Black carbon
Black carbon warms the Earth by absorbing sunlight and heating the atmosphere and by reducing albedo when deposited on snow and ice (direct effects) and indirectly by interaction with clouds, with the total forcing of 1.1 W/m2.
[5] The IPCC and other climate researchers have posited that reducing black carbon is one of the easiest ways to slow down short term global warming.
[17] The disastrous effects of coal pollution on human health and mortality in the early 1950s in London led to the UK Clean Air Act 1956.
In the less-developed regions of the world where there were limited or no controls on soot emissions the air quality continued to degrade as the population increased.
A purely scattering aerosol will reflect energy that would normally be absorbed by the earth-atmosphere system back to space and leads to a cooling effect.
Alternative methods rely on satellite based measurements of optical depth for large areas or more recently on spectral noise analysis for very local concentrations.
One of the major uncertainties in modeling the effects of the Arctic haze on the solar radiation balance was limited knowledge of the vertical distributions of black carbon.
[26] These measurements showed substantial concentrations of black carbon found throughout the western Arctic troposphere including the North Pole.
[27] Optical depths of these magnitudes lead to a substantial change in the solar radiation balance over the highly reflecting Arctic snow surface during the March–April time frame of these measurements modeled the Arctic aerosol for an absorption optical depth of 0.021 (which is close to the average of an internal and external mixtures for the AGASP flights), under cloud-free conditions.
[44] 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.
[46] Biomass burning emits greater amounts of climate-cooling aerosols and particulate matter than black carbon, resulting in short-term cooling.
[51] In a research study published in June 2022,[52] atmospheric scientist Christopher Maloney and his colleagues noted that rocket launches release tiny particles called aerosols in the stratosphere and increase ozone layer loss.
[54] Black carbon is a form of ultrafine particulate matter, which when released in the air causes premature human mortality and disability.
In addition, atmospheric black carbon changes the radiative energy balance of the climate system in a way that raises air and surface temperatures, causing a variety of detrimental environmental impacts on humans, on agriculture, and on plant and animal ecosystems.
Concentrations of black carbon decrease sharply with increasing distance from (traffic) sources which makes it an atypical component of particulate matter.
[67] By reducing black carbon, a primary component of fine particulate matter, the health risks from air pollution will decline.
In fact, public health concerns have given rise to leading to many efforts to reduce such emissions, for example, from diesel vehicles and cooking stoves.
Semi-direct effect Black carbon absorb incoming solar radiation, perturb the temperature structure of the atmosphere, and influence cloud cover.
Based on the IPCC estimate, it would be reasonable to conclude that the combined direct and indirect snow albedo effects for black carbon rank it as the third largest contributor to globally averaged positive radiative forcing since the pre-industrial period.
[91] The "climate forcing due to snow/ice albedo change is of the order of 1.0 W/m2 at middle- and high-latitude land areas in the Northern Hemisphere and over the Arctic Ocean.
[93][94] Black carbon emissions also significantly contribute to Arctic ice-melt, which is critical because "nothing in climate is more aptly described as a 'tipping point' than the 0 °C boundary that separates frozen from liquid water—the bright, reflective snow and ice from the dark, heat-absorbing ocean.
"[95] Black carbon emissions from northern Eurasia, North America, and Asia have the greatest absolute impact on Arctic warming.
[5] Warmer air resulting from the presence of black carbon in South and East Asia over the Himalayas contributes to a warming of approximately 0.6 °C.
[100] This large warming trend is the proposed causal factor for the accelerating retreat of Himalayan glaciers,[5] which threatens fresh water supplies and food security in China and India.
[83][109] Jacobson calculates that reducing fossil fuel and biofuel soot particles would eliminate about 40% of the net observed global warming.
In addition to black carbon, fossil fuel and biofuel soot contain aerosols and particulate matter that cool the planet by reflecting the sun's radiation away from the Earth.
[117] The Integrated Assessment of Black Carbon and Tropospheric Ozone published in 2011 by the United Nations Environment Programme and World Meteorological Organization calculates that cutting black carbon, along with tropospheric ozone and its precursor, methane, can reduce the rate of global warming by half and the rate of warming in the Arctic by two-thirds, in combination with CO2 cuts.
"[3] Hansen states that "technology is within reach that could greatly reduce soot, restoring snow albedo to near pristine values, while having multiple other benefits for climate, human health, agricultural productivity, and environmental aesthetics.
In New Delhi, India, the supreme court ordered shift to compressed natural gas for all public transport vehicles, including buses, taxis, and rickshaws, resulted in a climate benefit, "largely because of the dramatic reduction of black carbon emissions from the diesel bus engines".
Reynolds and Kandlikar estimate that the shift to compressed natural gas for public transport in New Delhi ordered by the Supreme Court reduced climate emissions by 10 to 30%.
