Reply to Lockwood and Fröhlich – The persistent role of the Sun in climate forcing
Svensmark, H. and Friis-Christensen, E.
Danish National Space Center, Copenhagen, Denmark
In a recent paper (ref. ) Mike Lockwood and Claus
Frohlich have argued that recent trends in solar climate
forcing have been in the wrong direction to account for
“the observed rapid rise in global mean temperatures”.
These authors accept that “there is considerable evidence
for solar in°uence on Earth’s pre-industrial climate and
the Sun may well have been a factor in post-industrial
climate change in the first half of the last century.” But
they argue that this historical link between the Sun and
climate came to an end about 20 years ago. Here we
rebut their argument comprehensively.
By Lockwood and Frohlich’s own data, solar magnetic
activity is still high compared with 100 years ago. As
to when the recent easing of activity began, counts of
cosmic-ray muons at low altitudes were historically low
when the muon record-keeping ended in the early 1990s
(ref. ). That implies an increase in relevant solar mag-
netic activity continuing till that time. A scarcity of
muons can be linked to elevated global temperatures by a
reduction in low cloud cover (ref. ) and low cloudiness
was indeed at a minimum around 1992-93. By other so-
lar indicators, like those cited by Lockwood and Frohlich,
the minimum muon counts may well be a little higher in
the current solar cycles. That would explain the pause in
global warming evident in our Table as well as in Lock-
wood and Frohlich’s own Fig. 1e.
That would explain the pause in global warming ev-
ident especially in the ocean (Fig. 1) and the tropo-
sphere (Fig. 3). The continuing rapid increase in carbon
dioxide concentrations during the past 10-15 years has
apparently been unable to overrule the flattening of the
temperature trend as a result of the Sun settling at a
high, but no longer increasing, level of magnetic activity.
Contrary to the argument of Lockwood and Frohlich, the
Sun still appears to be the main forcing agent in global