The Integrated Assessment of Black Carbon and Tropospheric Ozone addresses the short-lived cli- mate forcers (SLCFs) that also have an impact on air quality. Its findings on both the state of scientific knowledge and existing policy options to cut emissions come from 50 authors convened by UNEP and WMO. Previous assessments have often studied either the impacts on climate from such pollutants or the direct effects of air pollution on human health and ecosystems, but not both in an integrated manner. This report gives a comprehensive assessment of the multiple benefits of practi- cal measures to reduce emissions of black carbon – a key component of soot – and the gases leading to the formation of tropospheric ozone, especially methane.
Issue of Our Planet, the magazine of the United Nations Environment Programme.
Current emissions of anthropogenic greenhouse gases (GHGs) have already committed the planet to an increase in average surface temperature by the end of the century that may be above the critical threshold for tipping elements of the climate system into abrupt change with potentially irreversible and unmanageable consequences. This would mean that the climate system is close to entering if not already within the zone of ‘‘dangerous anthropogenic interference’’ (DAI). Scientific and policy literature refers to the need for ‘‘early,’’ ‘‘urgent,’’ ‘‘rapid,’’ and ‘‘fast-action’’ mitigation to help avoid DAI and abrupt climate changes. We define ‘‘fast-action’’ to include regulatory measures that can begin within 2–3 years, be substantially implemented in 5–10 years, and produce a climate response within decades. We discuss strategies for short-lived non-CO2 GHGs and particles, where existing agree- ments can be used to accomplish mitigation objectives. Policy makers can amend the Montreal Protocol to phase down the production and consumption of hydrofluorocarbons (HFCs) with high global warming potential. Other fast-action strategies can reduce emissions of black carbon particles and precursor gases that lead to ozone formation in the lower atmosphere, and increase biosequestration, including through biochar. These and other fast- action strategies may reduce the risk of abrupt climate change in the next few decades by complementing cuts in CO2 emissions.
