Energy Access and Climate Mitigation and Adaptation

Facts and Figures

• The number of people relying on unsustainable cooking energy has increased from 2.6 billion (2013) to 3 billion (2015).
• Cookstoves generate the most black carbon emissions in the developing regions. Black Carbon (BC) is a major constituent of particulate matter (PM) from biomass combustion.
• Black Carbon is the 2nd largest contributor to global warming after CO2. The warming effect is expected to be about 2/3 of CO2.
• 60-80% of black carbon emissions in the developing regions are from biomass cookstoves.
• Almost 8.5 billion tons of atmospheric carbon dioxide – or about 18 percent of all anthropogenic carbon dioxide emissions – comes from biomass burning, according to Prof. Mark Jacobson from Stanford university

Biomass Burning

Burning of biomass generates carbon compounds such as carbon dioxide, methane, tiny bits of soot called black carbon and motes of associated substances called brown carbon.

Black Carbon is generated by the incomplete combustion of fossil fuels, biofuels and biomass. It is a strongly light-absorbing particulate matter that absorbs solar radiation at all wavelength.​ 

Brown carbon (BrC) is also a carbon based particulate matter that absorbs solar radiation within the visible and ultraviolet wavelength. 

Exposure to these pollutants during biomass burning is one of the major cause of premature deaths. Every year, more than 4 million people die from illness caused by indoor air pollution. The pollutants also causes cardiovascular disease, respiratory illness, lung cancer, asthma and low birth weights.

For more information about indoor air pollution , see the article on Indoor Air Pollution (IAP) andIndoor Air Pollution (IAP) Measurement

Effect of Black Carbon on Climate

Black and brown carbon particles causes atmospheric warming in three ways:

Direct effects

Black carbon absorbs both the incoming and outgoing solar radiation at all wavelength and thus lead to the atmosphere warming. The green house gases (GHG) only trap the outgoing infrared radiation from the earth's surface.

Warming of clouds

Black and brown carbon, in the atmospheric surface enter the minuscule water droplets that form clouds. During day time, the sunlight penetrates the water droplet and is absorbed by the carbon particles, creating heat and accelerating the evaporation of the water droplets. Similarly, the carbon particles floating in between the water droplets spaces also absorb the sunlight resulting in additional heating. Heating the cloud reduces its relative humidity and causes the clouds to dissipate. Cloud acts as a buffer between the earth and the sun, reflecting the sunlight back to the atmosphere. with increased dissipation of the cloud, less sunlight will be reflected and more will be absorbed, resulting in the warming of the earth.

Snow/albedo Effect

White surface result more light as compared to darker surfaces. Therefore, snow and ice effectively reflect sunlight and are vital in balancing the atmospheric temperature. Black carbon deposited on snow and ice darkens the surface and decrease the reflectivity of the surface (albedo effect). Black carbon can also absorb solar radiation in all wavelength and thus, the BC deposited on the snow accelerates the melting of the snow,exposing the dark soil and the dark seas underneath. Since these surfaces are dark, they contribute to further warming.

Net Effect of Black Carbon

To understand the net effect of black carbon on atmospheric warming, it is important to take into account the following points:

• Black carbon is not emitted alone but rather with other particles such as sulfur dioxide (SO2) , nitrogen oxides (NOx) and organic carbon. Some of these particles have a cooling effect on the climate. Therefore to calculate the net effect of black carbon, the cooling effect of co-emitted pollutants has to be offset.
• The atmospheric processes such as  mixing, aging, and coating occur after the BC is emitted and can influence its effect on climate

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Carbon Debt

The extraction, transportation and combustion of biomass releases a significant amount of carbon into the atmosphere. This carbon is added to the atmosphere and it takes time before it is balanced by the ecosystem. According to a report by IPCC on renewable energy sources and climate change mitigation (2011), it can take decades, even centuries, before ecosystems; in particular forests can recapture the carbon that has been released during biomass combustion . This creates a "carbon debt" in the atmosphere. Therefore, burning of solid biomas might not be "carbon neutral".

Potential Measures

To combat this situation, following potential measures/solutions could be applied:

• Promotion of clean cookstoves - it is estimated that some modern biomass stove models can reduce CO₂ emissions by 25-50%.

• Transitioning to agricultural waste briquettes - such as those made from sawdust, and crop residues and pellets (from compressed woodwaste, invasive plants, etc.) that can be burned in highly efficient residential gasifier stoves.

• More efficient production of charcoal or reducing overall production of charcoal.

• Switching to alternative fuels such as LPG, biogas, and bioethanol.

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Further Information

• Climate Change Mitigation and Adoption Potential of Basic Energy Services (GIZ, 2015)
  
• Household Cookstoves, Environment, Health and Climate Change – A New Look at an Old Problem (WB 2010)
  
• On thin Ice: How Cutting Pollution Can Slow Warming and Save Lives (WB 2013)
  
• Black Carbon Finance Study Group Report 2015
  
• Effects of biomass burning on climate, accounting for heat and moisture fluxes, black and brown carbon , and could absorption effects (Jacobsen, Journal of Geophysical research: Atmospheres. 2014)
  

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