The Maunder Minimum, between 1645 and 1715, when sunspots were scarce
and the winters harsh, strongly suggests a link between solar activity
and climate change. Until now there was a general consensus that solar
activity has been trending upwards over the past 300 years (since the
end of the Maunder Minimum), peaking in the late 20th century -- called
the Modern Grand Maximum by some [1].
This trend has led some to
conclude that the Sun has played a significant role in modern climate
change. However, a discrepancy between two parallel series of sunspot
number counts has been a contentious issue among scientists for some
time.
The two methods of counting the sunspot number -- the Wolf
Sunspot Number and the Group Sunspot Number [2] -- indicated
significantly different levels of solar activity before about 1885 and
also around 1945. With these discrepancies now eliminated, there is no
longer any substantial difference between the two historical records.
The
new correction of the sunspot number, called the Sunspot Number Version
2.0, led by Frédéric Clette (Director of the World Data Centre
[WDC]-SILSO), Ed Cliver (National Solar Observatory) and Leif Svalgaard
(Stanford University, California, USA), nullifies the claim that there
has been a Modern Grand Maximum.
The results, presented at the
IAU XXIX General Assembly in
Honolulu, Hawai`i, today, make it difficult to explain the observed
changes in the climate that started in the 18th century and extended
through the industrial revolution to the 20th century as being
significantly influenced by natural solar trends.
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