The sun is responsible for Earth’s ability to sustain life, and drives space weather events that can have rippling effects down near the surface.
But, when it comes to the current spike in global temperatures, experts say the sun is not to blame.
Scientists investigating the sun’s influence on the current climate have found that, over the last few decades, there has been no increase in brightness – and instead, they found a slight decrease, suggesting it has not played a role in recent warming.
When the sun’s activity dips, Earth has experienced periods of cooler temperatures. An image taken during solar maximum (2001) is shown on left, compared to solar minimum (2009) on right
THE SOLAR CYCLE
Conventional wisdom holds that solar activity swings back and forth like a simple pendulum.
At one end of the cycle, there is a quiet time with few sunspots and flares.
At the other end, solar max brings high sunspot numbers and frequent solar storms.
It’s a regular rhythm that repeats every 11 years.
Reality is more complicated.
Astronomers have been counting sunspots for centuries, and they have seen that the solar cycle is not perfectly regular.
While the sun can influence Earth’s climate, only certain wavelengths of radiation are able to make it to the surface to actually heat it up, according to an article from the Max Planck Society.
This primarily includes visible light.
In addition, the sun emits a flow of electrically charged particles.
When the sun is in a period of high magnetic activity, it produces more intense radiation – and, by tracking these fluctuations, researchers are able to determine how such activity influences Earth’s climate.
When the sun’s activity dips, Earth has experienced periods of cooler temperatures.
This was seen during the ‘Little Ice Age’ of 1645-1715, for example, when much of the world was hit with colder winters.
In the new research, Max Planck team used records of observational sunspot data as well as Carbon-14 levels in tree rings to track changes in solar activity.
This revealed that over the last few decades, as Earth has steadily warmed, the sun has not increased in brightness.
Instead, in the last 30-40 years, there has been a slight decrease.
‘This means that the sun cannot have contributed to global warming,’ according to an article from the Max Planck Society, describing the research.
‘In fact, the temperature increase noted in recent decades cannot be reproduced in models if only the influence of the sun or other natural sources are taken into account (for example volcanic eruptions.)
By tracking fluctuations in the sun’s activity, researchers are able to determine how it influences Earth’s climate. The graph above shows variations within the eleven-year solar cycle as well as short-term variations caused by individual sunspot groups and solar flares
‘Only when anthropogenic, that is human-driven, factors are incorporated in the climate data, do they agree with the observational and measured data.
The findings go against the idea that the sun’s current dip in activity will counteract the recent warming, the experts explain.
NASA recently revealed the sun is heading toward a low point known as solar minimum, expected in 2019-2020.
THE MAUNDER MINIMUM
The Maunder Minimum (also known as the prolonged sunspot minimum) is the name used for the period starting in about 1645 and continuing to about 1715 when sunspots became exceedingly rare, as noted by solar observers of the time.
It caused London’s River Thames to freeze over, and ‘frost fairs’ became popular.
Maunder Minimum (also known as the prolonged sunspot minimum) is the name used for the period starting in about 1645 and continuing to about 1715 when sunspots became exceedingly rare, as noted by solar observers of the time
This period of solar inactivity also corresponds to a climatic period called the ‘Little Ice Age’ when rivers that are normally ice-free froze and snow fields remained year-round at lower altitudes.
There is evidence that the Sun has had similar periods of inactivity in the more distant past, Nasa says.
The connection between solar activity and terrestrial climate is an area of on-going research.
The Frozen Thames, 1677 – an oil painting by Abraham Hondius shows the old London Bridge during the Maunder Minimum
Some scientists hypothesize that the dense wood used in Stradivarius instruments was caused by slow tree growth during the cooler period.
Instrument maker Antonio Stradivari was born a year before the start of the Maunder Minimum.
The change, however, doesn’t mean that activity ceases altogether, the space agency explained.
Instead, different types of events tend to take hold.
While sunspots may decrease, long-lived coronal holes and other phenomenon could become more common.