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(UNEP/WMO 2011). This 2011 joint report entitled ‘Integrated Assessment of Black Carbon and Tropospheric Ozone’ found that reducing SCLPs ‘now will slow the rate of climate change within the first half of the century’ and that a small number of focused emission reduction strategies targeting BC and O₃ could immediately ‘slow the rate of climate change within the first half of the century’ (UNEP/WMO 2011, p. 1). BC is a major component of soot and exists as particles in the atmosphere. Emissions that result from the incomplete/inefficient combustion of solid fuels and traditional biomass are released as a mixture of health‐damaging indoor air pollutants such as BC that have short atmospheric life spans and result in significant negative impacts on human health and climate change particularly at the national and regional levels. Ozone, at the ground level, is an air pollutant that is harmful to health and ecosystems and is a major component of urban smog. Throughout the troposphere, or lower atmosphere, ozone is also a significant GHG. Ozone is not directly emitted but is produced from emissions of precursors, of which CH₄ and carbon monoxide are of particular relevance in this study. By contrast, ozone in the stratosphere is considered to be beneficial in protecting life from the sun’s harmful ultraviolet (UV) radiation (UNEP/WMO 2011, p. 7).

In 2012, the governments of Bangladesh, Canada, Ghana, Mexico, Sweden and the United States, along with UNEP, came together to initiate efforts to treat SLCPs as an urgent and collective challenge. Together, they formed the Climate & Clean Air Coalition (CCAC), which now comprises a voluntary partnership of governments and non‐governmental organizations (NGOs), and aimed at including cities and other NNSAs, to support linked action on several challenges: climate, public health, energy access and food security. Box 1.2 excerpted from the CCAC website provides a succinct overview of the importance of curbing SLCPs.

Box 1.2 What are short‐lived climate pollutants? (Excerpted from Climate & Clean Air Coalition)

       What are short‐lived climate pollutants?

      Short‐lived climate pollutants are powerful climate forcers that remain in the atmosphere for a much shorter period of time than carbon dioxide (CO₂), yet their potential to warm the atmosphere can be many times greater. Certain short‐lived climate pollutants are also dangerous air pollutants that have harmful effects for people, ecosystems and agricultural productivity.

      The short‐lived climate pollutants black carbon, methane, tropospheric ozone, and hydrofluorocarbons are the most important contributors to the man‐made global greenhouse effect after carbon dioxide, responsible for up to 45% of current global warming. If no action to reduce emissions of these pollutants is taken in the coming decades, they are expected to account for as much as half of warming caused by human activity.

      Source: CCAC website 2021.

So, the first question is what is the UN‐led global community doing about curbing the four principal SLCPs: BC, methane (CH₄), tropospheric ozone (O₃) and HFCs? A joint paper published by World Resources Institute (WRI) and Oxfam highlighted several key issues including that: ‘early and ambitious action’ to reduce SLCPs are ‘essential to achieving the goals of’ the PA and the Sustainable Development Goals (SDGs); actions to curb ‘highly potent’ SLCPs are critical in ensuring that the threshold of 1.5°C is not crossed ‘which will affect poor and vulnerable communities first and worst’; and actions aimed at reducing SLCPs also ‘delivers multiple benefits for development and human well‐being, supporting efforts to improve health, enhance food security, and alleviate poverty’. Equally significantly, the paper also pointed out that: ‘actions to mitigate these potent pollutants were often underrepresented in the first nationally determined contributions (NDCs) submitted by Parties to the Paris Agreement’ (Ross et al. 2018, p. 1). But, the main challenge to date is that there is no global or regionally relevant pollution mitigation strategy or protocol that covers emissions of SLCPs, particularly BC that covers the needs of those countries and communities where the problem of BC‐related PM pollution is most severely experienced. More recently, there has been an increasing push towards addressing the mitigation of HFCs within the context of the Kigali Amendment to the Montreal Protocol, and CH₄ is a recognized GHG that is technically covered within the context of the voluntary national reporting requirements of the PA. To be clear, the focus of this book is primarily on the linkages between PM pollution, health and climate inequities and more circumscribed to understanding the relevance of curbing BC.

      From the immediate perspective of this book, the decades‐old intergovernmental negotiations on climate change have consistently not addressed the issue of SLCPs like BC and O₃, both of which have major public health impacts that negatively constrain the lives of poorest communities within developing countries and cities, particularly those in Asia and Africa.

      BC is a solid particle or aerosol, not a gas, and results from emissions from gas and diesel engines, coal‐fired power plants and other sources including solid biomass (solid fuels). Atmospheric BC concentrations have been related to anthropogenic activities, and BC emission reductions represent a potential mitigation strategy that could reduce global climate forcing from anthropogenic activities in the short term and slow the associated rate of climate change (UNEP/WMO 2011; Bond et al. 2013). Curbing SLCPs and thereby mitigating toxic levels of air pollution can offer short‐term climate mitigation benefits, but what is often ignored and urgently needs to be highlighted is that increasing access to clean energy for all and transitioning to low carbon energy future provides valuable cost savings from human health perspectives in individual countries.

      Reducing PM 2.5 emissions are critically important from a human health perspective, but what is often not reflected is that one of the principal components of PM 2.5 – BC emitted as a result of incomplete combustion of solid fuels has also been identified as an SLCP. While emission reductions of CO₂ are absolutely integral to addressing anthropogenic climate change, SLCPs like BC, a component of PM pollution, have been found to contribute directly to adverse impacts on human health, leading to premature deaths worldwide, and also negatively impact on agriculture and rainfall patterns. An extensive, landmark cross‐national research assessment of the role of BC emissions specified that the predominant sources of BC are combustion related, namely, fossil fuels for transportation, solid fuels for industrial and residential uses and open burning of biomass. The assessment estimated BC to be: ‘… the second most important human emission in terms of its climate forcing in the present‐day atmosphere; only carbon dioxide is estimated to have a greater forcing. Sources that emit black carbon also emit other short‐lived species that may either cool or warm climate’ (Bond et al. 2013, p. 5381).

Arguably, the nexus between increasing access to clean air, curbing fossil fuel related PM pollution and addressing climate change matters now more than ever for millions of lives that are amongst the poorest and most vulnerable in cities and communities. Highlighting the findings of new collaborative research on clean air and climate change conducted by Duke University, NASA and other entities on 48 contiguous US states and major cities before the US Congress, Drew Shindell (who heads CCAC Scientific Advisory Panel and is a lead author for the IPCC) provided a forceful case to prioritize climate change related health benefits of clean air in the US:

      ‘Over the next 50 years, keeping to the 2°C pathway would prevent roughly 4.5 million premature deaths, about 3.5 million hospitalizations and emergency room visits, and approximately 300 million lost workdays in the US. These large impacts reflect our updated understanding of the severe toxicity of air pollution and the dangers of heat exposure. Although it does not appear on death certificates it is indirectly responsible for a substantial fraction of heart diseases, including strokes, and respiratory diseases, including lower respiratory infections and chronic obstructive pulmonary disease.

      The economic value of these health and labor benefits is enormous. The avoided deaths are valued at more than $37 trillion. The avoided health care spending due to reduced hospitalizations and emergency room visits exceeds $37 billion, and the increased labor productivity is valued at more than

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