Even global warming as small as 2°C, sometimes called a safe guardrail, may have large effects. Bell curve shifts shown for 2005-2015 result from global warming of ~0.6°C relative to 1951-80. Thus 2°C warming relative to pre-industrial (1.7°C relative to 1951-1980) will result in bell curve shifts and climate impacts about three times greater than those that have occurred already. Global warming of 2°C is expected to cause sea level rise of several meters, leading to inference that the potential sea level rise this century is dangerous.
The overall message that climate science delivers to society, policymakers, and the public alike is this: we have a global emergency. Fossil fuel CO2 emissions should be reduced as rapidly as practical. We argue that country-by-country goals, the approach of the 21st Conference of the Parties cannot lead to rapid phase down of fossil fuel emissions, as long as fossil fuels are allowed to be the cheapest energy. It will be necessary to include a carbon fee that allows the external costs of fossil fuels to be incorporated in their price. Border duties on products from countries without a carbon fee, would lead to most nations adopting a carbon fee.
In view of the disparity between developed country and developing country emissions, there is a recognized obligation of assistance from developed countries. Developing countries have strong leverage to achieve that assistance, because their cooperation in improved agricultural and forestry practices is needed to store more carbon in the soil and biosphere and to limit trace gas emissions. In addition, international cooperation in generating more affordable carbon-free energies is needed, because otherwise economic development in many nations will continue to be based on fossil fuels, despite pollution and climate impacts.
Read more on the science at Regional Climate Change and National Responsibilities - James Hansen and Makiko Sato
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