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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.