Contrails and contrail-cirrus may be the largest source of radiative forcing (RF) attributable to aviation. Biomass-derived alternative jet fuels are a potentially major way to mitigate the climate impacts of aviation by reducing lifecycle CO2 emissions. Given the up to 90% reduction in soot emissions from paraffinic biofuels, the potential for a significant impact on contrail RF due to the reduction in contrail-forming ice nuclei (IN) remains an open question. We simulate contrail formation and evolution to quantify RF over the United States under different emissions scenarios. Replacing conventional jet fuels with paraffinic biofuels generates two competing effects. First, the higher water emissions index results in an increase in contrail occurrence (similar to +8%). On the other hand, these contrails are composed of larger diameter crystals (similar to +58%) at lower number concentrations (similar to -75%), reducing both contrail optical depth (similar to -29%) and albedo (similar to -32%). The net changes in contrail RF induced by switching to biofuels range from -4% to +18% among a range of assumed ice crystal habits (shapes). In comparison, cleaner burning engines (with no increase in water emissions index) result in changes to net contrail RF ranging between -13% and +5% depending on habit. Thus, we find that even 67% to 75% reductions in aircraft soot emissions are insufficient to substantially reduce warming from contrails, and that the use of biofuels may either increase or decrease contrail warming-contrary to previous expectations of a significant decrease in warming.

Black carbon (BC) aerosols are one of the most uncertain drivers of global climate change. The prevailing view is that BC mass concentrations are low in rural areas where industrialization and vehicular emissions are at a minimum. As part of a national research program called the Ganga Basin Ground Based Experiment-2014 under the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) Phase-III of Ministry of Earth Sciences, Government of India, the continuous measurements of BC and particulate matter (PM) mass concentrations, were conducted in a rural environment in the highly-polluted Indo-Gangetic Plain region during 16th June to 15th August (monsoon period), 2014. The mean mass concentration of BC was 4.03 (+/- 0.85) mu g m(-3) with a daily variability between 2.4 and 5.64 mu g m(-3), however, the mean mass PM concentrations [near ultrafine (PM1.0), fine (PM2.5) and inhalable (PM1.0)] were 29.1(+/- 16.2), 34.7 (+/- 19.9) and 43.7 (+/- 283) mu g m(-3), respectively. The contribution of BC in PM1.0 was approximately 13%, which is one of the highest being recorded. Diurnally, the BC mass concentrations were highest (mean: 5.89 mu g m(-3)) between 20:00 to 22:00 local time (LT) due to the burning of biofuels/biomass such as wood, dung, straw and crop residue mixed with dung by the local residents for cooking purposes. The atmospheric direct radiative forcing values due to the composite and BC aerosols were determined to be +78.3, +44.9, and +45.0 W m(-2) and +42.2, +35.4 and +34.3 W m(-2) during the months ofJune, July and August, respectively. The corresponding atmospheric heating rates (AHR) for composite and BC aerosols were 2.21,1.26 and 1.26; and 1.19, 0.99 and 0.96 K day(-1) for the month ofJune, July and August, respectively, with a mean of 1.57 and 1.05 K day(-1) which was 33% lower AHR (BC) than for the composite particles during the study period. This high AHR underscores the importance of absorbing aerosols such as BC contributed by residential cooking using biofuels in India. Our study demonstrates the need for immediate, effective regulations and policies that mitigate the emission of BC particles from domestic cooking in rural areas of India. (C) 2016 Elsevier B.V. All rights reserved.

Climate change will alter ecosystem metabolism and may lead to a redistribution of vegetation and changes in fire regimes in Northern Eurasia over the 21st century. Land management decisions will interact with these climate-driven changes to reshape the region's landscape. Here we present an assessment of the potential consequences of climate change on land use and associated land carbon sink activity for Northern Eurasia in the context of climate-induced vegetation shifts. Under a `business-as-usual' scenario, climate-induced vegetation shifts allow expansion of areas devoted to food crop production (15%) and pastures (39%) over the 21st century. Under a climate stabilization scenario, climate-induced vegetation shifts permit expansion of areas devoted to cellulosic biofuel production (25%) and pastures (21%), but reduce the expansion of areas devoted to food crop production by 10%. In both climate scenarios, vegetation shifts further reduce the areas devoted to timber production by 6-8% over this same time period. Fire associated with climate-induced vegetation shifts causes the region to become more of a carbon source than if no vegetation shifts occur. Consideration of the interactions between climate-induced vegetation shifts and human activities through a modeling framework has provided clues to how humans may be able to adapt to a changing world and identified the trade-offs, including unintended consequences, associated with proposed climate/energy policies.

Black carbon (BC) is an important aerosol species because of its global and regional influence on radiative forcing and its local effects on the environment and human health. We have estimated the emissions of BC in China, where roughly one-fourth of global anthropogenic emissions is believed to originate. China's high rates of usage of coal and biofuels are primarily responsible for high BC emissions. This paper pays particular attention to the application of appropriate emission factors for China and the attenuation of these emissions where control devices are used. Nevertheless, because of the high degree of uncertainty associated with BC emission factors, we provide ranges of uncertainty for our emission estimates, which are approximately a factor of eight. In our central case, we calculate that BC emissions in China in 1995 were 1342 Gg, about 83% being generated by the residential combustion of coal and biofuels, We estimate that BC emissions could fall to 1224 Gg by 2020. This 9% decrease in BC emissions can be contrasted with the expected increase of 50% in energy use; the reduction will be obtained because of a transition to more advanced technology, including greater use of coal briquettes in place of raw coal in cities and towns. The increased use of diesel vehicles in the future will result in a greater share of the transport sector in total BC emissions. Spatially, BC emissions are predominantly distributed in an east-west swath across China's heartland, where the rural use of coal and biofuels for cooking and heating is widespread. This is in contrast Lo the emissions of most other anthropogenically derived air pollutants. which are closely tied to population and industrial centers. (C) 2001 Elsevier Science Ltd. All rights reserved.