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The "black carbon" is said to be the second most important man-made agent of climate change.
Huge quantities of man-made soot enter the atmosphere every year. It has a greenhouse effect two-thirds that of carbon dioxide, and greater than methane.
A major constituent of soot, black carbon is the most solar energy-absorbing component of particulate matter and can absorb one million times more energy than CO2. The amount of energy stored in the atmosphere is measured as watts per square meter of Earth’s surface; a 2013 study estimated black carbon’s effect to be 1.1 watts per square meter per year, second only to carbon dioxide, which is responsible for 1.56 watts per square meter. In other words, black carbon is the second largest contributor to climate change after CO2. But unlike CO2, which can stay in the atmosphere for hundreds to thousands of years, black carbon, because it is a particle, remains in the atmosphere only for days to weeks before it returns to earth with rain or snow.
Because black carbon absorbs solar energy, it warms the atmosphere. When it falls to earth with precipitation, it darkens the surface of snow and ice, warming the snow, and hastening melting.
BC plays a far greater role in global warming than previously believed and is second only to CO2 in the amount of heat it traps in the atmosphere. Reducing some forms of soot emissions such as from diesel fuel and coal burning could prove effective in slowing down the planet’s warming.
BC is the most strongly absorbing component of fine particulate matter (PM2.5) and contributes to regional and global climate change in the near-term (over months to a few decades). Reducing BC emissions can help slow the rate of climate change, reduce local air pollution, improve human health and security of food and water supplies, and support achieving the Sustainable Development Goals (SDGs).
BC affects the climate system through several different mechanisms, including the following, which are ranked by level of understanding and relative effects:
· directly absorbing incoming solar radiation, primarily in visible wavelengths;
· darkening snow and ice, thereby reducing the albedo and so reducing reflection of solar radiation, which tends to accelerate melting; and
· changing the number and composition of the small particles on which water vapor condenses, affecting the lifetime, reflectivity and stability of clouds (U.S. EPA, 2012; Bond et al., 2013; IPCC, 2014).
black carbon plays a much bigger role in global warming than many scientists previously thought. According to the new analysis, it is second only to carbon dioxide in the amount of heat it traps in the atmosphere
