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Variations in North Atlantic Surface Pressure
Reference
Veretenenko, S.V., Dergachev, V.A. and Dmitriyev, P.B.  2005.  Long-term variations of the surface pressure in the North Atlantic and possible association with solar activity and galactic cosmic rays.  Advances in Space Research 35: 484-490.

What was done
In the past few years researchers have begun to explore the relationship between solar activity, galactic cosmic rays and earth's climate in much greater detail, and we have reviewed a number of such studies in the Extraterrestrial Climatic Effects section of our website.  Continuing along the lines of these earlier works, Veretenenko et al. examine the potential influence of galactic cosmic rays (GCR) on the long-term variation of North Atlantic sea level pressure over the period 1874-1995.

What was learned
Comparisons of long-term variations in cold-season (October-March) sea level pressure with different solar/geophysical indices revealed that increasing sea level pressure coincided with a secular rise in solar/geomagnetic activity that was accompanied by a decrease in GCR intensity, whereas long-term decreases in sea level pressure were observed during periods of decreasing solar activity and rising GCR flux.  Spectral analysis further supported a link between sea level pressure, solar/geomagnetic activity and GCR flux, as similar spectral characteristics (periodicities) were present among all data sets at time scales from approximately 10 to 100 years.

What it means
The results of the authors' analysis support a link between long-term variations in cyclonic activity and trends in solar activity/GCR flux in the extratropical latitudes of the North Atlantic.  Concerning how this relationship works, the authors hypothesize that GCR-induced changes in cloudiness alter long-term variations in solar and terrestrial radiation receipt in this region, which in turn alters tropospheric temperature gradients and produces conditions more favorable for cyclone formation and development.

Although we are still far from a complete understanding of many solar/GCR-induced climatic influences, this study highlights the ever-growing need for such relationships to continue to be explored.  As this study and others have shown, small changes in solar output can indeed induce significant changes in earth's climate.  The empirical evidence for such phenomena continues to mount (see Solar Effects and Extraterrestrial Climate Effects in our Subject Index), and climate modelers should be paying more attention to them and incorporating them into their general circulation models of the atmosphere; for it could well be that much, if not most, of the warming of the 20th century had its origins in solar variability and not the historical rise in the air's CO2 concentration.

Reviewed 28 December 2005