Surface of the sun
Magnetic loops gyrate above the sun,on March 23-24, 2017. NASA photo

The Sun might emit less radiation by mid-century, giving Earth a chance to warm a bit more slowly but not halting human-induced climate change, according to a new study by Scripps Institution of Oceanography.

Our star’s cool down would be the result of what astrophysicists call a “grand minimum,” a periodic event during which the Sun’s magnetism diminishes, sunspots form infrequently, and less ultraviolet radiation makes it to the surface of Earth. This last happened in the 17th century.

A team of scientists led by research physicist Dan Lubin at Scripps has created the first estimate of how much dimmer the Sun should be when the next minimum takes place, which could be by the middle of this century.

His team’s study, “Ultraviolet Flux Decrease Under a Grand Minimum from IUE Short-wavelength Observation of Solar Analogs,” appears in the publication Astrophysical Journal Letters and was funded by the state of California.

“Now we have a benchmark from which we can perform better climate model simulations,” Lubin said. “We can therefore have a better idea of how changes in solar UV radiation affect climate change.”

Lubin and colleagues David Tytler and Carl Melis of UC San Diego’s Center for Astrophysics and Space Sciences arrived at their estimate of a grand minimum’s intensity by reviewing nearly 20 years of data gathered by the International Ultraviolet Explorer satellite mission. They compared radiation from stars that are similar to the Sun and identified those that were experiencing a grand minimum.

The reduced energy from the Sun would set into motion a sequence of events on Earth beginning with a thinning of the stratospheric ozone layer.

The cooling is not uniform. In the last grand minimum, during the 17th Century, areas of Europe chilled –the Baltic Sea froze — while Alaska and southern Greenland warmed correspondingly.

Lubin said that an upcoming grand minimum would not stop the current trend of planetary warming but might slow it somewhat. That’s because the cooling effect of a grand minimum is only a fraction of the warming effect caused by the increasing concentration of carbon dioxide in the atmosphere.

Lubin’s team predicts a significant probability of a grand minimum in this century because the downward sunspot pattern in recent solar cycles resembles the run-ups to past grand minimum events.

Chris Jennewein is Editor & Publisher of Times of San Diego.