A drawing of the Sun made by Galileo Galilei on 23 June 1613 showing the positions and sizes of a number of sunspots. Galileo was one of the first to observe and document sunspots. Credit: The Galileo Project/M. Kornmesser
The Sunspot Number is a crucial tool used to study the solar dynamo, space weather and climate change. It has now been recalibrated and shows a consistent history of solar activity over the past few centuries. The new record has no significant long-term upward trend in solar activity since 1700, as was previously indicated.
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, peaking in the late 20th century – called the Modern Grand Maximum by some.
The 2 methods of counting the sunspot number – the Wolf Sunspot Number and the Group Sunspot Number – 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 2 historical records. The new correction of the sunspot number, called the Sunspot Number Version 2.0 nullifies the claim that there has been a Modern Grand Maximum.
The newly corrected sunspot numbers now provide a homogenous record of solar activity dating back some 400 years. Existing climate evolution models will need to be reevaluated given this entirely new picture of the long-term evolution of solar activity. This work will stimulate new studies both in solar physics (solar cycle modelling and predictions) and climatology, and can be used to unlock tens of millennia of solar records encoded in cosmogenic nuclides found in ice cores and tree rings. This could reveal more clearly the role the Sun plays in climate change over much longer timescales.
http://www.iau.org/news/pressreleases/detail/iau1508/
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