Attribution the hard way: black carbon soot

I’m on a quest–not for retribution but for attribution. The climate is warming and there are several factors pushing temperatures upward, as well as several others pushing back in resistance, trying to keep temperatures down. I really want to know how much each factor contributes to our effects on climate. I am having trouble finding specific numbers for each factor, so it’s going to take time–sorry to drag you all through this with me.

The common unit of measure for climatic forcing agents is the energy perturbation that they introduce into the climate system, measured in units of watts per square meter (W/m2).

According to the IPCC AR4…

  • The combined radiative forcing due to increases in carbon dioxide, methane, and nitrous oxide is +2.30 [+2.07 to +2.53] W m–2, and its rate of increase during the industrial era is very likely to have been unprecedented in more than 10,000 years (see Figures SPM.1 and SPM.2). The carbon dioxide radiative forcing increased by 20% from 1995 to 2005, the largest change for any decade in at least the last 200 years. {2.3, 6.4}
  • Anthropogenic contributions to aerosols (primarily sulphate, organic carbon, black carbon, nitrate and dust) together produce a cooling effect, with a total direct radiative forcing of –0.5 [–0.9 to –0.1] W m–2 and an indirect cloud albedo forcing of –0.7 [–1.8 to –0.3] W m–2. These forcings are now better understood than at the time of the TAR due to improvedin situ, satellite and ground-based measurements and more comprehensive modelling, but remain the dominant uncertainty in radiative forcing. Aerosols also influence cloud lifetime and precipitation. {2.4, 2.9, 7.5}
  • Significant anthropogenic contributions to radiative forcing come from several other sources. Tropospheric ozone changes due to emissions of ozone-forming chemicals (nitrogen oxides, carbon monoxide, and hydrocarbons) contribute +0.35 [+0.25 to +0.65] W m–2. The direct radiative forcing due to changes in halocarbons[8] is +0.34 [+0.31 to +0.37] W m–2. Changes in surface albedo, due to land cover changes and deposition of black carbon aerosols on snow, exert respective forcings of –0.2 [–0.4 to 0.0] and +0.1 [0.0 to +0.2] W m–2. Additional terms smaller than ±0.1 W m–2 are shown in Figure SPM.2. {2.3, 2.5, 7.2}

Today I’m interested in black carbon, also known as black soot or, just for the sake of variety, black carbon soot. You see above that the IPCC combined it with aerosols and other particulate matter and assigned the group a total forcing of -0.7 watts per square meter.

However, in 2013 a team of scientists 232-page report in the Journal of Geophysical Research. They estimate the radiative forcing of 1.1 watts per square meter. An article in Environment 360 from Yale University made the obvious point:  “If black carbon is responsible for trapping so much heat, then reducing soot may be an effective way to slow down the planet’s warming. It’s even more attractive because black carbon washes quickly out of the atmosphere, and so reducing soot emissions would lead to a fast fall in the concentration of black carbon in the atmosphere. Carbon dioxide, by contrast, lingers for centuries in the atmosphere.” Hence the focus on removing black carbon by the Fast Mitigation crowd, including me–and James Hansen, who came up with a similar forcing figure in a paper he co-authored with Makiko Sato (“Global atmospheric black carbon inferred from AERONET”).

The figure is net–black carbon heats when it’s in the atmosphere, but there are also cooling effects associated with it, not to mention its role in reducing the albedo of snow covered ground when it turns white into grey. But 1 watt per square meter is the end result of counting all that, far greater than the IPCC estimated.

If black carbon produces more than a third of the radiative forcing of greenhouse gases, and if it is true that black carbon is much easier to abate than gases, the Fast Mitigation posse should be making their point more strongly. If coupled with reductions in other areas, such as short-lived climate pollutants (SLCPs) – including methane, black carbon, tropospheric ozone or hydrofluorocarbons, the claim is that we could reduce temperatures (all else being equal) by 0.5C by 2050. If we then make progress on deforestation, renewable sources of energy and large scale substitution of coal-fired energy plants, we’ve actually got something going on.

This is why attribution is key to a climate strategy. Activists claim that efforts to reduce other climate forcing agents are at best misguided, at worst evile strategies promoted by fossil fuel fanatics determined to sell their coal and oil.

But if climate change really is the challenge of the millenium, we will probably need more than one weapon with which to combat it. To rely on something as iffy and complicated as reducing CO2 emissions when it is possible to bring other forces to bear as well (not instead)… is daft. Silly. It’s like…

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8 responses to “Attribution the hard way: black carbon soot

  1. I want to repeat my previous comment: the NET energy imbalance is about 0.5 to 0.6 watts per m2. This figure can be estimated by taking the ocean energy content change from 0 to 700 meters, and dividing by the earth’s surface area.

    If your figures turn out to be right, all we have to do is 1. reduce forest burning, and emissions from diesel and coal; plus 2. Reduce methane emissions from oil and gas facilities, rice paddies, and cattle.

    This can be achieved by some regulatory changes, some research, and a bit of money. But I’m not sure if the powers that be are interested in something practical.

    You know, I’ve been reading CIA analyst and field agent books, and based on what they can reveal, a large fraction of the USA intelligence community feels the USA and Europe have to achieve energy independence from the Saudi-Emirates-Kuwait Sunni alliance, as well as the Iran-Iraq-Syria Shiite combine. This requires a significant shift away from oil. So maybe the “irrational” behavior we observe isn’t really about global warming?

    • Fernando,

      You wrote: “all we have to do is 1. reduce forest burning, and emissions from diesel and coal; plus 2. Reduce methane emissions from oil and gas facilities, rice paddies, and cattle.”

      By “reduce forest burning” do mean stopping poor subsistence farmers from using slash and burn agriculture?

      “emissions from diesel and coal” Do you mean other than CO2? That would be particulates, which cause a net cooling.

      “Reduce methane emissions from oil and gas facilities” I think that is relatively minor compared to agriculture. And producers already have an economic incentive to do that.

      “rice paddies” How do you do that without banning rice production.

      ” and cattle.” That would require banning beef and dairy production.

      These proposals are completely impractical. Also, taking these would only produce a temporary reduction in forcing that would then start to rise again due to CO2 emissions.

      • I will try to answer these points in more detail by tomorrow. But there are rice varieties which have lower methane emissions.

        Since I’m a petroleum engineer I can confirm a well crafted regulatory regime can cut methane emissions. And I’ve seen operators who don’t chase vented gas properly. I even had operating field personnel venting gas in operations I supervised, and had to get very hard nosed to stop them.

        Simply put, the effort is worthwhile but it requires a bit of awareness and focus mention operators lack. State owned oil compañies are terrible in this área.

      • Fernando,

        “State owned oil compañies are terrible in this área.”
        I can believe that, so there is indeed probably some low hanging fruit there. Natural gas is about 20% of total methane emissions; cutting that by 75% would reduce forcing by about 0.1 W/m^2. That is maybe 3 years of CO2 emissions.

        “there are rice varieties which have lower methane emissions.”
        It is not the rice that emits the methane, but the paddy (essentially an artificial wetland). So I suppose this means dry land rice. That does exist, but I am sure there are good reasons why it is not cultivated in most areas.

  2. I have always been amazed by street scenes in China with carts stacked high with coal briquettes for heating and cooking.

  3. Tom,
    Great essay. It deserves to be discussed widely. You have pointed out one of the many opportunity costs the CO2 obsession has imposed on us: Carbon black is *solvable*. Coal can be burned cleaner. Natural gas burns with basically zero soot. Diesel and maritime bunkers oil can be utilized more cleanly and their carbon black can be reduced. But instead we have the climatocracy and their endless false predictions of doom as they jet set from conference to conference. And the massive waste of windmills. Not to mention the real way to reduce carbon black: Nuclear power.
    .

  4. Tom,

    If black carbon forcing really is as large as 1.0 W/m^2, then climate sensitivity is below the lowest end of the IPCC ranges. I say this because analysis of observational data, by Nic Lewis and by others, indicates a climate sensitivity near the bottom of the IPCC range (1.0 to 1.5 K for TCR, 1.5 to 2.0 K for ECS). But those use conventional forcing estimates. A large soot forcing would raise the total forcing by 40% or more; that would produce a 30% or more reduction in sensitivity.

    p.s. – Why are you using AR4 instead of AR5?

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