Solar clues on climate change

In their study of ice cores, an Al Ain academic and foreign researchers have confirmed the occurrence of major solar storms in the 8th and 10th centuries, helping to advance our understanding of global weather patterns.

Prof Ala Aldahan of UAE University co-authored a paper about research that identified radioactive beryllium-10, associated with solar storms, in ice cores from Greenland and the Antarctic. Joe Raedle / Getty ImagesShow less

No one needs to be told that the Sun is vital to life on earth.

This extraordinary star, which is about 4.6 billion years old, fuses hundreds of millions of tonnes of hydrogen into helium every second, and in doing so generates colossal amounts of energy that keeps our planet, 93 million miles away, pulsing with activity.

It may seem, looking up in daytime, that the Sun’s activity is constant and unvarying.

Yet a researcher in Al Ain has helped to shed fascinating light on some of the changes in solar activity during centuries past.

Professor Ala Aldahan, from UAE University, is part of a team who have used ice cores from Greenland and the Antarctic to better understand what are known as solar proton events, or solar storms. These involve the Sun sending out protons – the positively charged particles found in the nuclei of atoms – with such high energy that they are able to enter the Earth’s magnetic field.

The largest properly recorded solar proton event took place in 1859. At the time of this geomagnetic storm, dark patches known as sunspots were seen in the sun, while aurorae − beautiful lights in the night sky − were visible to people in the northern and southern hemispheres. Even sky watchers a long way from the poles, the areas from which aurorae are more commonly seen, could view them. In more recent times, there have been other large solar proton storms, such as a large one in 1989 that knocked out power supplies in parts of Canada.

In fact, as today’s sophisticated recording equipment demonstrates, solar storms happen quite often, although typically they are modest in scale. The United States’ National Oceanic and Atmospheric Administration lists 27 as having taken place from January 2012 until now, but the numbers fluctuate from year to year, with none at all recorded between 2007 and 2009.

Thanks to a Japanese study in 2012, scientists have for the past few years suspected that solar proton events of a very large magnitude took place in the 8th and 10th centuries.

This research found higher levels of radioactive carbon in tree rings from 774/75 and 993/4, indicating that something unusual happened at both of these times.

A new paper co-authored by Prof Aldahan, published in the journal Nature Communications and entitled Multiradionuclide evidence for the solar origin of the cosmic-ray events of AD 774/5 and 993/4, provides confirmation that these events were, indeed, solar storms.

As the authors note, other suggestions for what may have caused the radioactive carbon spike have included a comet or a gamma-ray burst, the latter being flashes of gamma rays, a type of electromagnetic radiation caused by explosions in other galaxies.

The latest research identified in ice cores a radioactive form of the element beryllium at a time that corresponds to when the storms were thought to have taken place.

Radioactive beryllium-10 (10Be), a radionuclide (or radioactive nuclide) is a form of beryllium with six neutrons and four protons in its nucleus. It is associated with solar proton storms, since it is created when atmospheric particles are struck by the protons sent out by the Sun. Its presence therefore strongly suggests that a solar proton storm was responsible for the abnormal carbon readings.

Further evidence in support of this comes from data from one of the Greenland ice cores related to an isotope of chlorine, known as chlorine-36 (36Cl), which has 19 neutrons and 17 protons.

The events that took place in the 8th and 10th centuries were much more severe than the solar storm in 1859, when communications systems were badly affected. And, according to the scientists, the 774/5 event was at least five times stronger than any solar proton event between 1956, when a particularly severe solar storm was recorded, and 2005.

“Fortunately, at that time [in the eighth and 10th centuries] there were no electrical power supplies, ground and satellite communication systems, which will be knocked out immediately,” said Prof Aldahan.

Were an event of the magnitude of these earlier ones to happen now, the consequences, in terms of disruption to communications and power supplies, would be very severe. It would also affect spacecraft and their crews.

“Work like the one presented can help scientists understand sudden variabilities that may occur in the climate system,” said Prof Aldahan, who was previously based at the Department of Earth Sciences at Uppsala University in Sweden.

The ice cores used in his study were provided by the Centre for Ice and Climate at the University of Copenhagen, where there is a large refrigerated storage centre.

Prof Aldahan helped to identify the most suitable ice cores, prepared samples for the extraction of the 10Be and 36Cl and interpreted the results of the sample analysis by mass spectrometry, a method that involves separating out particles based on their mass-to-charge ratio.

The paper’s senior author was Florian Mekhaldi, a PhD student at Lund University in Sweden.

“This is the first time that such strong solar events have been discovered from cosmogenic isotopes in ice cores and tree rings,” said Mr Mekhaldi.

“We will, in the future, try to find more of these peaks so that we can better understand their nature and how frequent they are.”

Indeed there are likely to be many more interesting results in the years to come, offering a better understanding of solar storms. Prof Aldahan is among those involved in these efforts, which involve further analysis of Greenland ice cores.

“The further work is being carried out to identify other periods of large solar storms in the Earth’s palaeoclimatic record, both in the near past [the past 1,000 years] and in the distant past [many thousands of years],” he said.

“The aim is to link these events to global climate change patterns and to advance further understanding of feedback in the system.”