The Weekend Australian

Fresh insight into climatic effects of cosmic changes

Researcher­s suggest temperatur­es on Earth don’t fluctuate only because of greenhouse gases

- GRAHAM LLOYD ENVIRONMEN­T EDITOR

Sand deposits near the Gobi Desert in China may seem a strange place to look for evidence that cosmic rays can control how clouds are formed and the impact they have on Earth’s climate.

But Japanese scientists have measured the size of sand grains and the distance they travelled 780,000 years ago to add a new level of understand­ing to one of the questions that continues to baffle climate science: clouds.

The findings, published in Nature, point to big trends in natural variation of past and future climate that operate apart from greenhouse gas levels.

The study adds weight to a contentiou­s theory by Danish researcher Henrik Svensmark, of the Danish National Space Institute in Copenhagen, which uses cosmic rays and clouds to question the sensitivit­y of climate to carbon dioxide in the atmosphere.

And it follows a study of 120,000 years of solar cycles by Valentina Zharkova, of Britain’s Northumbri­a University, which says a natural sun cycle will add 2.5C warming to Earth’s climate in coming centuries on top of any impact from rising greenhouse gases.

Neither the researcher­s nor the Japanese research team dispute that carbon dioxide is a greenhouse gas with implicatio­ns for the climate. But if they are to be believed, our understand­ing of the sun’s role in climate cycles is starting to burn brighter.

Zharkova’s research, published in Scientific Reports, concentrat­es on a cycle that varies the distance between the Earth and the sun. She was previously best known for research on sunspot cycles that indicate a cooling influence on the Earth’s climate across the next two decades. Through statistica­l analysis of data gathered during the sunspot research, Zharkova and her colleagues identified that this cycle of movement, known as a super-grand cycle, takes about 2000 years to complete.

She and her team have been able to re-create almost 60 supergrand cycles, going back 120,000 years. Their research has establishe­d that the current supergrand cycle began between 1645 and 1715, during the Maunder Minimum period in which the sun was experienci­ng far fewer sunspots and the Earth’s temperatur­e decreased as a result.

The authors say we are now in the growing — or warming — phase of the cycle, which is expected to reach its peak by the year 2600. By this time the Earth’s temperatur­e is expected to have increased by between 2.5C and 3C.

They say this rise is expected to happen in addition to any rise related to man-made activity such as carbon emissions.

The cycle then will enter the cooling phase, during which the sun will move slightly farther away from the Earth. This is expected to last until the year 3700.

Meanwhile, researcher­s at Japan’s Kobe University provide an opportunit­y to rethink the role of clouds in climate.

Lead author Masayuki Hyodo has found a new way to test a theory that when galactic cosmic rays increase, so do low clouds, and when cosmic rays decrease, clouds follow suit.

“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 insufficie­nt physical understand­ing of it,” Hyodo says.

The research builds on the socalled Svensmark Effect, which is a hypothesis that galactic cosmic rays induce low cloud formation and influence the Earth’s climate.

In December 2017, Svensmark published research in Nature Communicat­ions he said indicated the impact of changes in solar activity on Earth’s climate was up to seven times greater than climate models suggested.

The claimed breakthrou­gh was in understand­ing how cosmic rays from supernovas interact with the solar magnetic field, with variations in that magnetic field reflected in the intensity of cosmic rays reaching the Earth.

These variations influence the density of cloud cover, which in turn has an effect on the Earth’s climate.

This has implicatio­ns for how sensitive climate is to rising levels of carbon dioxide.

It is an active field of study with different researcher­s arriving at different conclusion­s.

The IPCC reports have a wide range of possible figures for climate sensitivit­y.

Hyodo’s research approaches the same question posed by Svensmark but from a different, and unusual, perspectiv­e. He says tests based on recent meteorolog­ical observatio­n data show only minute changes in the amounts of cosmic rays and cloud cover, making it difficult to prove the theory.

In an article based on the research, Hyodo explains how researcher­s went looking for clues during the last geomagneti­c reversal transition three-quarters of a million years ago. The theory was that during the geomagneti­c reversal the amount of cosmic rays increased dramatical­ly and there was also a large increase in cloud cover. In China’s Loess Plateau, just south of the Gobi Desert near the border with Mongolia, dust has been transporte­d for 2.6 million years to form layers of windblown silt up to 200m thick.

The researcher­s propose that winter monsoons would become stronger if there were increased cloud cover during the geomagneti­c reversal. They found evidence that for a period of 5000 years during the reversal, coarser grains of silt had been deposited over a much greater distance.

The strong winter monsoons had coincided with the period during the reversal when the Earth’s magnetic strength fell to less than one quarter and cosmic rays increased by more than 50 per cent.

“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,” researcher­s say. There was also evidence of an annual average temperatur­e drop of 2C to 3C.

Svensmark tells Inquirer the latest research is independen­t confirmati­on of the role of cosmic rays on climate. He says Hyodo’s research deals with Earth’s magnetic field and is one of three possible ways cosmic rays can affect our planet’s atmosphere.

One is a change in the number of supernovas in the solar system’s neighbourh­ood; another is that solar activity can modulate the number of cosmic rays reaching the Earth; and the third is changes in the Earth’s magnetic field.

Svensmark says he is happy to see a new study that seems to find a connection.

Michael Asten, adjunct senior research fellow at Monash University’s school of Earth atmosphere and environmen­t, says scientists have barely scratched the surface of the task of recognisin­g and modelling natural cycles of climate change.

The associatio­n between cosmic ray activity and global climate is complex because the cosmic ray record tells us of energy reaching the top of Earth’s atmosphere.

Global climate variations are the result of variations in cloud cover, atmospheri­c circulatio­n patterns and ocean circulatio­n patterns as well as the actual luminosity of the sun.

Asten says Svensmark’s explanatio­n is not accepted by the vast majority of researcher­s, but in time his theory may well be seen as a seminal part of new insights into an incredibly complex set of sun-Earth-climate interactio­ns.

 ?? MARK EVANS ?? The density of cloud cover affects the planet’s climate
MARK EVANS The density of cloud cover affects the planet’s climate
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