A fair and progressive carbon price for a sustainable economy.

The principle of "common but differentiated responsibility", as a key concept of the United Nations Framework Convention on Climate Change (UNFCCC), acknowledges the conditions for a generally acceptable and differentiated pricing mechanism on carbon emissions. With reference to this principle, carbon price determination has become a necessary instrument for sustainable policies. Considering the development gaps and the historical responsibility of the OECD's countries, a single carbon price would raise a major issue of equity between "developed" and "developing" countries. Although from a climate perspective each molecule of CO2 produces the same level of damage despite the nature or the location of the activity generating the emissions, all CO2 emissions are not on an equal footing. Indeed, some are necessary to improve the lives of people in "developing" countries when others can be considered not indispensable, especially beyond a certain level of development. In this policy paper, we explain how the price of carbon should be fixed according to a reference price depending on the Human Development Index (HDI) and CO2 emissions per capita. The HDI criterion enables to integrate progressivity into taxation while distinguishing what is essential from what is not. By taking a reference price based on the HDI, countries with low HDIs should pay a lower carbon price. However, with same HDI levels, countries with higher CO2 emissions should pay a penalty on the reference price. Our policy paper analyses the benefits of a differentiated and progressive carbon pricing mechanism to facilitate intergovernmental cooperation for a more sustainable economy.

Changing boreal methane sources and constant biomass burning during the last termination.

Past atmospheric methane concentrations show strong fluctuations in parallel to rapid glacial climate changes in the Northern Hemisphere superimposed on a glacial-interglacial doubling of methane concentrations. The processes driving the observed fluctuations remain uncertain but can be constrained using methane isotopic information from ice cores. Here we present an ice core record of carbon isotopic ratios in methane over the entire last glacial-interglacial transition. Our data show that the carbon in atmospheric methane was isotopically much heavier in cold climate periods. With the help of a box model constrained by the present data and previously published results, we are able to estimate the magnitude of past individual methane emission sources and the atmospheric lifetime of methane. We find that methane emissions due to biomass burning were about 45 Tg methane per year, and that these remained roughly constant throughout the glacial termination. The atmospheric lifetime of methane is reduced during cold climate periods. We also show that boreal wetlands are an important source of methane during warm events, but their methane emissions are essentially shut down during cold climate conditions.