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2002 .

(2 publications)

J.-L. Dufresne, C. Gautier, P. Ricchiazzi, and Y. Fouquart. Longwave Scattering Effects of Mineral Aerosols. Journal of Atmospheric Sciences, 59:1959-1966, June 2002. [ bib | DOI | ADS link ]

Scattering in the longwave domain has been neglected in the first generation of radiative codes and is still neglected in most current GCMs. Scattering in the longwave domain does not play any significant role for clear-sky conditions but recent works have shown that it is not negligible for cloudy conditions. This paper highlights the importance of scattering by mineral aerosols in the longwave domain for a wide range of conditions commonly encountered during dust events. The authors show that neglecting scattering may lead to an underestimate of longwave aerosol forcing. This underestimate may reach 50% of the longwave forcing at the top of atmosphere and 15% at the surface for aerosol effective radius greater than a few tenths of a micron. For an aerosol optical thickness of one and for typical atmospheric conditions, the longwave forcing at the top of the atmosphere increases to 8 W m2 when scattering effects are included. In contrast, the heating rate inside the atmosphere is only slightly affected by aerosol scattering: neglecting it leads to an underestimate by no more than 10% of the cooling caused by aerosols.

J.-L. Dufresne, L. Fairhead, H. Le Treut, M. Berthelot, L. Bopp, P. Ciais, P. Friedlingstein, and P. Monfray. On the magnitude of positive feedback between future climate change and the carbon cycle. Geophysical Research Letters, 29:1405, May 2002. [ bib | DOI | ADS link ]

We use an ocean-atmosphere general circulation model coupled to land and ocean carbon models to simulate the evolution of climate and atmospheric CO2 from 1860 to 2100. Our model reproduces the observed global mean temperature changes and the growth rate of atmospheric CO2 for the period 1860-2000. For the future, we simulate that the climate change due to CO2 increase will reduce the land carbon uptake, leaving a larger fraction of anthropogenic CO2 in the atmosphere. By 2100, we estimate that atmospheric CO2 will be 18% higher due to the climate change impact on the carbon cycle. Such a positive feedback has also been found by Cox et al. [2000]. However, the amplitude of our feedback is three times smaller than the one they simulated. We show that the partitioning between carbon stored in the living biomass or in the soil, and their respective sensitivity to increased CO2 and climate change largely explain this discrepancy.

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