More cloud uncertainties: researching the effect of aerosol particles on clouds and the climate

Again it turns out that climate modellers don’t understand cloud effects too well. As this article bluntly puts it: ‘The interactions of atmospheric aerosols with solar radiation and clouds continue to be inadequately understood and are among the greatest uncertainties in the model description and forecasting of changes to the climate. One reason for this is the many unanswered questions about the hygroscopicity of aerosol particles.’ — Other reasons aren’t discussed here. Why do we keep reading about ‘state-of-the-art’ climate models when they clearly have a long way to go to merit such a description? Any forecasts they produce should be treated with great caution, to say the least.
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The extent to which aerosol particles affect the climate depends on how much water the particles can hold in the atmosphere, says Phys.org.

The capacity to hold water is referred to as hygroscopicity (K) and, in turn, depends on further factors—particularly the size and chemical composition of the particles, which can be extremely variable and complex.

Through extensive investigations, an international research team under the leadership of the Max Planck Institute for Chemistry (MPIC) and the Leibniz Institute for Tropospheric Research (TROPOS) was able to reduce the relationship between the chemical composition and the hygroscopicity of aerosol particles to a simple linear formula.

In a study published in the journal Nature Communications, they showed that hygroscopicity averaged globally, is essentially determined by the share of organic and inorganic materials making up the aerosol.

The hygroscopicity of aerosol particles is an important factor in the effect of aerosol particles on the climate and, thus, also for forecasting changes to the climate using global climate models.

“The capacity to hold water depends on the composition of aerosol particles, which can vary considerably in the atmosphere. However, in our study, we were able to show that simplified assumptions can be made for the consideration of hygroscopicity in climate models,” explains Mira Pöhlker.

She is in charge of the “Atmospheric Microphysics” department at TROPOS and is a professor at the University of Leipzig. According to the aerosol and cloud researcher, this is the first study to use measurement results from across the world to show that a simple linear formula can be used without creating huge uncertainty in climate models.
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The interactions of atmospheric aerosols with solar radiation and clouds continue to be inadequately understood and are among the greatest uncertainties in the model description and forecasting of changes to the climate. [Talkshop comment – worth reading that sentence again.] One reason for this is the many unanswered questions about the hygroscopicity of aerosol particles.

Depending on size and chemical composition, tiny aerosol particles can hold different amounts of water. This is important both for the scattering of solar radiation by the aerosol particles themselves as well as for the formation of cloud droplets. Particles that hold more water scatter more sunlight back into the universe and can also have a cooling effect through the formation of more cloud droplets.

Full article here.