Climate Response And Radiative Forcing From Mineral Aerosols By Mahowald Et Al 2006

Climate Science has promoted the perspective that climate forcings involve much more than just the radiative forcing from carbon dioxide. This viewpoint is also emphasized in a National Research Council report

National Research Council, 2005: Radiative forcing of climate change: Expanding the concept and addressing uncertainties. Committee on Radiative Forcing Effects on Climate Change, Climate Research Committee, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington, D.C., 208 pp.

There was a paper in 2006 that investigated one of these issues; the role of mineral aerosols as a climate forcing. The paper is

Mahowald N. M., M. Yoshioka, W. D. Collins, A. J. Conley, D. W. Fillmore, D. B. Coleman (2006), Climate response and radiative forcing from mineral aerosols during the last glacial maximum, pre-industrial, current and doubled-carbon dioxide climates, Geophys. Res. Lett., 33, L20705, doi:10.1029/2006GL026126.

The abstract reads

“Mineral aerosol impacts on climate through radiative forcing by natural dust sources are examined in the current, last glacial maximum, pre-industrial and doubled-carbon dioxide climate. Modeled globally averaged dust loadings change by +88%, +31% and −60% in the last glacial maximum, pre-industrial and future climates, respectively, relative to the current climate. Model results show globally averaged dust radiative forcing at the top of atmosphere is −1.0, −0.4 and +0.14 W/m2 for the last glacial maximum, pre-industrial and doubled-carbon dioxide climates, respectively, relative to the current climate. Globally averaged surface temperature changed by −0.85, −0.22, and +0.06 °C relative to the current climate in the last glacial maximum, pre-industrial and doubled carbon dioxide climates, respectively, due solely to the dust radiative forcing changes simulated here. These simulations only include natural dust source response to climate change, and neglect possible impacts by human land and water use.”

In the conclusions, they write

“The net instantaneous top-of-atmosphere radiative forcing differences due to dust between the last glacial maximum, pre-industrial and doubled-carbon dioxide climates and the current climate are −0.53, −0.43, and +0.14 W/m2, respectively. If we include the impact of glaciogenic sources, the net top-of-atmosphere radiative forcing difference between the last glacial maximum and the current climate increases in magnitude to −1.04 W/m2. In the future we simulate a 0.14 W/m2 increase in radiative forcing because of a reduction in dust from carbon dioxide fertilization of the vegetation. It is uncertain that the carbon dioxide fertilization effect will continue in the future, when other nutrients may become limiting….”

and

” Despite the possible sensitivity of the results to our model specifications, our results suggest some interesting relationships across the different climate studies. Radiative forcing at the top-of-atmosphere and surface is linear with aerosol optical depth, even in different climates. Climate response in surface temperature and precipitation are roughly linear with aerosol optical depth in our model, with a decrease in both surface temperature and precipitation associated with increasing optical depth. Finally, our model predicts statistically significant decreases in temperature at many latitudes (not just close to the dust sources) when dust is added in the different climates, and a shift in precipitation from the northern part of the ITCZ to the southern part of the ITCZ.”

Mineral dust is yet another climate forcing that was inadequately assessed in the 2007 IPCC report. Mineral dust has a natural component (it occurred prior to any human disturbance of the landscape), and now has a human contribution through landscape degradation as a result of deliberate and inadvertent land management practices.

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