Black carbon

Black carbon or BC is formed through the incomplete combustion of fossil fuels, biofuel, and biomass, and is emitted in both anthropogenic and naturally occurring soot. Black carbon warms the planet by absorbing heat in the atmosphere and by reducing albedo, the ability to reflect sunlight, when deposited on snow and ice. Black carbon stays in the atmosphere for only several days to weeks, whereas CO₂ has an atmospheric lifetime of more than 100 years. [V. Ramanathan and G. Carmichael, "Global and regional climate changes due to black carbon", 1 NATURE GEOSCIENCE 221-22 (23 March 2008) (“The BC forcing of 0.9 W m–2 (with a range of 0.4 to 1.2 W m–2) … is as much as 55% of the CO₂ forcing and is larger than the forcing due to the other GHGs such as CH₄, CFCs, N₂O or tropospheric ozone.”)]

Black carbon contribution to global warming

Black carbon is a potent climate forcing agent, estimated to be the second largest contributor to global warming after carbon dioxide (CO2). Because black carbon remains in the atmosphere only for a few weeks, reducing black carbon emissions may be the fastest means of slowing climate change in the near-term.

Estimates of black carbon’s climate forcing (combining both direct and indirect forcings) vary from the IPCC’s conservative estimate of + 0.3 watts per square meter (W/m2) + 0.25 [IPCC, "Changes in Atmospheric Constituents and in Radiative Forcing", in CLIMATE CHANGE 2007: THE PHYSICAL SCIENCE BASIS. CONTRIBUTION OF WORKING GROUP I TO THE FOURTH ASSESSMENT REPORT OF THE INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE 129, 132 (2007), available at http://www.ipcc.ch/ipccreports/ar4-wg1.htm. (Magnitudes and uncertainties added together, as per standard uncertainty rules)] , to the most recent estimate of 1.0-1.2 W/m2 (see Table 1), which is “as much as 55% of the CO2 forcing and is larger than the forcing due to the other greenhouse gasses (GHGs) such as CH4, CFCs, N2O, or tropospheric ozone.” [V. Ramanathan and G. Carmichael, "Global and regional climate changes due to black carbon", 1 NATURE GEOSCIENCE 221-22 (23 March 2008) (“The BC forcing of 0.9 W m–2 (with a range of 0.4 to 1.2 W m–2) … is as much as 55% of the CO2 forcing and is larger than the forcing due to the other GHGs such as CH4, CFCs, N2O or tropospheric ozone.”)]

In some regions, such as the Himalayas, the impact of black carbon on melting snowpack and glaciers may be equal to that of CO2 ["Id." at 221 and 224] . Black carbon emissions also significantly contribute to Arctic ice-melt, which is critical because “nothing in climate is more aptly described as a ‘tipping point’ than the 0°C boundary that separates frozen from liquid water—the bright, reflective snow and ice from the dark, heat-absorbing ocean.” [Charles Zender, Written Testimony for the Hearing on Black Carbon and Climate Change, U.S. House Committee on Oversight and Government Reform 1 (18 October 2007), available at http://oversight.house.gov/documents/20071018110919.pdf [hereinafter Zender Testimony] . ] Hence, reducing such emissions may be “the most efficient way to mitigate Arctic warming that we know of.” , [Zender Testimony, "Id." at 6 (“Reducing Arctic BC concentrations sooner rather than later is the most efficient way to mitigate Arctic warming that we know of.”). ]

Since 1950, many countries have significantly reduced black carbon emissions especially from fossil fuel sources, primarily to improve public health, and “technology exists for a drastic reduction of fossil fuel related BC” throughout the world [V. Ramanathan, Testimony for the Hearing on Black Carbon and Climate Change, U.S. House Committee on Oversight and Government Reform 4 (18 October 2007), "available at" http://oversight.house.gov/story.asp?ID=1550 [hereinafter Ramanathan Testimony] (The developed nations have reduced their black carbon emissions from fossil fuel sources by a factor of 5 or more.. Thus the technology exists for a drastic reduction of fossil fuel related black carbon); "but compare" Bond, T. C., E. Bhardwaj, R. Dong, R. Jogani, S. Jung, C. Roden, D. G. Streets, and N. M. 'Trautmann Historical emissions of black and organic carbon aerosol from energy-related combustion, 1850–2000", 21 Global Biogeochemical Cycles GB2018 (2007) (Previous work suggests a rapid rise in [global] black carbon emissions between 1950 and 2000; this work supports a more gradual, smooth increase between 1950 and 2000).] .

Reduction of black carbon

In its 2007 report, the IPCC estimated for the first time the direct radiative forcing of black carbon from fossil fuel emissions at + 0.2 W/m2, and the radiative forcing of black carbon through its effect on the surface albedo of snow and ice at an additional + 0.1 W/m2 [IPCC, "Changes in Atmospheric Constituents and in Radiative Forcing", in CLIMATE CHANGE 2007: THE PHYSICAL SCIENCE BASIS. CONTRIBUTION OF WORKING GROUP I TO THE FOURTH ASSESSMENT REPORT OF THE INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE 129, 136, 163 (2007), "available at" http://www.ipcc.ch/ipccreports/ar4-wg1.htm] . More recent studies and public testimony by many of the same scientists cited in the IPCC’s report estimate that emissions from black carbon are the second largest contributor to global warming after carbon dioxide emissions, and that reducing these emissions may be the fastest strategy for slowing climate change ["See id". at 164, 170, 174-76, 217-34 (citing studies by Ramanathan, Jacobson, Zender, Hansen, and Bond); "supra" notes 3-4 (Zender Testimony and Ramanathan Testimony); "infra" notes 9 and 42 (Jacobson Testimony and Bond Testimony). ] .

Black carbon is formed through the incomplete combustion of fossil fuels, biofuel, and biomass, and is emitted in both anthropogenic and naturally occurring soot. Black carbon warms the planet by absorbing heat in the atmosphere and by reducing albedo, the ability to reflect sunlight, when deposited on snow and ice. Black carbon stays in the atmosphere from several days to weeks, whereas CO2 has an atmospheric lifetime of more than 100 years [V. Ramanathan & G. Carmichael, "supra" note 4, at 226.] .

Given black carbon’s relatively short lifespan, reducing black carbon emissions would reduce warming within weeks. Control of black carbon, “particularly from fossil-fuel sources, is very likely to be the fastest method of slowing global warming” in the immediate future, according to Dr. Mark Jacobson of Stanford University, and he believes that major cuts in black carbon emissions could slow the effects of climate change for a decade or two [Ramanathan Testimony, "supra" note 8, at 3 (“Thus a drastic reduction in BC has the potential of offsetting the CO2 induced warming for a decade or two.”).] . Reducing black carbon emissions could help keep the climate system from passing the tipping points for abrupt climate changes, including significant sea-level rise from the disintegration of the Greenland and/or Antarctic ice sheets [Timothy Lenton, Hermann Held, Elmar Kriegler, Jim Hall, Wolfgang Lucht, Stefan Rahmstorf, and Hans Joachim Schellnhuber, "Tipping elements in the Earth’s climate system", 105 PROC. OF THE NAT’L ACAD. OF SCI. 6 (12 February 2008) (“The greatest threats are tipping the Arctic sea-ice and the Greenland ice sheet. . .”); J. Hansen, "Climate Catastrophe", NEW SCIENTIST (28 July 2007) (...the primary issue is whether global warming will reach a level such that ice sheets begin to disintegrate in a rapid, non-linear fashion on West Antarctica, Greenland or both.”).] .

“ [E] missions of black carbon are the second strongest contribution to current global warming, after carbon dioxide emissions,” according to Dr. V. Ramanathan and Dr. G. Carmichael. [V. Ramanathan and G. Carmichael, "supra" note 1, at 221 (“. . . emissions of black carbon are the second strongest contribution to current global warming, after carbon dioxide emissions.”) Numerous scientists also calculate that black carbon may be second only to CO2 in its contribution to climate change, including Tami C. Bond & Haolin Sun, "Can Reducing Black Carbon Emissions Counteract Global Warming", ENVIRON. SCI. TECHN. (2005), at 5921 (“BC is the second or third largest individual warming agent, following carbon dioxide and methane.”); "and" J. Hansen, "A Brighter Future", 53 CLIMATE CHANGE 435 (2002), "available at" http://pubs.giss.nasa.gov/docs/2002/2002_Hansen_1.pdf (calculating the climate forcing of BC at 1.0 +/- 0.5 W/m2).] They calculate black carbon’s combined climate forcing at 1.0 – 1.2 W/m2, which “is as much as 55% of the CO2 forcing and is larger than the forcing due to the other [GHGs] such as CH₄, CFCs, N₂O or tropospheric ozone.” [V. Ramanathan and G. Carmichael, "supra" note 4, at 222.] Other scientists estimate the total magnitude of black carbon’s forcing between + 0.2 to 1.1 W/m with varying ranges due to uncertainties.2 (See Table 1.) This compares with the IPCC’s climate forcing estimates of 1.66 W/m2 for CO2 and 0.48 W/m2 for CH₄. (See Table 2.) [IPCC, "Technical Summary", in CLIMATE CHANGE 2007: THE PHYSICAL SCIENCE BASIS. CONTRIBUTION OF WORKING GROUP I TO THE FOURTH ASSESSMENT REPORT OF THE INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE, 21 (2007) "available at" http://www.ipcc.ch/ipccreports/ar4-wg1.htm.] In addition, black carbon forcing is two to three times as effective in raising temperatures in the Northern Hemisphere and the Arctic than equivalent forcing values of CO₂. [ James Hansen & Larissa Nazarenko, "Soot Climate Forcing Via Snow and Ice Albedos", 101 PROC. OF THE NAT’L ACAD. OF SCI. 423 (13 January 2004) (“The efficacy of this forcing is 2 (i.e. for a given forcing it is twice as effective as CO2 in altering global surface air temperature)”); "compare" Zender Testimony, "supra" note 7, at 4 (figure 3); See J. Hansen & L. Nazarenko, "supra" note 18, at 426. (“The efficacy for changes of Arctic sea ice albedo is >3. In additional runs not shown here, we found that the efficacy of albedo changes in Antarctica is also >3.”); "See also" Flanner, M.G., C.S. Zender, J.T. Randerson, and P.J. Rasch, "Present-day climate forcing and response from black carbon in snow", 112 J. GEOPHYS. RES. D11202 (2007) (“The forcing is maximum coincidentally with snowmelt onset, triggering strong snow-albedo feedback in local springtime. Consequently, the “efficacy” of black carbon/snow forcing is more than three times greater than forcing by CO2.”).]

Jacobson calculates that reducing fossil fuel and biofuel soot particles would eliminate about 40% of the net observed global warming [Gross global warming should result in about 2°C temperature rise. However, observed global warming is only about .8°C because cooling particles off set much of the warming. Reducing fossil fuel and biofuel soot would reduce about 40% of the observed warming and about 16% of the gross warming. Jacobson Testimony, "supra" note 13, at 3. (“The figure also shows that fossil-fuel plus biofuel soot may contribute to about 16% of gross global warming (warming due to all greenhouse gases plus soot plus the heat island effect), but its control in isolation could reduce 40% of net global warming.”).] . (See Figure 1.) In addition to black carbon, fossil fuel and biofuel soot contain aerosols and particulate matter that cool the planet by reflecting the sun’s radiation away from the Earth. [Jacobson Testimony, "id." at 4.] When the aerosols and particulate matter are accounted for, fossil fuel and biofuel soot are increasing temperatures by about 0.35°C [Jacobson Testimony, "id"] .

Black carbon alone is estimated to have a 20-year Global Warming Potential (GWP) of 4,470, and a 100-year GWP of 1,055-2,240 [Jacobson Testimony, "id." As an aerosol, there is not standardized formula for developing global warming potentials (GWP) for black carbon. However, attempts to derive GWP100 range from 190 – 2240 relative to CO₂. Jacobson M Z 2005 Correction to `control of fossil-fuel particulate black carbon and organic matter, possibly the most effective method of slowing global warming' 110 J. Geophysical Res. D14105 (2005) (GWP BC – 190); Hansen, J., Mki. Sato, P. Kharecha, G. Russell, D.W. Lea, and M. Siddall, 2007: Climate change and trace gases. Phil. Trans. Royal. Soc. A, 365, 1925 (GWP BC – 500); Bond, T. and Haolin, Sun, “Can Reducing Black Carbon Emissions Counteract Global Warming?” Envtl. Sci. &Tech., 5921 (August 2005) (GWP BC – 680); Jacobson Testimony, "supra" note 9 at 4 (GWP BC – 2240)] . Fossil fuel soot, as a result of mixing with cooling aerosols and particulate matter, has a lower 20-year GWP of 2,530, and a 100-year GWP of 840-1,280 [Jacobson Testimony, "supra" note 9, at 4.] .

Over the course of the century, however, the amount of these cooling aerosols in the atmosphere is expected to decrease, largely as a result of reductions in sulfur dioxide emissions. These reductions will unmask warming by other agents, such as black carbon, which these cooling aerosols currently help to offset. At the same time, under the IPCC A1B scenario, black carbon emissions are expected to double, further compounding their warming effect. [Levy, H. II, M.D., et. al., "Strong Sensitivity of late 21st century climate to projected change in short-lived air pollutants", 113 J. GEOPHYS. RES. D06102, 2 (2008) (BC and OC emissions, which are scaled to carbon monoxide (CO) emissions,increase continuously and almost double by 2100.); "id". (“These emissions are based on projections of technological change, economic and population growth, and regulatory action out to 2100.”)]

Black carbons effect on Himalayan glaciers

According to the IPCC, “the presence of black carbon over highly reflective surfaces, such as snow and ice, or clouds, may cause a significant positive radiative forcing.” [IPCC, "supra" note 13, at 397. (“While the radiative forcing is generally negative, positive forcing occurs in areas with a very high surface reflectance such as desert regions in North Africa, and the snow fields of the Himalayas.”); J. Hansen & L. Nazarenko, "supra" note 14, at 425. (The brown haze over India, heavy with fossil fuel and biofuel soot, reaches to the Himalayas. If prevailing winds deposit even a fraction of this soot on glaciers, the snow black carbon content could be comparable to that in the Alps.”).] The IPCC also notes that emissions from biomass burning, which usually have a negative forcing [J. Hansen, "et al.", Efficacy of Climate Forcing, 110 J. GEOPHYS. RES. D18104, 1 (2005), "available at" http://pubs.giss.nasa.gov/docs/2005/2005_Hansen_etal_2.pdf (Accounting for forcing efficacies and for indirect effects via snow albedo and cloud changes, we find that fossil fuel soot, defined as black carbon + OC (organic carbon), has a net positive forcing while biomass burning black carbon + OC has a negative forcing).] , have a positive forcing over snow fields in areas such as the Himalayas [IPCC, "supra" note 13, at 397.] .

Black carbon is a significant contributor to Arctic ice-melt, and reducing such emissions may be “the most efficient way to mitigate Arctic warming that we know of,” according to Dr. Charles Zender of the University of California, Irvine [Zender Testimony, "supra" note 3, at 6.] . The “climate forcing due to snow/ice albedo change is of the order of 1.0 W/m2 at middle- and high-latitude land areas in the Northern Hemisphere and over the Arctic Ocean.” [. Hansen & L. Nazarenko,"supra"note 14, at 425.] The “soot effect on snow albedo may be responsible for a quarter of observed global warming.” [. Hansen & L. Nazarenko, "id." at 428] “Soot deposition increases surface melt on ice masses, and the meltwater spurs multiple radiative and dynamical feedback processes that accelerate ice disintegration,” according to NASA scientists Dr. James Hansen and Dr. Larissa Nazarenko [Hansen & L. Nazarenko, "id." at 425] . As a result of this feedback process, “BC on snow warms the planet about three times more than an equal forcing of CO₂.” [See "supra" note 18] . When black carbon concentrations in the Arctic increase during the winter and spring due to Arctic Haze, surface temperatures increase by 0.5 C [P.K. Quinn, T.S. Bates, E. Baum, N. Doubleday, A.M. Fiore, M. Flanner, A. Fridlind, T.J. Garrett, D. Koch, S. Menon, D. Shindell, A. Stohl, and S.G. Warren. S"hort-lived Pollutants in the Arctic: Their Climate Impact and Possible Mitigation Strategies", 8 ATMOS. CHEM. PHYS. 1723, 1731 (2008); "See" David Shukman, "Vast Cracks Appear in Arctic Ice", BBC NEWS (23 May 2008), "available at" http://news.bbc.co.uk/2/hi/science/nature/7417123.stm (A recent expedition study by Canada confirmed vast cracks stretching for more than 10 miles on Ward Hunt)]

Black carbon emissions from northern Eurasia, North America, and Asia have the greatest absolute impact on Arctic warming. [P.K. Quinn, "supra" note 34, at 1732.] However, black carbon emissions actually occurring within the Arctic have a disproportionately larger impact per particle on Arctic warming than emissions originating elsewhere [ P.K. Quinn, "id"] . As Arctic ice melts and shipping activity increases, emissions originating within the Arctic are expected to rise [P.K. Quinn, "id." at 1732; J. Hansen & M. Sato, "et al.", "Dangerous Human-Made Interference with Climate: a GISS modelE Study 7" ATMOS. CHEM. PHYS. DISCUSS. 2287, 2298, 2296 (2007)(“We suggest that Arctic climate change has been driven as much by pollutants (03, its precursors CH4 and soot) as by CO₂ . . . .Thus, in that case, reduction of some of the pollutants [including soot] may make it possible to keep further Arctic warming very small and thus probably avoid loss of all sea ice.”).] .

In some regions, such as the Himalayas, the impact of black carbon on melting snowpack and glaciers may be equal to that of CO₂, [V. Ramanathan & G. Carmichael, "supra" note 1, at 221.] . Ramanathan & G. Carmichael, "supra" note 1, at 221. Warmer air resulting from the presence of black carbon in South and East Asia over the Himalayas contributes to a warming of approximately 0.6C [V. Ramanathan & G. Carmichael," supra" note 1, at 224] . An “analysis of temperature trends on the Tibetan side of the Himalayas reveals warming in excess of 1C..” [V. Ramanathan & G. Carmichael, "supra" note 1, at 224] . This large warming trend is the proposed causal factor for the accelerating retreat of Himalayan glaciers [V. Ramanathan & G. Carmichael, "supra" note 1, at 224] ,which threatens fresh water supplies and food security in China and India [Lester R. Brown, "Melting Mountain Glaciers Will Shrink Grain Harvests in China and India", PLAN B UPDATE, Earth Policy Institute (20 March 2008), "available at" http://www.earth-policy.org/Updates/2008/Update71.htm (Melting Himalayan glaciers will soon reduce water supply for major Chinese and Indian rivers (Ganges, Yellow River, Yangtze River) that irrigate rice and wheat crops that feed hundreds of millions and “could lead to politically unmanageable food shortages.”).] .

Major producers of black carbon

"By Region": Developed countries were once the primary source of black carbon emissions, but this began to change in the 1950’s with the adoption of pollution control technologies in those countries [V. Ramanathan & G. Carmichael, "supra" note 1, at 221 (“Until about the 1950s, North America and Western Europe were the major sources of soot emissions, but now developing nations in the tropics and East Asia are the major source problem.”).] . Whereas the U.S. emits about 21% of the world’s CO₂, it emits 6.1% of the world’s soot [Jacobson Testimony, "supra" note 9, at 4] . The Unites States and the European Union could further reduce their black carbon emissions by accelerating implementation of black carbon regulations that currently take effect in 2015 or 2020 [Clean Air Fine Particle Implementation Rule, 72 Fed. Reg. 20586, 20587 (April 25, 2007) (to be codified as 40 C.F.R. pt. 51), "available at" http://www.epa.gov/fedrgstr/EPA-AIR/2007/April/Day-25/a6347.pdf; Press Release, European Union, Environment: Commission welcomes final adoption of the air quality directive, (April 14, 2008), "available at" http://europa.eu/rapid/pressReleasesAction.do?reference=IP/08/570&format=HTML&aged=0&language=EN&guiLanguage=en.] and by supporting the adoption of pending International Maritime Organization (IMO) regulations [International Maritime Organization, Press Release, IMO Environment meeting Approves Revised Regulations on Ship Emissions, International Maritime Organization (4 April 2008)," available at" http://www.imo.org/About/mainframe.asp?topic_id=1709&doc_id=9123(The IMO has approved amendments to MARPOL Annex VI Regulations for the Prevention of Air Pollution from Ships which are now subject to adoption at an October 2008 meeting.).] . Existing regulations also could be expanded to increase the use of clean diesel and clean coal technologies and to develop second-generation technologies.

Today, the majority of black carbon emissions are from developing countries [Tami Bond, Testimony for the Hearing on Black Carbon and Climate Change, U.S. House Committee on Oversight and Government Reform 2-3 (October 18, 2007), "available at" http://oversight.house.gov/documents/20071018110647.pdf [hereinafter Bond Testimony] ] and this trend is expected to increase [Jacobson Testimony, "supra" note 9, at 5.] . The largest sources of black carbon are Asia, Latin America, and Africa. [Tami Bond, "Summary: Aerosols", Air Pollution as a Climate Forcing: A Workshop, Honolulu, Hawaii, April 29-May 3, 2002, "available at" http://www.giss.nasa.gov/meetings/pollution2002/] China and India account for 25-35% of global black carbon emissions [V. Ramanathan & G. Carmichael," supra" note 1, at 226] . Black carbon emissions from China doubled from 2000 to 2006. [V. Ramanathan & G. Carmichael, "supra" note 1, at 226 ] Existing and well-tested technologies used by developed countries, such as clean diesel and clean coal, could be transferred to developing countries to reduce their emissions [Ramanathan Testimony," supra" note 4, at 4] .

Black carbon emissions “peak close to major source regions and give rise to regional hotspots of black carbon—induced atmospheric solar heating.” [V. Ramanathan & G. Carmichael, "supra" note 1, at 221] . Such hotspots include, “the Indo-Gangetic plains in South Asia; eastern China; most of Southeast Asia including Indonesia; regions of Africa between sub-Sahara and South Africa; Mexico and Central America; and most of Brazil and Peru in South America.” [V. Ramanathan & G. Carmichael, id] . Approximately three billion people live in these hotspots. [V. Ramanathan & G. Carmichael, id]

"By Source": Approximately 20% of black carbon is emitted from burning biofuels, 40% from fossil fuels, and 40% from open biomass burning, according to Ramanathan. [V. Ramanathan & G. Carmichael, "id." at 224.] . Similarly, Dr. Tami Bond of the University of Illinois, Urbana Champaign, estimates the sources of black carbon emissions as follows: [See Bond Testimony, "supra" note 42, at 2 (figure 1)]

42% Open biomass burning (forest and savanna burning)

18% Residential biofuel burned with traditional technologies

14% Diesel engines for transportation

10% Diesel engines for industrial use

10% Industrial processes and power generation, usually from smaller boilers

6.0% Residential coal burned with traditional technologies [Bond Testimony," id." at 1-2.] Black carbon sources vary by region. For example, the majority of soot emissions in South Asia are due to biofuel cooking, whereas in East Asia, coal combustion for residential and industrial uses plays a larger role.

Fossil fuel and biofuel soot have significantly greater amounts of black carbon than climate-cooling aerosols and particulate matter, making reductions of these sources particularly powerful mitigation strategies. For example, emissions from the diesel engines and marine vessels contain higher levels of black carbon compared to other sources. [Jacobson Testimony, "supra" note 13, at 5-6 (showing that shipping emissions produce more than 3 times as much black carbon as POC, while off-road vehicles produce 40% more black carbon than POC, and on-road vehicles produce 25-60% more black carbon than POC).] Regulating black carbon emissions from diesel engines and marine vessels therefore presents a significant opportunity to reduce black carbon’s global warming impact. [Although shipping only accounts for 1.7% of the global black carbon inventory, given the expected increase in shipping throughout regions especially sensitive to black carbon like the Arctic, it still represents a strong option for black carbon reductions. Lack, D., B. Lerner, C. Granier, T. Baynard, E. Lovejoy, P. Massoli, A. R. Ravishankara, and E. Williams, Light absorbing carbon emissions from commercial shipping, 35 Geophysical Res. Letters L13815 (2008).]

Biomass burning emits greater amounts of climate-cooling aerosols and particulate matter than black carbon, resulting in short-term cooling. [J. Hansen "et al'., Efficacy of Climate Forcing, "supra" note 27] However, over the long-term, biomass burning may cause a net warming when CO₂ emissions and deforestation are considered. [Mark. Z. Jacobson, "The Short-Term Cooling but Long-Term Global Warming Due to Biomass Burning", 17 J. OF CLIMATE 2909, 2923 (“. . . whereas aerosol particles emitted during burning may cause a short-term cooling of global climate, longer-lived greenhouse gases may cause warming (or cancel the cooling) after several decades. As such, reducing biomass burning may cause short-term warming but long-term cooling or no change in temperature. Although the eventual cooling may not appear for many years, its magnitude may be as large as 0.6 K after 100 yr.”).] Reducing biomass emissions would therefore reduce global warming in the long-term and provide co-benefits of reduced air pollution, CO₂ emissions, and deforestation. Johannes Lehmann of Cornell University estimates that by switching to slash-and-char from slash-and-burn agriculture, which turns biomass into ash using open fires that release black carbon [Surabi Menon, James Hansen, Larissa Nazarenko, & Yunfeng Luo, "Climate Effects of Black Carbon", 297 SCIENCE 2250, 2250 (27 September 2002) (Black Carbon emissions are “a product of incomplete combustion from coal, diesel engines, biofuels, and outdoor biomass burning . . .”).] and GHGs, ["See" Lehmann, "et al., Bio-Char Sequestration in Terrestrial Ecosystems – A Review", 11 MITIGATION AND ADAPTATION STRATEGIES FOR GLOBAL CHANGE 403, at 403-07, 418 (Springer 2006), "available at" http://www.css.cornell.edu/faculty/lehmann/publ/MitAdaptStratGlobChange%2011,%20403-427,%20Lehmann,%202006.pdf ;" See id." at 407 (Researchers estimate that between 38-84% of the biomass carbon in vegetation is released during the burn, whereas converting the biomass into bio-char by means of simple kiln techniques sequesters more than 50% of this carbon in bio-char).] 12% of anthropogenic carbon emissions caused by land use change could be reduced annually, ["Id." at 407-08] which is approximately 0.66 Gt CO₂-eq. per year, or 2% of all annual global CO₂-eq emissions. ["See" Raupach, Michael, "et al., Global and Regional Drivers of Accelerating CO₂ Emissions", 104 PROC. OF THE NAT’L ACAD. OF SCI. 24, (underlying data "available at", http://www.pnas.org/cgi/content/full/0700609104/DC1) (indicating that between 2000-2005 land use emissions annually represented on average 1.5 GtC of the total 8.7 GtC global emissions or 5.5 Gt CO₂ eq. of 31.9 Gt CO₂ eq. of global emissions—17.25% of total. A reduction of 12% of land use emissions equals 0.66 Gt CO₂ eq., approximately 2% of annual global CO₂ eq. emissions. Lehmann’s original estimates were based on a 0.2 GtC offset of the 1.7 GtC emissions from land use change estimated in 2001 by the IPCC"). See also" Lehmann, "et al.", "supra" note 49, at 407-08. (Given the increase in fossil fuel emissions to 8.4 GtC, total anthropogenic emissions in 2006, including the estimated 1.5 GtC from land use change, were 9.9 GtC. Thus, despite an increase in overall CO₂ eq. emissions, using Lehmann’s original 0.2 GtC reduction still results in an approximate 2% reduction in global CO₂ eq. emissions). See Global Carbon Budget Team, Recent Carbon Trends and the Global Carbon Budget, the Global Carbon Project, (15 November 2007), "available at" http://www.globalcarbonproject.org/global/pdf/GCP_CarbonCycleUpdate.pdf (giving 2006 global carbon emissions estimates).]

Technology for reducing black carbon

Ramanathan notes that “developed nations have reduced their black carbon emissions from fossil fuel sources by a factor of 5 or more since 1950. Thus, the technology exists for a drastic reduction of fossil fuel related black carbon.” [Ramanathan Testimony, "supra" note 4, at 4.]

Jacobson believes that “ [g] iven proper conditions and incentives, [soot] polluting technologies can be quickly phased out. In some small-scale applications (such as domestic cooking in developing countries), health and convenience will drive such a transition when affordable, reliable alternatives are available. For other sources, such as vehicles or coal boilers, regulatory approaches may be required to nudge either the transition to existing technology or the development of new technology.” [Jacobson Testimony, "supra" note 9, at 5.]

Hansen states that “technology is within reach that could greatly reduce soot, restoring snow albedo to near pristine values, while having multiple other benefits for climate, human health, agricultural productivity, and environmental aesthetics. Already soot emissions from coal are decreasing in many regions with transition from small users to power plants with scrubbers.” [J. Hansen & L. Nazarenko, "supra" note 14, at 428]

Jacobson suggests converting “ [U.S.] vehicles from fossil fuel to electric, plug-in-hybrid, or hydrogen fuel cell vehicles, where the electricity or hydrogen is produced by a renewable energy source, such as wind, solar, geothermal, hydroelectric, wave, or tidal power. Such a conversion would eliminate 160 Gg/yr (24%) of U.S. (or 1.5% of world) fossil-fuel soot and about 26% of U.S. (or 5.5% of world) carbon dioxide.” [Jacobson Testimony, "supra" note 9, at 9.] According to Jacobson’s estimates, this proposal would reduce soot and CO₂ emissions by 1.63 GtCO₂–eq. per year. [Jacobson offers an estimate of total U.S. CO₂ emissions in 2005 of 6270 metric tonnes, 26% of which is 1630." Id."] He notes, however, “that the elimination of hydrocarbons and nitrogen oxides would also eliminate some cooling particles, reducing the net benefit by at most, half, but improving human health,” a substantial reduction for one policy in one country. [Jacobson Testimony, "supra" note 9, at 9]

For diesel vehicles in particular there are a several effective technologies available. Diesel oxidation catalysts have been in use for over 30 years, can be used on almost any diesel vehicle, and can eliminate 25-50% of black carbon emissions. [Manufacturers of Emission Controls Association (MECA), “Emission Control Technologies for Diesel-Powered Vehicles,” 9 (December 2007) (“Diesel oxidation catalysts installed on a vehicle’s exhaust system can reduce total PM typically by as much as 25 to over 50 percent by mass, under some conditions depending on the composition of the PM being emitted”), available at: http://www.meca.org/galleries/default-file/MECA%20Diesel%20White%20Paper%2012-07-07%20final.pdf.] Newer, more efficient diesel particulate filters (DPFs), or traps, can eliminate over 90% of black carbon emissions, ["Id.", (“DPFs can achieve up to, and in some cases, greater than a 90 percent reduction in PM. High efficiency filters are extremely effective in controlling the carbon fraction of the particulate, the portion of the particulate that some health experts believe may be the PM component of greatest concern”). ] but these devices require ultra low sulfur diesel fuel (ULSD). To ensure compliance with new particulate rules for new on-road and non-road vehicles in the U.S., the EPA first required a nationwide shift to ULSD, which allowed DPFs to be used in diesel vehicles in order to meet the standards. Because of recent EPA regulations, black carbon emissions from diesel vehicles are expected to decline about 70 percent from 2001 to 2020.” ["Id.", at 5, (“Mobile source black carbon emissions are estimated at 234 Gg in 2001, representing 54 percent of the nationwide black carbon emissions of 436 Gg. Under Scenario F, mobile source emissions are projected to decline to 71 Gg, a reduction of 163 Gg.”] Overall, “BC emissions in the United States are projected to decline by 42 percent from 2001 to 2020. [Bahner, Mark A., Weitz, Keith A., Zapata, Alexandra and DeAngelo, Benjamin, Use of Black Carbon and Organic Carbon Inventories for Projections and Mitigation Analysis,” 1, (2007) available at: http://www.epa.gov/ttn/chief/conference/ei16/session3/k.weitz.pdf.] By the time the full fleet is subject to these rules, EPA estimates that over 239,000 tons of particulate matter will be reduced annually. [EPA, Heavy-Duty Highway Diesel Program, available at: http://www.epa.gov/oms/highway-diesel/index.htm (“Once this action is fully implemented…Soot or particulate matter will be reduced by 110,000 tons a year”); EPA, Clean Air Nonroad Diesel Rule—Facts and Figures, available at: http://www.epa.gov/nonroad-diesel/2004fr/420f04037.htm (“Environmental Benefits When the Fleet of Older Nonroad Engines Has Fully Turned Over by 2030: Annual reductions of Fine PM (PM2.5): 129,000 tons”).] Outside of the US diesel oxidation catalysts are often available and DPFs will become available as ULSD is more widely commercialized.

Another technology for reducing black carbon emissions from diesel engines is to shift fuels to compressed natural gas. In New Delhi, India, a court-ordered shift to compressed natural gas for all public transport vehicles, including buses, taxis, and rickshaws, resulted in a climate benefit, “largely because of the dramatic reduction of black carbon emissions from the diesel bus engines.” [Conor C. O. Reynolds & Milind Kandlikar, "Climate Impacts of Air Quality Policy: Switching to a Natural Gas-Fueled Public Transportation System in New Delhi", ENVIRON. SCI. TECHNOL. (forthcoming 2008) (“When aerosol emissions are included, the switch to CNG fueling results in a climate benefit, largely because of the dramatic reduction of black carbon emissions from the diesel bus engines”). The fuel switching policy was implemented with the aid of the Indian Supreme Court. "See" Urvashi Narain and Ruth Greenspan Bell, "Who Changed Delhi’s Air? The Roles of the Court and the Executive in Environmental Policymaking", Resources for the Future Discussion Paper 05-48 (December 2005) http://www.rff.org/rff/documents/rff-dp-05-48.pdf (" [T] he main role of the Supreme Court was to force the government to implement previously announced policies. … [T] he Delhi experience for instituting change has become a model for other Indian cities as well as neighboring countries.")] Overall, the fuel switch for the vehicles reduced black carbon emissions enough to produce a 10 percent net reduction in CO2-eq., and perhaps as much as 30 percent. [Conor C. O. Reynolds & Milind Kandlikar, "Climate Impacts of Air Quality Policy: Switching to a Natural Gas-Fueled Public Transportation System in New Delhi", ENVIRON. SCI. TECHNOL. (forthcoming 2008) (“However, when aerosol emissions are taken into account in our model, the net effect of the switch is estimated to be a 10% reduction in CO2(e), and there may be as much as a 30% reduction in CO2(e)”).] The main gains were from diesel bus engines whose CO2-eq. emissions were reduced 20 percent. ["Id.", at Section 3.1 (“In total there is about a 10% reduction of net CO2(e) emissions, and if buses are considered separately, net CO2(e) emissions are reduced by about 20%”). ] According to a study examining these emissions reductions, “there is a significant potential for emissions reductions through the [UNFCCC] Clean Development for such fuel switching projects.” [C. O. Reynolds & Milind Kandlikar, "Climate Impacts of Air Quality Policy: Switching to a Natural Gas-Fueled Public Transportation System in New Delhi", 1, ENVIRON. SCI. TECHNOL. (forthcoming 2008).]

Technologies are also in development to reduce some of the 133,000 metric tons of particulate matter emitted each year from ships. [Lack, D., B. Lerner, C. Granier, T. Baynard, E. Lovejoy, P. Massoli, A. R. Ravishankara, and E. Williams, "Light absorbing carbon emissions from commercial shipping", 35 Geophysical Res. Letters L13815 (2008).] Ocean vessels use diesel engines, and particulate filters similar to those in use for land vehicles are now being tested on them. As with current particulate filters these too would require the ships to use ULSD, but if comparable emissions reductions are attainable, up to 120,000 metric tons of particulate emissions could be eliminated each year from international shipping. That is, if particulate filters could be shown reduce black carbon emissions 90 percent from ships as they do for land vehicles, 120,000 metric tons of today’s 133,000 metric tons of emissions would be prevented. [That is, if particulate filters could be shown reduce black carbon emissions 90 percent from ships as they do for land vehicles, 120,000 metric tons of today’s 133,000 metric tons of emissions would be prevented.] Other efforts can reduce the amount of black carbon emissions from ships simply by decreasing the amount of fuel the ships use. By traveling at slower speeds or by using shore side electricity when at port instead of running the ship’s diesel engines for electric power, ships can save fuel and reduce emissions.

Reynolds and Kandlikar estimate that the shift to compressed natural gas for public transport in New Delhi ordered by the Supreme Court reduced climate emissions by 10 to 30%. [Conor C. O. Reynolds & Milind Kandlikar, "Climate Impacts of Air Quality Policy: Switching to a Natural Gas-Fueled Public Transportation System in New Delhi", ENVIRON. SCI. TECHNOL. (forthcoming 2008) (“Between 2001 and 2003, public transport vehicles in New Delhi were required to switch their fuel to natural gas in an attempt to reduce their air pollution impacts. … [W] hen [black carbon and other] aerosol emissions are taken into account in our model, the net effect of the switch is estimated to be a 10% reduction in CO₂ (eq), and there may be as much as a 30% reduction…. There is a significant potential for emissions reductions through the [UNFCCC] Clean Development for such fuel switching projects.”) The fuel switching policy was implemented with the aid of the Indian Supreme Court. See Urvashi Narain and Ruth Greenspan Bell, "Who Changed Delhi’s Air? The Roles of the Court and the Executive in Environmental Policymaking," Resources for the Future Discussion Paper 05-48 (December 2005) http://www.rff.org/rff/documents/rff-dp-05-48.pdf (" [T] he main role of the Supreme Court was to force the government to implement previously announced policies. … [T] he Delhi experience for instituting change has become a model for other Indian cities as well as neighboring countries.")]

Ramanathan estimates that “providing alternative energy-efficient and smoke-free cookers and introducing transferring technology for reducing soot emissions from coal combustion in small industries could have major impacts on the radiative forcing due to soot.” [V. Ramanathan & G. Carmichael, "supra" note 4, at 226.] Specifically, the impact of replacing biofuel cooking with black carbon-free cookers (solar, bio, and natural gas) in South and East Asia is dramatic: over South Asia, a 70 to 80% reduction in black carbon heating; and in East Asia, a 20 to 40% reduction.” [V. Ramanathan & G. Carmichael, "id."]

In Delhi, India, a court-ordered shift to compressed natural gas for public transport is estimated to have reduced climate emissions by 10 to 30%. [Conor C. O. Reynolds & Milind Kandlikar, "Climate Impacts of Air Quality Policy: Switching to a Natural Gas-Fueled Public Transportation System in New Delhi", ENVIRON. SCI. TECHNOL. (forthcoming 2008) (“Between 2001 and 2003, public transport vehicles in New Delhi were required to switch their fuel to natural gas in an attempt to reduce their air pollution impacts. … [W] hen [black carbon and other] aerosol emissions are taken into account in our model, the net effect of the switch is estimated to be a 10% reduction in CO2 (eq), and there may be as much as a 30% reduction…. There is a significant potential for emissions reductions through the [UNFCCC] Clean Development for such fuel switching projects.”) The fuel switching policy was implemented with the aid of the Indian Supreme Court. "See" Urvashi Narain and Ruth Greenspan Bell, "Who Changed Delhi’s Air? The Roles of the Court and the Executive in Environmental Policymaking", Resources for the Future Discussion Paper 05-48 (December 2005) http://www.rff.org/rff/documents/rff-dp-05-48.pdf (" [T] he main role of the Supreme Court was to force the government to implement previously announced policies. … [T] he Delhi experience for instituting change has become a model for other Indian cities as well as neighboring countries.")]

Public health and food security

Public health benefits of particulate matter reductions have been recognized for years. The WHO estimates that air pollution causes nearly two million premature deaths per year. [http://www.who.int/mediacentre/factsheets/fs313/en/index.html] By reducing black carbon, a primary component of fine particulate matter, the health risks from air pollution will decline. In fact, public health concerns have given rise to leading to many efforts to reduce such emissions, for example, from diesel vehicles and cooking stoves. Since black carbon has a damaging impact on plants, reducing it also benefits agriculture.

Regulation of black carbon

Many countries have existing national laws to regulating black carbon emissions, including laws that address particulate emissions. Some examples include:

*banning or regulating slash-and-burn clearing of forests and savannahs;
*requiring shore-based power/electrification of ships at port, regulating idling at terminals, and mandating fuel standards for ships seeking to dock at port;
*requiring regular vehicle emissions tests, retirement, or retrofitting (e.g. adding particulate traps [O. Boucher and M.S. Reddy, "Climate trade-off between black carbon and carbon dioxide emissions", 36 ENERGY POLICY 193, 196-198 (2007) (Particulate traps on diesel engines reduce black carbon emissions and associated climate forcing but are partially offset by an increase in fuel consumption and CO₂ emissions. Where the fuel penalty is 2-3%, black carbon reductions will produce positive benefits for the climate for the first 28-68 years, assuming reduction in black carbon emission is 0.15­0.30 g/mile, CO₂ emissions are 1500­2000 g/mile, and a 100-year GWP of 680 is used for black carbon. The net positive benefits for climate will continue for up to centuries in northern regions because of black carbon's effect on snow and ice albedo).] ), including penalties for failing to meet air quality emissions standards, and heightened penalties for on-the-road “super-emitting” vehicles;
*banning or regulating the sale of certain fuels and/or requiring the use of cleaner fuels for certain uses;
*limiting the use of chimneys and other forms of biomass burning in urban and non-urban areas;
*requiring permits to operate industrial, power generating, and oil refining facilities and periodic permit renewal and/or modification of equipment; and
*requiring filtering technology and high-temperature combustion (e.g. super-critical coal) for existing power generation plants, and regulating annual emissions from power generation plants.

The International Network for Environmental Compliance & Enforcement recently issued a Climate Compliance Alert on Black Carbon. [http://inece.org/climate/INECEClimateComplianceAlert_BlackCarbon.pdf]

"Table 1 : Estimates of Black Carbon Climate (Radiative) Forcings by Effect"

"Table 2: Estimated Climate Forcings (W/m2)"

References

*Institute for Governance & Sustainable Development, http://www.igsd.org; International Network for Environmental Compliance & Enforcement, http://www.inece.org.

Endnotes

See also

* Carbon black
* Global dimming
* Slash and burn

Contributors

* Gregory Carmichael - [http://www.cbe.engineering.uiowa.edu/faculty/carmichael/]
* V. Ramanathan - [http://sio.ucsd.edu/Profile/?who=vramanathan]
* Tami Bond - [http://cee.uiuc.edu/research/bondresearch/abstract.htm]
* Charles Zender - [http://www.ess.uci.edu/~zender/]
* Mark Jacobson - [http://www.stanford.edu/group/efmh/jacobson/]
* James Hansen - [http://www.columbia.edu/~jeh1/]

[cite web
url=http://www.nature.com/ngeo/journal/v1/n4/abs/ngeo156.html
title=Nature Geoscience: Global and regional climate changes due to black carbon
accessdate$1=$2$3-$4-$5

*Institute for Governance & Sustainable Development, http://www.igsd.org; International Network for Environmental Compliance & Enforcement, http://www.inece.org.