UPDATE: Lead author Ben Laken responds in comments below.
I’ve reported several times at WUWT on the galactic cosmic ray theory proposed by Henrik Svensmark which suggests that changes in the sun’s magnetic field modulate the density of Galactic Cosmic Rays (GCRs) which in turn seed cloud formation on Earth, which changes the albedo/reflectivity to affect Earth’s energy balance and hence global climate.
A new paper published today in Atmospheric Chemistry and Physics suggests that the relationship has been established.
Figure 1 below shows a correlation, read it with the top and bottom graph combined vertically.
As the authors write in the abstract:
These results provide perhaps the most compelling evidence presented thus far of a GCR-climate relationship.
Dr. Roy Spencer has mentioned that it doesn’t take much in the way of cloud cover changes to add up to the “global warming signal” that has been observed. He writes in The Great Global Warming Blunder:
The most obvious way for warming to be caused naturally is for small, natural fluctuations in the circulation patterns of the atmosphere and ocean to result in a 1% or 2% decrease in global cloud cover. Clouds are the Earth’s sunshade, and if cloud cover changes for any reason, you have global warming — or global cooling.
Well, it seems that Laken, Kniveton, and Frogley have found just such a small effect. Here’s the abstract and select passages from the paper, along with a link to the full paper:
Atmos. Chem. Phys., 10, 10941-10948, 2010
Cosmic rays linked to rapid mid-latitude cloud changes
B. A. Laken , D. R. Kniveton, and M. R. Frogley
Abstract. The effect of the Galactic Cosmic Ray (GCR) flux on Earth’s climate is highly uncertain. Using a novel sampling approach based around observing periods of significant cloud changes, a statistically robust relationship is identified between short-term GCR flux changes and the most rapid mid-latitude (60°–30° N/S) cloud decreases operating over daily timescales; this signal is verified in surface level air temperature (SLAT) reanalysis data. A General Circulation Model (GCM) experiment is used to test the causal relationship of the observed cloud changes to the detected SLAT anomalies. Results indicate that the anomalous cloud changes were responsible for producing the observed SLAT changes, implying that if there is a causal relationship between significant decreases in the rate of GCR flux (~0.79 GU, where GU denotes a change of 1% of the 11-year solar cycle amplitude in four days) and decreases in cloud cover (~1.9 CU, where CU denotes a change of 1% cloud cover in four days), an increase in SLAT (~0.05 KU, where KU denotes a temperature change of 1 K in four days) can be expected. The influence of GCRs is clearly distinguishable from changes in solar irradiance and the interplanetary magnetic field. However, the results of the GCM experiment are found to be somewhat limited by the ability of the model to successfully reproduce observed cloud cover. These results provide perhaps the most compelling evidence presented thus far of a GCR-climate relationship. From this analysis we conclude that a GCR-climate relationship is governed by both short-term GCR changes and internal atmospheric precursor conditions.
I found this portion interesting related to the figure above:
The composite sample shows a positive correlation between statistically significant cloud changes and variations in the short-term GCR flux (Fig. 1): increases in the GCR flux
occur around day −5 of the composite, and correspond to significant localised mid-latitude increases in cloud change. After this time, the GCR flux undergoes a statistically significant decrease (1.2 GU) centred on the key date of the composite; these changes correspond to widespread statistically significant decreases in cloud change (3.5 CU, 1.9 CU globallyaveraged) over mid-latitude regions.
The strong and statistically robust connection identified here between the most rapid cloud decreases over mid-latitude regions and short-term changes in the GCR flux is clearly distinguishable from the effects of solar irradiance and IMF variations. The observed anomalous changes show a strong latitudinal symmetry around the equator; alone, this pattern
gives a good indication of an external forcing agent, as
there is no known mode of internal climate variability at the
timescale of analysis, which could account for this distinctive
response. It is also important to note that these anomalous
changes are detected over regions where the quality of
satellite-based cloud retrievals is relatively robust; results of
past studies concerned with high-latitude anomalous cloud
changes have been subject to scrutiny due to a low confidence
in polar cloud retrievals (Laken and Kniveton, 2010;
Todd and Kniveton, 2001) but the same limitations do not
Although mid-latitude cloud detections are more robust
than those over high latitudes, Sun and Bradley (2002) identified
a distinctive pattern of high significance between GCRs
and the ISCCP dataset over the Atlantic Ocean that corresponded
to the METEOSAT footprint. This bias does not
appear to influence the results presented in this work: Fig. 6 shows the rates of anomalous IR-detected cloud change occurring over Atlantic, Pacific and land regions of the midlatitudes during the composite period, and a comparable pattern of cloud change is observed over all regions, indicating no significant bias is present.
This work has demonstrated the presence of a small but statistically significant influence of GCRs on Earth’s atmosphere over mid-latitude regions. This effect is present in
both ISCCP satellite data and NCEP/NCAR reanalysis data for at least the last 20 years suggesting that small fluctuations in solar activity may be linked to changes in the Earth’s atmosphere via a relationship between the GCR flux and cloud cover; such a connection may amplify small changes in solar activity. In addition, a GCR – cloud relationship may also act in conjunction with other likely solar – terrestrial relationships concerning variations in solar UV (Haigh, 1996) and total solar irradiance (Meehl et al., 2009). The climatic forcings resulting from such solar – terrestrial links may have had a significant impact on climate prior to the onset of anthropogenic warming, accounting for the presence of solar cycle relationships detectable in palaeoclimatic records (e.g.,Bond et al., 2001; Neff et al., 2001; Mauas et al., 2008).
Further detailed investigation is required to better understand GCR – atmosphere relationships. Specifically, the use of both ground-based and satellite-based cloud/atmospheric monitoring over high-resolution timescales for extended periods of time is required. In addition, information regarding potentially important microphysical properties such as aerosols, cloud droplet size, and atmospheric electricity must also be considered. Through such monitoring efforts, in addition to both computational modelling (such as that of Zhou and Tinsley, 2010) and experimental efforts (such as that of Duplissy et al., 2010) we may hope to better understand the effects described here.
It seems they have found the signal. This is a compelling finding because it now opens a pathway and roadmap on where and how to look. Expect more to come.
The full paper is here: Final Revised Paper (PDF, 2.2 MB)
h/t to The Hockey Schtick