Wednesday, 20 January 2021

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Four-Year Study Finds Black Carbon Second Biggest Climate Pollutant, Behind Carbon Dioxide

15jan-unepBlack carbon is the second most powerful climate pollutant, ahead of methane, and second only to carbon dioxide, according to a landmark four-year assessment lead by T.C. Bond, S. J. Doherty, D. W. Fahey, and P. Forster, and a multinational team of 27 other experts, including prominent scientists from China and India. Their results, Bounding the role of black carbon in the climate system, are scheduled to be published online Tuesday in the Journal of Geophysical Research: Atmospheres.

According to the assessment, the direct effects of black carbon are nearly twice as large as the 2007 IPCC Fourth Assessment, and in the past its climate impacts have been seriously underestimated, confirming select earlier studies that were once considered outliers, including a study by Ramanathan and Carmichael (2008).

“This landmark assessment shows that the potential to slow warming by cutting black carbon is even more important than previously understood,” said Durwood Zaelke, President of the Institute for Governance & Sustainable Development, who served as a reviewer of the assessment.

“The best estimate of industrial-era climate forcing of black carbon through all forcing mechanisms, including clouds and cryosphere forcing, is +1.1 Wm-2,” according to the assessment.  The upper end of possible total climate forcing from black carbon could be as high as 2.1Wm-2, more than the current forcing from CO2, at 1.7 Wm-2.

The assessment also calculates that BC causes significantly higher forcing over the Arctic and other vulnerable regions. It can also affect rainfall patterns in areas where emissions are high, such as the Asian Monsoon system, confirming earlier studies by Ramanathan et al. (2005) and Meehl et al. (2007).  In addition, the assessment establishes that black carbon is a significant cause of the rapid warming in the Northern Hemisphere at mid- to high-latitudes, including the northern United States, Canada, northern Europe, and northern Asia.

The assessment establishes that reducing diesel black carbon emissions along with other key sectors including brick kilns and residential solid fuel burning will quickly reduce warming.

"This new research provides further compelling evidence to act on short-lived climate pollutants, including black carbon," said Achim Steiner, UN Under-Secretary-General and UN Environment Programme Executive Director.  "I would urge more countries, companies and organizations to join the Climate and Clean Air Coalition, which is leveraging several key pathways and new partnerships to manage down these climate, health and crop-damaging emissions."  The Coalition has projects underway to reduce black carbon emissions from heavy-duty diesel vehicles and engines, brick production, and municipal waste disposal, and is considering several new initiatives, including for residential cook stoves.

Since its founding February last year, the Coalition has grown from six to 25 State partners from both developed and developing countries, including Nigeria, Ghana, Bangladesh, Mexico, Norway, Japan, and the U.S.  In May the G8 countries agreed to join, and commissioned the World Bank to prepare a report on ways to integrate reduction of near-term climate pollutants into their activities. Pending completion of the report, the World Bank has already pledged significant increases in funding to reduce black carbon and the other short-lived climate pollutants.  Other members include the UN Environment Programme, which houses the Secretariat, the UN Development Programme, and the European Commission, as well as several NGOs.  The Coalition’s total membership is 49.

“The Coalition is the first global effort to address black carbon and the other short-lived climate pollutants and is an essential platform for action,” said Romina Picolotti, former secretary of environment for Argentina. “States interested in doing more to reduce their black carbon emissions should not miss the opportunity to join.”

“Black carbon is not only more important for climate than we thought, it also kills over a million people every year from breathing air polluted by black carbon and contracting deadly respiratory diseases,” said Zaelke. “That number is expected to rise to 3.6 million deaths by 2050.  Black carbon is bad for development, which depends on a healthy population, and we need to reduce it now.”

Over the past decade “the speed of Arctic climate change and glacial melt has increased the demand for mitigation options which can slow near-term warming,” according to the assessment, and reducing black carbon along with other short-lived climate pollutants, “especially methane and tropospheric ozone (O3), could quickly decrease positive climate forcing and hence climate warming.” 

Black Carbon is one of three short-lived climate pollutants targeted for reduction by the Climate and Clean Air Coalition, along with methane and HFCs.  Fast action on black carbon and methane has the potential to cut the rate of climate change in half for the next several decades, reduce air pollution-related deaths by as much as 2.4 million a year, and annual crop losses by 30 to more than 100 million tonnes, according to a previous assessment of black carbon and tropospheric ozone by UNEP and the World Meteorological Organization.

The new assessment is being released at the same time as the US’s draft third climate assessment report by 240 scientists, which concludes that climate change is already a major threat, “largely because society and its infrastructure were designed for the climate of the past, not for the rapidly changing climate of the present or the future,” with longer periods of extreme heat in summer, longer wildfire seasons in the Western US, increasing coastal erosion, and more frequent flooding.

"Fast cuts to black carbon and other short-lived climate pollutants are critical for both mitigation and adaptation,” said Zaelke, “because they can quickly reduce the rate of warming by half and reduce impacts significantly over the next several decades.” “Success also builds the momentum and confidence we need to address carbon dioxide from energy production, which is essential for a safe climate,” he added.

The new assessment and the Coalition are clear that cuts in black carbon and the other short-lived climate pollutants cannot alone protect the Planet and its people from dangerous levels of climate change over the 21st century unless aggressive reductions are also made in carbon dioxide, the primary greenhouse gas.

The assessment will be available on the UNEP website, Tuesday 15 January at 14:00 CET: here.

Source: UNEP News

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