The Sun may emit less radiation by mid-century, giving Earth a chance to warm a bit slowly, though not halting human-induced climate change altogether, shows a new study by University of California, San Diego, scientists.
The cooldown will be the result of what scientists 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 the planet, says a statement issued by the UCSD News Center.
It says, “scientists believe that the event is triggered at irregular intervals by random fluctuations related to the Sun’s magnetic field. Reconstructions based on geological and historical data have been used to a cold period in Europe in the mid-17th Century to such an event, named the ‘Maunder Minimum’.”
“Temperatures were low enough to freeze the Thames River as well as the Baltic Sea,” it adds.
In the latest study, “Ultraviolet Flux Decrease Under a Grand Minimum from IUE Short-wavelength Observation of Solar Analogs”, the team of scientists led by research physicist Dan Lubin at UCSD’s Scripps Institution of Oceanography has for the first time estimated how much dimmer the Sun should be when the next minimum takes place.
The statement notes that there is a well-known 11-year cycle in which the Sun’s ultraviolet radiation peaks and declines as a result of sunspot activity. During a grand minimum, however, ultraviolet radiation diminishes an additional seven percent beyond the lowest point of the cycle, based on the UCSD team’s research findings.
“Now we have a benchmark from which we can perform better climate model simulations,” Lubin is quoted as saying in the statement. “We can therefore have a better idea of how changes in solar UV radiation affect climate change.”
Lubin and his colleagues from UCSD’s Center for Astrophysics and Space Sciences calculated 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 analogous to the Sun and identified those that were experiencing minima.
“The reduced energy from the Sun sets into motion a sequence of events on Earth beginning with a thinning of the stratospheric ozone layer. That thinning in turn changes the temperature structure of the stratosphere, which then changes the dynamics of the lower atmosphere, especially wind and weather patterns. The cooling is not uniform. While areas of Europe chilled during the Maunder Minimum, other areas such as Alaska and southern Greenland warmed correspondingly,” highlights the statement.
Despite how much the Maunder Minimum may have affected Earth the last time, Lubin says in the statement that an upcoming event will not stop the current trend of planetary warming but may slow it down somewhat. “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. After hundreds of thousands of years of CO2 levels never exceeding 300 parts per million in air, the concentration of the greenhouse gas is now over 400 parts per million, continuing a rise that began with the Industrial Revolution.”
The UCSD statement notes that computer models have been used in other studies as well to estimate what an event similar to a Maunder Minimum may mean for our rapidly warming climate in the coming decades.
One such study it quotes has looked at the climate consequences of a future Maunder Minimum-type grand solar minimum, assuming a total solar irradiance reduced by 0.25 percent over a 50-year period from 2020 to 2070. “The study finds that after the initial decrease of solar radiation in 2020, globally averaged surface air temperature cools down by up to several tenths of a degree Celsius. By the end of the simulated grand solar minimum, however, the warming in the model with the simulated Maunder Minimum nearly catches up to the reference simulation.”
The study’s conclusion is the same arrived at by the UCSD team led by Lubin, that a future grand solar minimum can slow down but not stop global warming.