An incremental step blown up

We see the same thing in a study by Harrison & Stephenson (2006), which provides an additional clue based on diffuse light, which is light scattered by clouds. They do find a link between cosmic galactic rays (GCR) and the diffuse light (figure below), suggesting a link between the GCR and cloudiness. But when you look at the scatter plot, the link is not very visible (if you ignore the fitted lines). The reason for this is that this link is very weak.

Figure 3. Scatter plot of the daily mean diffuse light fraction measured in Jersey (y-axis) plotted against Climax daily average neutron count rate (x-axis). Reproduction of Harrison & Stephenson (2006), Fig. 2a.

There has been a number of studies on the relationship between solar activity and earth’s climate, suggesting there is a solar signal. But the solar influence seems to be weak. GCR don’t come from the sun, but are charged particles from distant galaxies and stars that are modulated by the solar magnetic field. The solar magnetic field is closely linked to solar activity.

Figure 1 here may be consistent with a weak relationship between GCR and clouds, due to a substantial scatter, weak trend (not very steep slope), and the pronounced effect of changing the air supply.

It is conceivable that turbulent mixing of the air will produce small pockets of air with higher formation rates, in a same fashion as air with different impurities did in the experiments of Enghoff et al.

However, there is another reason why there really is a weak link from Enghoff et al.’s results to clouds. The experiment conducted by Enghoff et al. examined the formation of ultra-fine aerosols with size of 4 nanometers. But clouds need particles of the size approximately 10000 nanometers (10 micrometers) to form cloud drops for air that is barely supersaturated, according to the Köhler curve (which is central to cloud micro-physics).

What happens between the stage where 4nm aerosols form and the stage where they becomeact as CCNcloud drops (with a ~10 micrometer radius) is unknown (see Figure 4 for a depiction of these two stages). The aerosols must grow and become an order of million times larger in terms of their initial volume.

Figure 4. Comparison between ultra-fine aerosols with 4 nm radius (red) and cloud drop with 10 micrometer radius (blue). The ultra-fine aerosol is almost invisible compared to the cloud drop on the left, so a blown up version is shown on the right.

It is interesting to note the way the word “climate” appears in the GRL paper (3 times: once in the introduction and twice in the titles in the reference list) and the Danish press release (15 times, counting phrases such as ‘climate chamber’ and ‘climate researcher’). The press release claims that the results

substantiate the connection between the Sun’s magnetic activity and the Earth’s climate

and that

there is much to indicate that climate models must hereby take cosmic radiation into consideration.

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