Scientists find evidence cosmic rays influence Earth’s climate

High-energy radiation from space, known as galactic cosmic rays, can affect Earth’s climate by increasing cloud cover and causing an “umbrella effect”, according to scientists.

Besides atmospheric temperature and the amount of water vapour in the air, cosmic rays beaming down through space also contribute towards cloud formation. This is particular during Earth’s geomagnetic reversal — a phenomenon where the planet's overall magnetic field flips.

The rays can enhance the formation of low-lying clouds or increase the global cloud cover ultimately leading to the cooling of Earth's atmosphere.

Previous studies using data from the meteorological observation not prove the theory as the data showed only minute changes in the amounts of galactic cosmic rays and cloud cover.

Thus, for the new study, researchers from the Kobe University in Japan, analysed Earth’s last geomagnetic reversal transition 780,000 years ago.

During the period, the Earth’s magnetic strength fell to less than one-fourth and galactic cosmic rays increased by over 50 per cent. This spiked the global cloud cover and enabled detection of the impact of cosmic rays on climate at a higher sensitivity, according to the study published in the Scientific Reports journal.

Combined effect of rays and cloud cover, led to a high atmospheric pressure in Siberia. The effect caused the East Asian winter monsoon to become stronger, the researchers said.

Focusing on the phenomenon, the researchers also investigated changes in particle size and accumulation speed of loess layer dust — sediment created by the accumulation of wind-blown silt — in two locations of China’s Loess Plateau.

Dust transported for 2.6 million years has formed such layers, that can reach up to 200 metres in thickness, in the plateau, located just south of the Gobi Desert near the border of Mongolia.

During the last geomagnetic reversal, the researchers found evidence of stronger winter monsoons: The particles became coarser and silt was accumulated up to three times faster in both locations.

This suggests that the increase in cosmic rays was accompanied by an increase in low-cloud cover, the umbrella effect of the clouds cooled the continent and Siberian high atmospheric pressure became stronger.

The researchers also found evidence from an annual average temperature drop of 2-3 degrees Celsius and increase in annual temperature ranges from the sediment in Osaka Bay in Japan.

With the increase in climate change events, understanding the galactic cosmic rays’ role in the global warming may be important, the researchers said.

“The Intergovernmental Panel on Climate Change has discussed the impact of cloud cover on climate in their evaluations, but this phenomenon has never been considered in climate predictions due to the insufficient physical understanding of it”, Hyodo said.

“This study provides an opportunity to rethink the impact of clouds on climate. When galactic cosmic rays increase, so do low clouds, and when cosmic rays decrease clouds do as well, so climate warming may be caused by an opposite-umbrella effect,” said Masayuki Hyodo Professor at the University’s Research Center for Inland Seas.

“The umbrella effect caused by galactic cosmic rays is important when thinking about current global warming as well as the warm period of the medieval era,” Hyodo added.

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