The impact of changes in solar activity on Earth’s climate was up to seven times greater than climate models suggested according to new research published today in Nature Communications.
Researchers have claimed a breakthrough in understanding how cosmic rays from supernovas react with the sun to form clouds, which impact the climate on Earth.
The findings have been described as the “missing link” to help resolve a decades long controversy that has big implications for climate science.
llustration of cosmic rays interacting with the atmosphere. A proton with energy of 100 GeV interact at the top of the atmosphere and produces a cascade of secondary particles who ionize molecules when traveling through the air. One 100 GeV proton hits every m2 at the top of the atmosphere every second.
Lead author, Henrik Svensmark, from The Technical University of Denmark has long held that climate models had greatly underestimated the impact of solar activity.
He says the new research identified the feedback mechanism through which the sun’s impact on climate was varied.
Professor Svensmark’s theories on solar impact have caused a great deal of controversy within the climate science community and the latest findings are sure to provoke new outrage.
He does not dispute that increased levels of carbon dioxide in the atmosphere have a warming impact on the climate.
But his findings present a challenge to estimates of how sensitive the climate is to changes in carbon dioxide levels in the atmosphere.
Professor Svensmark says his latest findings were consistent both with the strong rise in the rate of global temperature change late last century and a slowdown in the rate of increase over the past 20 years.
‘’It gives a physical foundation to the large body of empirical evidence showing that solar activity is reflected in variations in Earth’s climate,” a media statement accompanying the scientific report said.
“For example, the Medieval Warm Period around year 1000AD and the cold period in the Little Ice Age 1300-1900 AD both fits changes in solar activity,” it said.
“Finally we have the last piece of the puzzle of why the particles from space are important for climate on Earth,” it said.
The study reveals how atmospheric ions, produced by the energetic cosmic rays raining down through the atmosphere, helps the growth and formation of cloud condensation nuclei — the seeds necessary for forming clouds in the atmosphere.
More cloud condensation nuclei mean more clouds and a colder climate, and vice versa.
“Since clouds are essential for the solar energy reaching the surface of the Earth the implications are huge for our understanding of why climate has varied in the past and also for a future climate changes,” the statement said.
Professor Svensmark said it had until now wrongly been assumed that small additional nucleated aerosols would not grow and become cloud condensation nuclei, since no mechanism was known to achieve this.
The research team tested its ideas experimentally in a large cloud chamber.
Data was taken over a period of two years with total 3100 hours of data sampling.
Professor Svensmark said the new results gave a physical foundation to the large body of empirical evidence showing that Solar activity is reflected in variations in Earth’s climate.
“This new work gives credit to a mechanism that is much stronger than changes in solar irradiance alone,” Svensmark told The Australian.
“Solar irradiance has been the only solar forcing that has been included in climate models and such results show that the effect on climate is too small to be of importance,” he said.
“The new thing is that there exists an amplification mechanism that is operating on clouds in the atmosphere,” Svensmark said.
“Quantifying the impact of solar activity on climate from observations is found to be 5-7 times larger than from solar irradiance, and agrees with empirical variations in cosmic rays and clouds,” he said.
“This can therefore also explain why climate over the last 10,000 years correlates with solar activity, “Svensmark said.
“On time scales of millions of years there are much larger changes in the cosmic rays that has nothing to do with solar activity,” he said.
“So, this is an independent test of the mechanism and even here beautiful correlations are found,” he said.
But the Nature Communications paper says “the theory of ion-induced condensation should be incorporated into global aerosol models, to fully test the atmospheric implications.”
Professor Svensmark said since solar activity increased in the 20th century, part of the observed warming is caused by the sun.
“The logical consequence is that the climate sensitivity of CO2 is smaller than what climate models suggest which is 2-4 deg C for each doubling of CO2, since both CO2 and solar activity has had an impact”, he said.