Lending at least some plausibility to these hypothesis was the scientific consensus that the solar activity has been trending upwards in the 300 years since the Maunder Minimum that occurred between 1645 and 1715, when there was little sunspot activity. That has led some to argue that the Sun, rather than the burning of fossil fuels, has been the main driver of rising global temperatures.
But deniers will have a tougher time making the case now. The solar explanation for global warming is refuted by a new study just presented at the International Astronomical Union’s annual assembly in Hawaii, which fixes a discrepancy among historical records of sunspots.
The apparent upward trend of solar activity between the 18th century and the late 20th century has now been identified as a major calibration error in the Group Sunspot Number, one of the two systems for counting sunspot activity historically. (The other is the Wolf Sunspot Number.)
But now that the error has been fixed, scientists say that solar activity actually has remained relatively stable since the 1700s. That means that although fluctuations in solar weather can influence climate over shorter periods, the long-term trend is being caused by something else.
The Wolf system, which was developed back in 1856, is the oldest time series in solar terrestrial physics that’s still in use today. It counts both individual sunspots and sunspot groups. But in the mid-1990s, scientists began to question whether it was an accurate way to reconstruct the longer history of solar activity. In 1998, the Group Sunspot Number, a new index, was established. It was based in part based on sunspot measurements made by Galileo in 1612.
Read more at Discovery News
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