July 1, 2015, revives 405-year sunspot record

Transformation to revolutionize understanding of the sun's roll in long-term climate studies

The bottom two black spots on the sun, known as sunspots, appeared quickly over the course of Feb. 19-20, 2013 | Image NASA.gov
The bottom two black spots on the sun, known as sunspots, appeared quickly over the course of Feb. 19-20, 2013 | Image NASA.gov

AUSTIN, Texas, July 8, 2015 – The longest continuously monitored daily measurement in all of science, the 405-year solar sunspot record, underwent a complete overhaul for the first time since it was created by Swiss astronomer Rudolf Wolf in 1849. The overhaul went into effect July 1.

For the very first time, the sunspot record is properly calibrated to bring internal consistency over its entire 405-year history, dating back to Galileo and the invention of the telescope. Yet this important change to one of science’s most fundamental measurements went literally unnoticed.

The newly calibrated record has implications in many diverse scientific disciplines, ranging from climate science to manned spaceflight.

Sunspots 2015: Year of the decline

It’s been known for decades there are inconsistencies in the sunspot record.

Forty of the world’s top solar physicists spent the last four years researching the problem. Their work was conducted in a series of meetings modestly called the “SSN Workshops.” Their results were published in an historic paper titled “Revisiting the Sunspot Number: A 400-Year Perspective on the Solar Cycle” – Frederic Clette, et al., Space Science Reviews, Vol. 186, Issue 1, pp. 35-103.

Hundreds of papers written over the last 166 years are directly affected by the changes. Conclusions will have to be revisited, and some will be invalidated completely. Ultimately, though, it’ll lead to a better understanding of how subtle changes on the sun are affecting life as we know it here on Earth.

Group Number: The Better Measure of Solar Activity

Two sunspot record time series were recalibrated. The first is the traditional International Sunspot Number (ISN) record most people are familiar with. The second is the more physically meaningful group number first documented by Douglas Hoyt and Kenneth Schatten in 1998.

Groups have always been counted as part of the International Sunspot Number (ISN). Hoyt and Schatten, recognizing their special nature, separated them out into their own time series then reconstructed it back to 1610. The newly released group number update redefines and corrects defects in the original 1998 version.

The group number is important for three reasons:

  1. It’s easier and more accurate counting groups than counting individual sunspots
  2. The group number series can reliably be extended further back in time
  3. Most solar activity is associated with groups, not individual spots
Group number time series best illustrates sunspot record changes. (Credit/Steve Davidson, WDC/SILSO data)
Group number time series best illustrates sunspot record changes. (Credit/Steve Davidson, WDC/SILSO data)

Individual spot and group count changes include:

  • All ISN counts increased (Wolf baseline replaced with Wolfer baseline)
  • Counts after 1947 are reduced 18 percent (count correction)
  • The old and new records match between 1890 and 1946 (Wolfer baseline)
  • Counts prior to 1890 increased (count correction, new data)
  • 405-year history has solar activity minimums every 100 years or so
  • 405-year history generally more homogeneous
New group number sunspot time series. (Credit/Steve Davidson, WDC/SILSO data)
New group number sunspot record more accurate. (Credit/Steve Davidson, WDC/SILSO data)

The newly rebuilt group number time series shows that solar activity is considerably more “even” over its 405-year history than previously thought. Formerly, it looked as if sunspot activity in the past was much weaker than at present, especially prior to 1890. Counting inconsistencies artificially created that non-existent effect.

Sunspots and climate change

The rebuilt record contains four distinctive dips in solar activity that occur roughly every 100 years. It’s not a foregone conclusion that the “Eddy Minimum” (proposed name) will actually come to pass; it’s still too early to tell for sure, but virtually all major solar activity indicators suggest it will.

Climate Change Implications

For human-caused global warming skeptics the most disappointing outcome of the revision is that the so-called “Modern Maximum” peaking in the mid-1950s largely disappears. It had been credited with some of the late 20th century warming attributed entirely to CO2 emissions by human-caused global warming theorists.

Solar activity after 1975 declined while Earth’s temperature rose sharply. Obviously, solar activity since 1975 does not correlate to Earth’s late 20th century warming. Thus, it cannot be a primary driver of Earth’s short- term temperature rise.

However, that’s not the end of the story. The “unnamed minimum” in the late 1880s to 1915 matches Earth’s temperature decline back then. After that, both solar activity and temperature increased together.

The International Panel on Climate Change (IPCC) only documents direct global temperature measurements back to 1850. Both the Dalton and Maunder minimums, and an earlier one called the Spörer Minimum, occurred before 1850. As happened between 1880 and 1915, anecdotal data suggests Earth was colder during those minimums, which is commonly referred to as “The Little Ice Age.”

Thus, periodic decades-long solar activity changes probably do have climate change effects.

If the Eddy Minimum fully develops over the next couple decades, as many solar physicists believe, then decreased solar activity will likely dampen or possibly reverse already stalled global warming by mid-century, despite increased human emissions of carbon dioxide.

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