Scientists have barely scratched the surface of the task of recognising and modelling natural cycles of climate change.
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 super-grand cycles, going back 120,000 years. Their research has established that the current super-grand 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 so-called 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.
- This paper has now been retracted https://retractionwatch.com/2020/03/04/heavily-criticized-paper-blaming-the-sun-for-global-warming-is-retracted/