Publications

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2019
Lelieveld, J, Klingmuller K, Pozzer A, Burnett RT, Haines A, Ramanathan V.  2019.  Effects of fossil fuel and total anthropogenic emission removal on public health and climate. Proceedings of the National Academy of Sciences of the United States of America. 116:7192-7197.   10.1073/pnas.1819989116   AbstractWebsite

Anthropogenic greenhouse gases and aerosols are associated with climate change and human health risks. We used a global model to estimate the climate and public health outcomes attributable to fossil fuel use, indicating the potential benefits of a phaseout. We show that it can avoid an excess mortality rate of 3.61 (2.96-4.21) million per year from outdoor air pollution worldwide. This could be up to 5.55 (4.52-6.52) million per year by additionally controlling nonfossil anthropogenic sources. Globally, fossil-fuel-related emissions account for about 65% of the excess mortality, and 70% of the climate cooling by anthropogenic aerosols. The chemical influence of air pollution on aeolian dust contributes to the aerosol cooling. Because aerosols affect the hydrologic cycle, removing the anthropogenic emissions in the model increases rainfall by 10-70% over densely populated regions in India and 10-30% over northern China, and by 10-40% over Central America, West Africa, and the droughtprone Sahel, thus contributing to water and food security. Since aerosols mask the anthropogenic rise in global temperature, removing fossil-fuel-generated particles liberates 0.51(+/- 0.03) degrees C and all pollution particles 0.73(+/- 0.03) degrees C warming, reaching around 2 degrees C over North America and Northeast Asia. The steep temperature increase from removing aerosols can be moderated to about 0.36(+/- 0.06) degrees C globally by the simultaneous reduction of tropospheric ozone and methane. We conclude that a rapid phaseout of fossil-fuel-related emissions and major reductions of other anthropogenic sources are needed to save millions of lives, restore aerosol-perturbed rainfall patterns, and limit global warming to 2 degrees C.

2009
Ramanathan, V, Feng Y.  2009.  Air pollution, greenhouse gases and climate change: Global and regional perspectives. Atmospheric Environment. 43:37-50.   10.1016/j.atmosenv.2008.09.063   AbstractWebsite

Greenhouse gases (GHGs) warm the Surface and the atmosphere with significant implications for rainfall, retreat of glaciers and sea ice, sea level, among other factors. About 30 years ago, it was recognized that the increase in tropospheric ozone from air pollution (NO(x), CO and others) is an important greenhouse forcing term. In addition, the recognition of chlorofluorocarbons (CFCs) on stratospheric ozone and its climate effects linked chemistry and climate strongly. What is less recognized, however, is a comparably major global problem dealing with air pollution. Until about ten years ago, air pollution was thought to be just an urban or a local problem. But new data have revealed that air pollution is transported across continents and ocean basins due to fast long-range transport, resulting in trans-oceanic and trans-continental plumes of atmospheric brown Clouds (ABCs) containing sub micron size particles, i.e., aerosols. ABCs intercept Sunlight by absorbing as well as reflecting it, both of which lead to a large surface dimming. The dimming effect is enhanced further because aerosols may nucleate more cloud droplets, which makes the clouds reflect More solar radiation. The dimming has a Surface cooling effect and decreases evaporation of moisture from the surface, thus slows down the hydrological cycle. On the other hand, absorption of solar radiation by black carbon and some organics increase atmospheric hearing and tend to amplify greenhouse warming of the atmosphere. ABCs are concentrated in regional and mega-city hot spots. Long-range transport from these hot spots causes widespread plumes over the adjacent oceans. Such a pattern Of regionally concentrated Surface dimming and atmospheric Solar heating, accompanied by widespread dimming over the oceans, gives rise to large regional effects. Only during the last decade, we have begun to comprehend the surprisingly large regional impacts. In S. Asia and N. Africa, the large north-south gradient in the ABC dimming has altered both the north-south gradients in sea Surface temperatures and land-ocean contrast in surface temperatures, which in turn slow down the monsoon circulation and decrease rainfall over the continents. On the other hand, heating by black carbon warms the atmosphere at elevated levels from 2 to 6 kin, where most tropical glaciers are located, thus strengthening the effect of GHGs on retreat of snow packs and glaciers in the Hindu Kush-Himalaya-Tibetan glaciers. Globally, the surface cooling effect of ABCs may have masked as Much 47% of the global warming by greenhouse gases, with an uncertainty range of 20-80%. This presents a dilemma since efforts to curb air pollution may unmask the ABC cooling effect and enhance the surface warming. Thus efforts to reduce GHGs and air pollution should be done under one common framework. The uncertainties in our understanding of the ABC effects are large, but we are discovering new ways in which human activities are changing the climate and the environment. (C) 2008 Elsevier Ltd. All rights reserved.