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Despite many years of active research, aerosols are still the least certain of all known climate forcings. This seriously hinders our ability to separate the roles of aerosols and greenhouse gases in driving the past climate change, thereby precluding one from reliably projecting the future climate.
The enhanced model physics allows one to simulate the climate impacts of aerosols and clouds with unprecedented realism. More Aerosols and Climate publications. RF is defined as a change in the Earth's radiation balance due to a perturbation of anthropogenic or natural origin.. The total aerosol forcing probability density function PDF , in addition to individual aerosol components, indicating both the magnitudes and uncertainty of the effects, is shown in Figure 4a.
The wider a PDF, the larger is the uncertainty. Combining all aerosol effects blue dashed curve in Figure 4a enhances the uncertainty compared to considering only the direct aerosol effect and cloud albedo effect. Figure 4: Aerosol functions. Radiative imbalances of 0. Industrial era temperature change is taken as 0. If we assume a total aerosol RF and a current energy imbalance, we can compute the resulting climate sensitivity using Equation 1 Figure 4b. This can then be compared with the PDFs for the current aerosol RF to get an indication of the range in climate sensitivities allowed by the present knowledge red and blue lines in figure 4b.
A similar figure has previously been presented in Andreae et al. The allowed climate sensitivity ranges from about 2 to 8 Kelvin K for a doubling of CO 2 using the known industrial age warming of around 0. Albrecht, B. Aerosols, cloud microphysics, and fractional cloudiness. Science , Andreae, M. Strong present-day aerosol cooling implies a hot future. Nature , Andrews, E. Climatology of aerosol radiative properties in the free troposphere.
Atmospheric Research , Boucher, O. On summing the components of radiative forcing of climate change. Climate Dynamics 18 , Boulon, J. Observations of nucleation of new particles in a volcanic plume. Charlson, R. Perturbation of the Northern-Hemisphere radiative balance by backscattering from anthropogenic sulfate aerosols.
Tellus Series a-Dynamic Meteorology and Oceanography 43 , Ervens, B. Secondary organic aerosol formation in cloud droplets and aqueous particles aqSOA : a review of laboratory, field and model studies.
Atmospheric Chemistry and Physics 11 , Forster, P. Fullerton, D. Biomass fuel use and indoor air pollution in homes in Malawi. Occupational and Environmental Medicine 66 , Graber, E. A comprehensive and critical review. Atmospheric Chemistry and Physics 6 , Hansen, J. Soot climate forcing via snow and ice albedos. Earth's energy imbalance: Confirmation and implications.
Radiative forcing and climate response. Journal of Geophysical Research-Atmospheres , Haywood, J. The effect of anthropogenic sulfate and soot aerosol on the clear-sky planetary radiation budget.
Geophysical Research Letters 22 , Holben, B. Remote Sensing of Environment 66 , The Physical Science Basis. Isaksen, I. Atmospheric composition change: Climate-chemistry interactions. Atmospheric Environment 43 , Jacobson, M. Global direct radiative forcing due to multicomponent anthropogenic and natural aerosols. Jones, A. A climate model study of indirect radiative forcing by anthropogenic sulfate aerosols. Kanakidou, M.
Organic aerosol and global climate modelling: A review. Atmospheric Chemistry and Physics 5 , Using climate models, we estimate that aerosols have masked about 50 percent of the warming that would otherwise have been caused by greenhouse gases trapping heat near the surface of the Earth.
But they also have very big, detrimental impacts on human health, and have been implicated in health problems such as lung damage. Aerosols also affect other parts of the climate system like rainfall — reducing rain in areas like India and China where it is desperately needed for food production — and they alter patterns of wind and atmospheric circulation.
In the US, diesel vehicles are the major source of soot, and filters on exhaust pipes can help reduce the amount that they pump into the air. In terms of sulfate aerosols, which are created by sulfur dioxide given off by power plants, the US and Europe have very successfully used sulfur dioxide scrubbers in power plants to reduce these emissions over the past 20 years or so.
But we can definitely do more. By reducing aerosol soot emissions, we can buy ourselves some climate time — about 5 to 10 years — while we work on reducing emissions of greenhouse gases such as carbon dioxide CO2 in parallel.
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