Why the sun is dimmer and cooler?
Scientist say that the sun is expected to be in a dimmer, cooler cycle in 2050. What does this mean for planet earth?
In 2050, our sun is expected to be extremely cool.
It is what scientists call a “grand minimum” — a particularly weak point in what is otherwise a steady 11-year cycle.
On this cycle, the sun’s turbulent heart races and rest.
At the highest point, the nuclear fusion in the sun’s core forces more magnetic loops high in the boiling atmosphere — the ejection of more uv-radiation and the generation of sunspots and flares.
When it’s quiet, the surface of the sun is calm. It sheds less uv radiation.
Now, scientists have scoured the skies and the history for evidence of a still larger cycle among these cycles.
A particularly cool period in the 17th century, guided their research.
An intense cold snap in between 1645 and 1715, was also known as the “Maunder Minimum”.
In England, the Thames froze over. The Baltic Sea was covered with ice, so much so that the Swedish army was able to march on to invade Denmark in 1658.
But the cooling is not uniform: Distorted weather patterns warmed, Alaska and Greenland.
These records were combined with 20 years of data collected by the International Ultraviolet Explorer satellite mission, as well as observations of nearby stars similar to the sun.
Now physicist Dan Lubin of the University of California at San Diego has calculated that an estimate of how much dimmer the sun is probably at the next grand minimum occurs.
His team’s study, “Ultraviolet Flux Decline Under a Grand Minimum of BEI Short wavelength observations of Solar Analogues,” published in the journal Astrophysical Journal Letters.
It finds the sun is likely to be 7 percent cooler than the usual minimum.
And even a grand minimum is probably just decades away, based on the cooling coil of the recent solar cycles.
A quiet sun has a noticeable effect on the planets.
For the Earth, Lubin says the first thinning of the ozone layer in the stratosphere.
This has consequences for the insulating effect of the atmosphere, with flow-on effects including significant changes to weather and wind patterns.
But it will not stop with the current trend of global warning, Lubin warns.
“The cooling effect of a grand minimum is only a fraction of the warming of the earth caused by the increasing concentration of carbon dioxide in the atmosphere,” a statement from the research team reads.
“After hundreds of thousands of years, CO2 levels never more than 300 parts per million in the air, the concentration of the greenhouse gases is now more than 400 parts per million, continuing the increase that began with the Industrial Revolution.”
A simulation of a grand minimum on the Earth’s current climate provides a reduction of the solar warming of the earth by 0.25 percent over a 50-year period between 2020 and 2070.
While the global average surface temperature of the air seems to cool “a few tenths of a degree Celsius” in the first years, this reduction was quickly overtaken by the ever-increasing trends.
“A future grand solar minimum could slow down but not stop global warming,” the study finds.
“Now we have a benchmark from which we can better perform climate model simulations,” Lubin says. “We can, therefore, have a better idea of how changes in solar UV radiation affect the climate change.”
This story was previously published in the news.com.au.