Life-Cycle and Effects of Black Carbon
Black carbon is usually produced due to the incomplete combustion of fossil fuels and vegetation. Black carbon comes under the category of particulate matter however, and cannot exactly be called a greenhouse gas, although it can stay airborne for up to a few days or weeks. Black carbon occurs ubiquitously on the Earth’s surface and occurs on soil, sediments, frozen surfaces and also the atmosphere. Its main heat absorbing constituents are the aerosols present in it consisting of fine solid or liquid particles.
Black carbon’s brief atmospheric lifespan means that its effects on the Earth’s climate are regional, such as due to the melting of ice in the Arctic and in Himalayan glaciers. However, Seiler and Crutzen’s (1980) study of black carbon formed in vegetation fires suggested that black carbon might act as a carbon sink due to this form of carbon not degrading over time and could in fact store carbon over long periods of geological time.
Black carbon can also represent a significant portion of the carbon pool of Earth’s oceans in the form of carbonaceous aerosol deposits. The extraordinary problems caused by black carbon therefore, is its presence on frozen surfaces on Earth, causing them to melt and contribute to sea level rise.
Black carbon’s slow atmospheric lifespan could mean that its effects would stop exacerbating if anthropogenic carbon emissions were reduced. This means that reducing anthropogenic carbon emissions would greatly help reduce the short-term effects of global warming, especially the effects of climate change on sea level rise due to the melting of frozen regions.
Although black carbon has immense effects on climate change, many people however, see black carbon as more of a health threat than a threat to the Earth’s climate. According to the Centre for Science & Environment (CSE), the form of black carbon that is detrimental to human health is particulate black carbon of the size PM 2.5. These fine particles can be airborne and affect the respiratory and cardiovascular systems in the human body. According to an estimate by the World Health Organization (WHO) in 2009, about 3.1 million people worldwide, most of whom are from developing countries, suffer premature deaths due to inhalation of these PM 2.5 particles.
The effects of black carbon on the Earth’s climate, however, can go beyond merely melting frozen surfaces. Black carbon as a warming agent is different from organic carbon, which is a cooling agent. With significant effects on weather and climate, black carbon particles are able to influence cloud formation and their lifetimes, rainfall and other related weather patterns.
Black carbon particles can also influence temperature contrasts between regions, thereby influencing not just precipitation, but also wind patterns. The effects however, are accompanied with large deposits of black carbon and trace amounts although, are sufficient to melt frozen matter on the Earth’s surface.
Black Carbon and India
The largest amount of emissions of black carbon occur in the developing countries, especially from large emitters such as India and China which emit about 25 to 35 per cent of total global black carbon emissions (CSE, 2012). Due to the close proximity of the Himalayas to sources of black carbon emissions, high quantities of black carbon are said to be deposited in the Himalayas.
Black carbon had become a focal point in the Kyoto Protocol (2001), with the US citing its exclusion in the document as the reason for America’s withdrawal from the agreement. Although the US has expressed its readiness to include black carbon in international protocols, India has remained reluctant to enter into agreements that include black carbon.
Contrary to some studies that propose that global warming will not be reduced by black carbon mitigation measures, many entities believe that black carbon mitigation is a possible and doable solution to climate change.
The US formed a coalition including many Western countries and the UN in 2012 for short-term solutions for climate change involving carbon black mitigation. The focus is jointly on black carbon along with hydrofluorocarbons and methane, with black carbon and methane being significant sources of Arctic melting. The imperatives for their solutions are on national action plans and policy imperatives including capacitation in developing countries.
In India the Indian Space Research Organization (ISRO) is carrying out research on the impacts of aerosols in the Indo-Gangetic Plains. The project is called the ISRO-Geosphere Biosphere Programme and is meant to measure black carbon.
A large amount of agricultural waste burning and firewood burning along with fossil fuel combustion takes place in the region. These effects are significantly intense during the winter months due to the stillness of air, low precipitation and the burning of agricultural waste.
Black Carbon in the Himalayas
In a study by R. Zhang et al. (2015) titled ‘Quantifying sources, transport, deposition, and radiative forcing of black carbon over the Himalayas and Tibetan Plateau’ on the effects of black carbon in the Himalayas and the Tibetan Plateau, the transport, deposition and radiative forcing of black carbon was quantified for the region.
The first correlation transmitted by the study confirmed that airborne and deposited black carbon is affecting the melting of snow and glacier retreat. The study undertook to quantify the source-receptor relationships of black carbon due to the impacts of anthropogenic activity and black carbon emissions on the Himalayas and in the Tibetan Plateau.
Their analysis of the source-receptor relationships in black carbon dispersion reveals that the dispersal sourced from separate geographical areas is dependent on the season and the locational peculiarities of the Himalayas and the Tibetan Plateau.
The largest contribution annually, however, comes from biomass and biofuel emissions from South Asia, with the second-largest contribution coming from fossil fuel emissions from South Asia, followed in turn by fossil fuel emissions from East Asia. These contributions are constant for all seasons except for the summer season, when fossil fuel emissions from East Asia become a larger contributor.
The study found that the largest burden on black carbon dispersal in the Himalayas was placed upon by biomass, biofuel and fossil fuel emissions from South Asia. The effects of black carbon emissions on the Tibetan Plateau were more location-specific, with emissions from East Asia contributing to dispersal in the northeastern plateau while emissions from Central Asia and the Middle East having an effect on black carbon dispersal in the northwestern plateau.
This process was accentuated during the summer season, with higher dispersal especially from East Asia during the summer months. These dispersals effect both the melting of snow and glacier retreat in the Himalayas and in the Tibetan Plateau.
Black Carbon in the Arctic
In a study by C. Jiao and M.G. Flanner (2016) titled ‘Changing black carbon transport to the Arctic from present day to the end of 21st Century’, they report on how Arctic wind patterns have changed due to an alteration in the winter polar dome structure that is due to loss of sea ice and surface warming, particularly in the Chukchi Sea region.
The wind pattern that results from this change favours the transport of East Asian aerosol emissions and inhibits North American aerosol emissions from travelling polewards. Computer simulations based on present day emissions also point towards a reduction of the Arctic annual mean burden by between 13.6 per cent and 61 per cent due to black carbon by the end of the 21st Century.
In the Arctic, even organic carbon, which tends to scatter sunlight and thus is a cooling agent, combines with black carbon to form soot, which is a carbonaceous substance that exhibits high heat absorption. The black carbon emissions from the inhabited land hemispheres which are most likely to reach the Arctic region are most likely to come northwards from 40oN, with the maximum contributions expected to come from regions falling in these latitudes (K. Bice et al., 2009). The effects of black carbon and other aerosols cumulatively on the Arctic are believed to be disproportionate by the scientific community.
Conclusion
One of the greatest challenges to checking black carbon emissions is that a large and growing fraction of black carbon emissions come from developing countries that still have many inefficient methods of combusting material that could produce black carbon. On the other hand, most mitigation measures develop in the more developed nations, many of which are located close to the Arctic Circle while most developing countries are located closer to the equatorial regions.
The highest emissions have come from India, China and Southeast Asia. Here the constraints on reducing black carbon emissions based on finance and industrial framework and capacity are also the greatest. Mitigation here could include technology for and R&D on low emissions, a proper energy infrastructure based on proper regulations, and proper urban, industrial and rural administration. In what is largely a by-process of production processes, a best practices approach is a necessity.
