Correction to the Sunspot Number – the longest scientific experiment and a crucial tool for study of solar dynamo, space weather and climate change – has effectively questioned the role of sunspots in climate change.
The Sunspot number has been recalibrated and based on the updated data there seems to be no significant long-term upward trend in solar activity since 1700, as was previously indicated, thereby suggesting that previous theories that linked rising global temperatures since the industrial revolution to increased solar activity may need re-evaluation as there is no plausible link between the two.
The findings based on the analysis and the implications of the results on climate research were revealed during a press briefing at the International Astronomical Union (IAU) XXIX General Assembly held in in Honolulu, Hawai`i, USA.
Researchers have long believed that the Maunder Minimum, which was recorded between 1645 and 1715, provides a proof of a link between solar activity and climate change. During the Maunder Minimum there were scarce sunspots and the winters harsh. This led climate scientists to believe that there is a direct connection between the two.
Further, there has been a general consensus that solar activity has been trending upwards over the course of last 300 years (since the end of the Maunder Minimum) and it peaked in the late 20th century. This peak is referred to as the Modern Grand Maximum by some. This has led many to believe that Sun has played a significant role in modern climate change.
However, there has been another issue that has been bothering scientists for quite a long time. The discrepancy between two parallel series of sunspot number counts – the Wolf Sunspot Number and the Group Sunspot Number – suggested that there have been significantly different levels of solar activity before about 1885 and also around 1945.
These discrepancies have now been eliminated and researchers say that there is no 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.
In the updated Sunspot Number, the apparent upward trend of solar activity between the 18th century and the late 20th century has been identified as a major calibration error and with this error corrected, solar activity appears to have remained relatively stable since the 1700s effectively raising questions on the role of solar activity in climate change.
The new sunspot numbers now provide a homogenous record of solar activity dating back some 400 years. Climate scientists would need to reevaluate climate evolution and climate change models keeping in mind the new sunspot numbers well as the entirely new picture of the long-term evolution of solar activity.