2010-09-27 17:58:49New paper suggesting connection between cosmic rays and cloud formation
John Cook


Erik Svensson, an atmospheric scientist from Sweden who I've just invited to join us on the Authors Forum, has pointed me to a new paper Cosmic rays linked to rapid mid-latitude cloud changes (Laken et al 2010). Here's a link to the full paper. Abstract below with my own emphasis added:

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 the rate of GCR flux 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 experiment is used to test the causal relationship of the observed cloud changes to the detected SLAT anomalies. Results indicate that the cloud anomalies were responsible for producing the observed SLAT changes, implying a link between significant decreases in the rate of GCR flux (~0.79%/day (relative to the peak-to-peak amplitude of 11-yr solar cycle)), decreases in cloud cover (~1.9%/day) and increases in SLAT (~0.05 K/day). The influence of GCRs is clearly distinguishable from changes in solar irradiance and the interplanetary magnetic field. These results provide the most compelling evidence presented thus far of a GCR-climate relationship. From this analysis we conclude: (i) a GCR-climate relationship is governed by both the rate of GCR flux and internal precursor conditions; and (ii) it is likely that this natural forcing has not contributed significantly to recent anthropogenic temperature rises.

Discuss :-)

2010-09-27 18:06:39Excerpt from paper
John Cook


Reading through the paper now. Concluding paragraph:

Further investigation is needed to fully quantify the impacts of GCR variations on climate. However, based on this work, we tentatively estimate that the SLAT (surface level air temperature) change resulting from a GCR-climate relationship over the last 50 years to be approximately +0.03 K. This result strongly implies that GCR-related natural forcings are not able to account for recent anthropogenic climate trends

Haven't read to the detail to find out why this found a GCR-cloud connection where other studies failed. Would be good to do a post on this sooner than later as I can see skeptic blogs trumpeting the GCR-cloud connection found in this study (while exercising cognitive dissonance to reject the concluding paragraph).

2010-09-27 18:32:50



I guess the question would be, What limit was placed on a possible GCR-cloud connection by previous studies? You could never have said that there was NO connection, just that it was not big enough (or not correlated properly) as to support the hypothesis of causality.

Example: There are gravitational tidal effects from the jumping of fleas in New York City that propagate to Sydney. But they're very tiny.

2010-09-27 18:47:54Quick look at the paper


I notice in the description of the methodology:

"An 11-yr running mean is applied to the data and the difference between 1953 and 2006 is taken as an estimate of the long-term impact of GCR on global SLAT. Although this procedure provides an interesting estimate, it has several non-trivial caveats: it assumes a linear trend; it ignores long-term cloud changes resulting from natural climate variations such as El Niño and anthropogenic warming; the estimated value is based on the composite sample presented in this work, wherein, it is likely that the GCR flux may have been acting to enhance natural variability; it ignores the existence of feedbacks; and the estimate assumes that no other GCR – climate links exist other than those outlined in this work."

So the way they detect this effect is to subtract out AGW effects anyway. So it would hardly be in a position to challenge the assumption, even if the detected signal were larger.


2010-09-27 20:57:11


A few thoughts afetr a first (rapid) read.
The main point, in my opinion, is that the GCR-climate link is not with the GCR flux but with the rate of change of the flux. This would explain why people failed to detect the effect consistently and also why it may cause spurious detections.
Quite huge rates of change (something like twice the 11 years change in just a day or so) are required to detect the effect and the importance of pre-existent atmospheric condition (narrow latitude band, Bénard cells, etc.) is highlighted.
There are a lot of caveats clearly stated in the paper itself. I can't wait for more studies :)

Note, it's still at the discussion stage. We should wait for the final version.