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Chapter 25 in Health of People, Health of Planet and Our Responsibility: Climate Change, Air Pollution and Health (Al-Delaimy, W. K., Ramanathan, & V., Sorondo, M. S. eds). Springer, Cham. Pages 321-331.

Climate change is becoming an existential threat with warming in excess of 2 °C within the next three decades and 4–6 °C within the next several decades. Warming of such magnitudes will expose as many as 75% of the world’s population to deadly heat stress in addition to disrupting the climate and weather worldwide. Climate change is an urgent problem requiring urgent solutions. This chapter lays out urgent and practical solutions that are ready for implementation now, will deliver benefits in the next few critical decades, and place the world on a path to achieving the long-term targets of the Paris Agreement. The approach consists of four building blocks and three levers to implement ten scalable solutions described in this chapter. These solutions will enable society to decarbonize the global energy system by 2050 through efficiency and renewables, drastically reduce short-lived climate pollutants, and stabilize the warming well below 2 °C both in the near term (before 2050) and in the long term (after 2050). The solutions include an atmospheric carbon extraction lever to remove CO2 from the air. The amount of CO2 that must be removed ranges from negligible (if the emissions of CO2 from the energy system and short-lived climate pollutants have started to decrease by 2020 and carbon neutrality is achieved by 2050) to a staggering one trillion tons (if the carbon lever is not pulled and emissions of climate pollutants continue to increase until 2030).

Climate change is an urgent problem requiring urgent solutions. This report lays out urgent and practical solutions that are ready for implementation now, will deliver benefits in the next few critical decades, and places the world on a path to achieving the longterm targets of the Paris Agreement and near-term sustainable development goals. The solutions consist of four building blocks and 3 levers to implement ten scalable solutions described in this report by a team of climate scientists, policy makers, social and behavioral scientists, political scientists, legal experts, diplomats and military experts from around the world.

A report by the working group commissioned by the Pontifical Academy of Sciences.

Annual greenhouse gases emissions in 2010 were at their highest recorded level in spite of a global recession. The risk is growing that the climate system could pass tipping points that lead to abrupt and irreversible impacts on a continental scale, perhaps within decades. Successfully addressing climate change requires fast and aggressive action to reduce CO2 emissions, which are responsible for up to 55% of radiative forcing since 1750. It also requires fast and aggressive action to reduce emissions of the pollutants causing the other 45% of warming – the non-CO2 climate forcers, including hydrofluorocarbons (HFCs), black carbon, methane, and tropospheric ozone. Along with reducing CO2, reducing emissions of these non- CO2 climate forcers, which in most cases can be done using existing technologies and existing laws and institutions, can cut the rate of global warming in half for several decades and by two-thirds in the Arctic in the next 30 years. In addition, given the profoundly persistent nature of CO2, it is necessary to explore and implement “carbon-negative” strategies to drawdown existing CO2 on a timescale of decades rather than millennia, and ultimately produce a net drawdown of CO2 when sinks exceed sources.

Inclusion of HFCs under the Montreal Protocol offers a path, starting in the short term, to preserve the climate benefits already achieved by this treaty.

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.