Part 2 of 2: 2010 March 16: U.S. House of Representatives Hearing: Ramanathan testimony on Black Carbon

BC and Eurasian Snow CoverSpringtime warming and reduced snow cover from carbonaceous particlesM. G. Flanner1, C. S. Zender2, P. G. Hess1,3, N. M. Mahowald1,3, T. H. Painter4, V. Ramanathan5, and P. J. Rasch1Equilibrium climate experiments suggest that fossil fuel and biofuel emissions of BC+OM induce 95% as much springtime snow cover loss over Eurasia as anthropogenic carbon dioxide, a consequence of strong snow-albedo feedback and large BC+OM emissions from Asia. ACPD 8, 19819-19859, 2008
Testimony of V. Ramanathan March 16, 2010 9
the major source for some of the observed drying of the land regions of the planet (e.g. India&northern China) during the last 50 years (Ramanathan et al, 2005 and Meehl et al, 2008). Regionally aerosol induced radiative changes (forcing) are an order of magnitude larger than that of the greenhouse gases, but because of the global nature of the greenhouse forcing, its global climate effects are still more important. However there is one important distinction to be made. While the warming due to the greenhouse gases is projected to increase global average rainfall, the large reduction in surface solar radiation due to absorbing aerosols would offset it.
11. Challenges and Opportunities for Mitigation: BC‘s warming effect presents an opportunity to reduce projected warming in the short term (as also suggested by others, e.g. Hansen and Sato, 2001; Jacobson, 2002; Bond and Sun, 2005). My thesis is that, BC reductions have the potential to forestall the onset of the so-called dangerous climate change. For example, a reduction of BC emissions by about 50%, may reduce the radiative forcing by about 0.2 Wm-2 to 0.5 Wm-2. In comparison, if CO2 continues to increase at the current rate of increase, it will add about 0.2 to 0.3 Wm-2 per decade. Thus a drastic reduction in BC has the potential to offset CO2induced warming for a decade or two. Effectively, BC reduction may provide a possible mechanism for buying time to develop and implement effective steps for reducing CO2 emissions. The following issues need to be factored in further consideration of this proposal:
i) The life time of BC is of the order of days to several weeks, depending on the location. Thus the BC concentration and its global heating will decrease almost immediately after reduction of its emission;
ii) Inhalation of soot is a major public health issue. For example, in India, alone it is estimated inhalation of indoor smoke is responsible for over 400,000 deaths annually (mostly among women and children;
Smith, 2000). Air pollution related fatalities for Asia is estimated (Pachauri and Sridharan, 1998) to be over one million (indoor smoke inhalation and outdoor brown clouds). Thus reduction of BC emissions may be warranted from public health considerations alone.
iii) The developed nations have reduced their BC
emissions from fossil fuel sources significantly since the 1960s. Thus the technology exists for a drastic reduction of fossil fuel related BC. With respect to biofuel cooking, it can be reduced if not eliminated, by providing alternate cooking methods in rural areas in Asia and Africa. But we need to conduct a careful and well documented scientific study of the impact of BC reduction on radiative forcing and its cost effectiveness. Towards this goal, this author along with a team of NGOs, public health experts and alternate energy experts, has proposed Project Surya (http://www-ramanathan.ucsd.edu/ProjectSurya.html), that will adopt a large rural area of about 50,000 population, in India, and provide alternate cooking with biogas plants, smoke free cookers and solar cookers. The objectiveof this experiment is to estimate from observationsthe warming potential of BC. Surya will also assessthe impact of BC reduction on human health and the cost of reducing BC emissions from biofuels. Results from this pilot experiment will be used to scale up similar efforts throughout the subcontinent.
iv) Long range transport of BC is an important factor for policy discussion of BC mitigation. For example, studies have show
n that transport of BC from E. Asia across the pacific is a major source of BC above one km in altitude over California (Hadley et al, 2007). Likewise, BC from N. America and Europe deposits on snow and sea ice in the Arctic. BC from S. Asia and E. Asia surrounds the Himalayan-Tibetan mountain ranges.
v) The notion that we may reach a level of dangerous climate change during this century is increasingly perceived as a possibility. Given this development, options for mitigating such dangerous climate changes are being explored worldwide. The present BC reduction proposal should also be considered in this context, and by no means
is BC reduction being proposed by this author as an alternative to CO2 reduction. At best, it is a short term measure, to buy a decade or two time for implementing CO2 emission reduction.
Major Uncertainties: Our ability to model the effects of BC in climate models is severely limited. One of the main reasons is the large uncertainty (factor of 2 or more) in the current estimates of the emission of organic (OC) and elemental carbon (EC) (See Bond et al, 2004; 2007). Furthermore, biomass burning contributes significantly to the emissions of OC and EC and the historical trends (during the last 100 years) in these emissions are unknown. Models currently resort to adhoc methods such as scaling the present day emissions with past trends in population.
Testimony of V. Ramanathan March 16, 2010 10BC has two competing effects inside clouds. Mixtures of BC with sulfates or organics can become cloud nuclei and in turn enhance the number of cloud drops. This in turn can lead to a decrease in drop size, an increase in cloud lifetime followed by an increase in reflection of solar radiation. In addition, the a decrease in drop size can suppress rain formation. On the other hand, the large solar heating of the cloudy skies by BC can decrease relative humidity and evaporate clouds, which can lead to increased penetra-tion of sunlight to the ground and warming of the surface. These two competing effects have been examined with surface data (Kaufman and Koren, 2006) over several continental and marine locations. These data suggest that the warming effect of BC dominates the cooling effect of BC-Organic-Sulfate mixtures. Satellite data over Amazon have been used to examine the net inter-action of BC laden biomass burning smoke with clouds. This study (Koren et al, 2004) also showed that the smoke lead to dissipation of low clouds. Similarly, cloud coverage in highly polluted E Asia exhibited a long term declining trend (Qian et al, 2006). Acknowledgements The research reported here was funded and supported by NSF (J. Fein); NOAA (C. Koblinsky); NASA (H. Maring); California Energy Commission(G Franco). References: Andreae, M.O., Gelencser, A. Black carbon or brown carbon? The nature of light-absorbing carbonaceous aerosols, Atmos. Chem. Phys. 6, 3131-3148 (2006). 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, Global Biogeochem. Cycles 21, GB2018, doi:10.1029/2006GB002840 (2007). Bond, T.C. & Sun, H. Can reducing black carbon emissions counteract global warming? Environ. Sci. Technol. 39, 5921-6 (2005). Bond, T. C. et al. A technology-based global inven-tory of black and organic carbon emissions from combustion. J. Geophys. Res. 109, D14203, doi:10.1029/2003JD003697 (2004). Chung, C. E., and Ramanathan,V. Weakening of North Indian SST Gradients and the Monsoon Rainfall in India and the Sahel, J.Climate 19, 2036-2045 (2006). Chung, S. H., and J. H. Seinfeld, Global dis-tribution and climate forcing of carbona-ceous aerosols, J. Geophys. Res. 107, 4407, doi:10.1029/2001JD001397 (2002). Flanner, M.G., C.S. Zender, P.G. Hess, N.M. Mahowald, T.H. Painter, V. Ramanathan, and P.J. Rasch. Springtime warming and reduced snow cover from carbonaceous particles. Atmos. Chem. Phys. 9, 2481-2497, (2009). Forster, P. & Ramanswamy, V. et al. in Climate Change 2007: The Physical Science Basis – Con-tribution of Working Group I to the Fourth Assess-ment Report of the Intergovernmental Panel on Climate Change (eds Solomon, S. et al.) (Cam-bridge Univ. Press, Cambridge, UK, New York, USA, 2007). Hadley, O.L., V. Ramanathan, G.R. Carmichael, Y. Tang, G.C. Roberts, and G.S. Mauger. Trans-Pacific transport of black carbon and fine aerosols (D < 2.5μm) into North America. J. Geophys. Res. 112, D05309, doi:10.1029/2006JD007632 (2007). Hansen, J. E.; Sato,M. Trends of measured climate forcing agents. Proc. Natl. Acad. Sci. 98(26), 14778-14783 (2001). Jacobson, M. Z. Short-term effects of controlling Fossil-fuel soot, Biofuel soot and Gases, and Me-than on Climate, Arctic Ice, and Air pollution, J. Geophys. Res. (submitted, 2010) Jacobson, M. Z. Climate response of fossil fuel and biofuel soot, accounting for soot’s feedback to snow and sea ice albedo and emissivity. J. Geophys. Res. 109, D21201, doi:10.1029/2004JD004945 (2004). Jacobson, M. Z. Control of fossil-fuel particulate black carbon and organic matter, possibly the most effec-tive method of slowing global warming. J. Geo-phys. Res. 107, 4410, doi: 10.1029/2001JD001376 (2002). Jacobson, M. Z. Strong radiative heating due to the mixing state of black carbon in atmospheric aero-sols. Nature 409, 695-697 (2001). Kaufman, Y.J., and Koren,I. Smoke and Pollution aerosol effect on cloud cover, Science 313, 655-658 (2006). Koren, I., Kaufman, Y.J., Remer, L.A., Martins, J.V. Measurement of t he Effect of Amazon Smoke on inhibition of cloud formation, Science 303, 1342- 1345 (2004). T estimony of V. Ramanathan March 16, 2010 11
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Testimony of V. Ramanathan March 16, 2010
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