the world, but even with previous citations against its vast brown clouds China has claimed entitlement to leniency. It's bad enough the West has been exporting jobs to the East but then we're being asked to increase emissions as well? How this jibes with progressive ideals is beyond me: Screw domestic labor and the global environment. Oh, and civil rights in China. I can't agree to paying the Chinese communists to continue on with Business As Usual - if we're supposed to change our habits, they better themselves. A nascent boycott against Chinese goods is already in its third year....

China's functional exemption from Kyoto was was, after all, the reason why the US Congress voted to reject Kyoto (as did Clinton, Gore & Bush after them). The USA isn't the sole Kyoto holdout then - it has a recalcitrant - almost belligerent - Chinese communist oligarchy as company. No more, methinks - this is a truly global problem and the Chinese government owes many areas needing redress, namely Tibetan autonomy, human rights and the environment. There are a lot of cards on the table, Taiwan in the mix, so it seems high time for more Sino-American detente.

Onward through the fog....

Good to hear somebody with an appreciation of the subject of aerosols. I would be hesitant to say that black carbon (also black soot or BS, sometimes elemental carbon or EC) takes away anything from the CO2 pathways.

But I was surprised that when our company applied for contracts to measure transportation releases of particulate aerosols for several large federal agencies, all the bids were pulled and none were funded. Whaaaaaaat?

The way of the future for diesel transportation is low sulfur fuels for less sulfate and particulate filters [and similar technologies] for the exhausts - by 2014 we'll be seeing many on the road and used off-road in the US.

When I was on an EPA committee regarding emissions inventories for fine particulate one of the fascinating studies was done to show that many small, prescribed fires used to thin forests were much better than uncontrolled wildfires. Geogenic and biogenic aerosol continues to be a large problem in any country.

Then here's one for the Gristers. Bio-aerosols from cattle, hog, and other CAFO's not only carry some nasties, but some of the most potent and drug resistant diseases we know. Mid-West Research, Texas A&M, and EPA-Research Triangle Park did a bunch of work on that. Stay away from those boogers - and those partly treated wastewater systems for golf courses ain't too dang healthy either!

If anything gets swept up into the transport layer above 30 meters it can go a long, long way.  /sam

Onward through the fog

  If in fact BS is a significant unmodeled driver, that would mean that the climate sensitivity to a perturbation of the radiative energy balance is a bit lower than currently assumed. It does not mean that the logarithmic dependency of the importance of CO2 is refuted, the direct effect of a given amount of CO2 on the thermal balance is well known. It is only how sensitive the climate is (degrees of heating per watt/meter**2) of additional heating that is difficult to determine. We have used a combination of data (paleoclimate studies, and recent response to things like Mt Pinatubo, and modeling) to pin down that sensitivity. A somewhat lower sensitivity would only somewhat lesson the need for emissions reductions.

There ya go. One hypothesis is that global dimming due to dust, smoke, and smokestack pollution has masked that CO2 could really do to global temperatures, if that effect was absent (global dimming). Another camp says that black soot (BS, whatever) can be transient yet very powerful because it is emitted in such great amounts by man-made sources such as industry and transportation.  

Glacial and large ice forms provide many of the answers, since they not only record the aerosol deposition (including BS) but also the atmospheric gases when the ice was formed, such as by using drilled core samples.  

One of there very, very strange ideas I have heard is that is industry and transportation were cleaned up to 90% aerosol reductions, including the Chinese power plants, massive changes in the atmosphere could happen very quickly. What those would be are only a source of speculation.  

Onward through the fog