Responsable : Laurent Bopp, LSCE 

Objectifs et stratégie

The future evolution of the Earth’s radiative forcing will depend upon anthropogenic activities, reflecting economic development pathways and the structure of energy production systems, as well as the response of natural biogeochemical cycles.

Over the past two decades, 80% of the increased radiative forcing of long lived greenhouse gases is caused by the emissions of CO2 from fossil fuel burning and land use change. This illustrates how crucial is the carbon cycle in controlling the future rate of climate change. Roughly half of the current anthropogenic CO2 emissions are absorbed by natural sinks in the ocean and in terrestrial ecosystems. But models of the coupled climate-carbon system consistently predict that future climate change will reduce the ability of natural sinks to continue to absorb anthropogenic CO2.

Like the carbon cycle, other long lived greenhouse gases with a global warming effect, CH4 and N2O, also have an anthropogenic and a natural component linked to land and ocean biogeochemistry and to atmospheric chemistry. The evolution of these two components in response to climate and atmospheric composition changes is important to quantify and understand, including the underlying processes. 

Short-lived aerosols and reactive gasesare produced by a variety of processes and transported away from emission regions. Unlike long lived greenhouse gases, these species exert a regional climate forcing, which can be either positive or negative in the case of aerosols. Locally, the climate forcing of aerosols and reactive gases can be larger in magnitude than that of greenhouse gases. Measures to improve air quality worldwide may release the ‘aerosol brake’, and foster the warming induced by greenhouse gases. Some aerosols like nitrates, ammonium, and mineral dust containing iron and phosphorus also exert a “fertilizing” effect over ocean and terrestrial ecosystems where they are deposited, generally increasing productivity. Increased productivity can result into more efficient CO2 sink, but can also yield to higher CH4 emissions by wetlands. In some instances, however, excess deposition of nitrogen will lead to decline of productivity in polluted regions, and sulfate deposition may inhibit CH4 emissions in wetlands.

The goal of WP1 is to coordinate and develop research on the evolution of atmospheric long-lived greenhouse gases, CO2, CH4, N2O and aerosols and reactive gases at IPSL, both for observations and for modelling. Specific focus will be given to interactions between aerosols and greenhouse gases, and the attribution of changes in biogeochemistry induced by aerosols, and in a second phase, by reactive gases as well.