A newly updated analysis of sunspot numbers over the last 400 years suggests solar activity has nothing to do with climate change, a discovery that eliminates a key argument used by those who question human caused climate change.
Some of those who suggest that climate change is not anthropogenic in nature contend that changes in the sun’s activity are responsible for any increase or decrease in global temperatures.
Scientists have been tracking that solar activity within the sun’s solar cycle by counting sunspots for years.
For the last 160 years scientists have relied on the Wolf Sunspot Number (WSN) – also called the International sunspot number, relative sunspot number, or Zürich number – to count the number of sunspots present on the surface of the sun.
Use of the WSN, since its introduction by Rudolph Wolf in 1856, has allowed scientists to develop a historical record of solar activity over time.
But in 1994 scientists began to question whether the WSN was an accurate method to build a reliable index of historical sunspot records.
Since telescope technology before modern times wasn’t as advanced as today the scientists thought that perhaps some smaller sunspots were being missed in the count.
So, a new counting method called the Group Sunspot Number (GSN) was created by Douglas Hoyt and Ken Schatten in 1994 and introduced in 1998.
Creators of this new way of counting sunspots said that they were able to add to amount of available sunspot data since it included measurements made further back into the sunspot historical record by Galileo, Thomas Harriot and Christoph Scheiner.
However there are huge discrepancies between the WSN and GSN for sunspot measurements made before 1885 and around 1945. This has become a contentious issue among scientists for some time.
One of the links between solar activity and climate change that’s often cited by the non-believers of human caused climate change is a time period called the Maunder Minimum.
During the Maunder Minimum, which took place between 1645 and 1715, scientists noticed fewer sunspots on the sun’s surface. Winters throughout this time were also unusually harsh.
Some scientists have said that following the end of the Maunder Minimum, which was also the beginning of the industrial revolution, a new period of increased solar activity began.
This period of increased solar activity, which is said to have peaked in the late 20th century with the Modern Grand Maximum, also happened to coincide with a rise in global temperatures.
While the GSN index reflected this pattern of increased solar activity the WSN didn’t show such a pattern.
A group of scientists led by Frédéric Clette, Director of the Sunspot Index and Long-term Solar Observations program at the World Data Center, Ed Cliver from the National Solar Observatory and Leif Svalgaard of Stanford University have found that the discrepancies between the WSN and GSN were due to a major calibration error in the Group Sunspot Number.
So scientists reconciled and recalibrated the sunspot index which has eliminated the discrepancies between the WSN and GSN.
The resulting new sunspot index called the Sunspot Number Version 2.0, which also includes the older historical data of the GSN, shows that solar activity has been constant over the past few centuries without any noteworthy long-term upward trends in solar activity since 1700.
This means that any rise in global temperatures since the beginning of the industrial revolution or end of the Maunder Minimum cannot be attributed to an increase in solar activity.
The scientists presented their new sunspot index at the International Astronomical Union’s 29th General Assembly being held in Honolulu, Hawaii through August 14th.