technologies in those countries. Whereas the United States emits about 21% of the world's CO2, it emits 6.1% of the world's soot. The European Union and United States might further reduce their black carbon emissions by accelerating implementation of black carbon regulations that currently take effect in 2015 or 2020 and by supporting the adoption of pending International Maritime Organization (IMO) regulations. 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 and this trend is expected to increase. The largest sources of black carbon are Asia, Latin America, and Africa. China and India together account for 25–35% of global black carbon emissions. Black carbon emissions from China doubled from 2000 to 2006. 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. Black carbon emissions are highest in and around major source regions. This results in regional hotspots of atmospheric solar heating due to black carbon. Hotspot areas include: the Indo-Gangetic plains of India eastern China most of Southeast Asia and Indonesia equatorial regions of Africa Mexico and Central America most of Brazil and Peru in South America. Approximately three billion people live in these hotspots. By source Approximately 20% of black carbon is emitted from burning biofuels, 40% from fossil fuels, and 40% from open biomass burning. Similar estimates of the sources of black carbon emissions are as follows: 42% Open biomass burning. (forest and savanna burning) 18% Residential biomass 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% Residential coal burned with traditional technologies. Black carbon sources vary by region. For example, the majority of soot emissions in South Asia are due to biomass cooking, whereas in East Asia, coal combustion for residential and industrial uses plays a larger role. In Western Europe, traffic seems to be the most important source since high concentrations coincide with proximity to major roads or participation to (motorized) traffic. Fossil fuel and biomass 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