Scientific Case for Avoiding Dangerous Climate Change to Protect Young People and Nature

by James Hansen^a,1,2,3, Pushker Kharecha^a, Makiko Sato^a, Frank Ackerman^b, Paul J. Hearty^c,Ove Hoegh-Guldberg^d, Shi-Ling Hsu^e, Fred Krueger^f, Camille Parmesan^g, Stefan Rahmstorf^h, Johan Rockstromⁱ, Eelco J. Rohling^j, Jeffrey Sachs^k, Pete Smith^l, Konrad Steffen^m, Lise Van Susterenⁿ, Karina von Schuckmann^o, James C. Zachos^p

Summary. Humanity is now the dominant force driving changes of Earth's atmospheric composition and thus future climate (1). The principal climate forcing is carbon dioxide (CO2) from fossil fuel emissions, much of which will remain in the atmosphere for millennia (1, 2). The climate response to this forcing and society's response to climate change are complicated by the system's inertia, mainly due to the ocean and the ice sheets on Greenland and Antarctica. This inertia causes climate to appear to respond slowly to this human-made forcing, but further long-lasting responses may be locked in. We use Earth’s measured energy imbalance and paleoclimate data, along with simple, accurate representations of the global carbon cycle and temperature, to define emission reductions needed to stabilize climate and avoid potentially disastrous impacts on young people, future generations, and nature. We find that global CO2 emissions reduction of about 6%/year is needed, along with massive reforestation.

Governments have recognized the need to limit emissions to avoid dangerous human made climate change, as formalized in the Framework Convention on Climate Change (3), but only a few nations have made substantial progress in reducing emissions. Continued...

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