Here is a roundup on the current IPCC thinking on cosmic rays and recent warming.
IPCC and Solar Correlations from ClimateAudit reviews the dismissal of a solar influence on climate in IPCC 1992, 1994 and 2001.
IPCC relied to some extent on MBH98 in dismissing these supposed relationships, but, given the defects in this specific area of MBH98 (as well as more general problems), alternative grounds for dismissal have to be sought if one repudiates MBH98. I’m not saying that such alternative grounds are not possible – merely that it is not prudent to rely on MBH98 in respect to taking a position on solar correlations. The other large issue is whether there are physical reasons why the efficacy of solar forcing (high-energy low-entropy at surface) might differ from the efficacy of additional CO2 forcing (low-energy high-entropy at altitude).
Evidence of cosmic rays causing decreased cloudiness and increased temperatures has continued to accumulate since 2001. For example, cores of levels of the cosmogenic isotope 10Be, a product of particle collisions with atmospheric nitrogen and oxygen, show high correlations, as shown on Anthony Watt’s in guest post by David Archibald Beryllium 10 and climate.
Instead of wading through hundreds of papers for evidence of the Sunâ€™s influence on terrestrial climate, all you have to do is look at this graph.
Further, Anthony posts that Cosmic Ray Flux and Neutron monitors suggest we may not have hit solar minimum yet and shows neutron flux has been increasing over at least the last year, and should continue suggesting colder weather to come.
What does the latest IPCC report say about cosmic rays? Working Group 1. the Physical Science Basis of Climate Change, Chapter 2: Changes in Atmospheric Constituents and in Radiative Forcing contains the discussion. The often repeated position is:
Whether solar wind fluctuations (Boberg and Lundstedt, 2002) or solar-induced heliospheric modulation of galactic cosmic rays (Marsh and Svensmark, 2000b) also contribute indirect forcings remains ambiguous.
The entire IPCC review is here, concluding the level of scientific understanding of cosmic ray influences is considered to be very low.
Many empirical associations have been reported between
globally averaged low-level cloud cover and cosmic ray
fl uxes (e.g., Marsh and Svensmark, 2000a,b). Hypothesised
to result from changing ionization of the atmosphere from
solar-modulated cosmic ray fl uxes, an empirical association
of cloud cover variations during 1984 to 1990 and the solar
cycle remains controversial because of uncertainties about the
reality of the decadal signal itself, the phasing or anti-phasing
with solar activity, and its separate dependence for low, middle
and high clouds. In particular, the cosmic ray time series
does not correspond to global total cloud cover after 1991 or
to global low-level cloud cover after 1994 (KristjÃ¡nsson and
Kristiansen, 2000; Sun and Bradley, 2002) without unproven
de-trending (Usoskin et al., 2004). Furthermore, the correlation
is significant with low-level cloud cover based only on infrared
(not visible) detection. Nor do multi-decadal (1952 to 1997)
time series of cloud cover from ship synoptic reports exhibit a
relationship to cosmic ray flux. However, there appears to be a
small but statistically signifi cant positive correlation between
cloud over the UK and galactic cosmic ray fl ux during 1951 to
2000 (Harrison and Stephenson, 2006). Contrarily, cloud cover
anomalies from 1900 to 1987 over the USA do have a signal
at 11 years that is anti-phased with the galactic cosmic ray
fl ux (Udelhofen and Cess, 2001). Because the mechanisms are
uncertain, the apparent relationship between solar variability
and cloud cover has been interpreted to result not only from
changing cosmic ray fl uxes modulated by solar activity in the
heliosphere (Usoskin et al., 2004) and solar-induced changes in
ozone (Udelhofen and Cess, 2001), but also from sea surface
temperatures altered directly by changing total solar irradiance
(KristjÃ¡nsson et al., 2002) and by internal variability due to
the El NiÃ±o-Southern Oscillation (Kernthaler et al., 1999). In
reality, different direct and indirect physical processes (such as
those described in Section 9.2) may operate simultaneously.
The direct RF due to increase in solar irradiance is reduced
from the TAR. The best estimate is +0.12 W mâ€“2 (90%
confi dence interval: +0.06 to +0.30 W mâ€“2). While there have
been advances in the direct solar irradiance variation, there
remain large uncertainties. The level of scientifi c understanding
is elevated to low relative to TAR for solar forcing due to direct
irradiance change, while declared as very low for cosmic ray
infl uences (Section 2.9, Table 2.11).
However, there is a much more abundant literature not discussed, as shown in the quote by David Archibald on Anthony’s blog. As of 2007, cosmic rays do not rate a mention in the Summary for Policymakers. The report mentions lack of knowledge of the strength of possible mechanisms repeatedly. It restricts its references to a few of the most prominent. Even in the latest report, despite the burgeoning of results and data, they have not seriously considered cosmic rays as a possible cause of recent warming.
A high rigor process ensures that all important processes have been seriously considered, before making strong claims. To prematurely settle on one factor, and reject another that is highly promising, simply because its not well understood or abundantly researched, is referred to as ‘looking for lost keys under the streetlight’ (because that’s where the light is).
Given the largest uncertainty in climate change is the effect of clouds, cosmic rays have always had the potential to overturn the IPCC claims that carbon emissions are a big problem. When the shock of the revelation that CO2 has little or nothing to do with warming turns to disgust, people will justifiably ask who got us into this mess. The answer, in part, is the UN sponsored IPCC.
How do you describe the dismissal of a solar connection on the basis of a single, now discredited hockey-stick study; dismissal of an emerging picture as ambiguous, and dismissal of a large, accessible, peer-reviewed literature as very low understanding? ‘Asinine‘ sounds like a good word.