Low solar activity is expected to cause the winter jet stream to bring bitterly cold Arctic air, writes  DICK AHLSTROM

GLOBAL CLIMATE is warming, with 2010 expected to go down as yet another record year. You can count on our winters being colder than usual, however, at least for the next few years.

“There is a difference between global climate and regional climate, and there is a very peculiar thing we are finding about the European climate,” says Prof Mike Lockwood of the University of Southampton and the Rutherford Appleton Laboratory. Colder winters are expected because at the moment solar activity is very low.

Solar activity, in this case, does not mean direct heat or light from the sun but the energy emitted from the solar surface by sunspots. “What we are finding is that Europe and western Asia are particularly prone to solar influences, especially in winter,” Lockwood says. “What we are seeing is much cooler winters if solar activity is low.”

Last winter was particularly cold here and on the Continent, and low-temperature records were set.

Lockwood, who is Southampton’s professor of space and climate physics in the school of mathematical and physical sciences, believes we will see more of the same this winter. Climate change naysayers argue that temperature changes come down to a weakening or strengthening sun, but in fact Eurasia’s colder winters will be triggered by the jet stream, Lockwood explains. It is a phenomenon known as “set stream blocking”.

Sometimes the normal winter flow of the high-altitude jet stream “gets kinked into a reverse S-shape”, says Lockwood. “What happens in a blocking event is the normal flow changes, the warm westerlies get disrupted and we get cold Arctic air from the north and east.”

This in turn changes the weather we see on the ground. “Although the jet stream is very high up it is known to direct weather patterns further down.”

The thing that gets the jet stream into a winter twist is none other than the sun, but only when it is not very active.

“There is no doubt that the frequency of those blocking events in winter is higher when solar activity is low,” says Lockwood. “What was a slight surprise is that the sun was changing the jet stream, but only when the jet stream has travelled across the Atlantic and begins hitting land over Europe.”

Lockwood believes that the phenomenon may have been responsible for the “Little Ice Age” in Europe, a time between about 1650 and 1700 when people skated on the frozen Thames. During that time astronomers noted that there were no sunspots for 50 years, and Europe became extra cold.

Scientists have directly monitored solar activity continuously throughout the space age, giving us more than 40 years of data and a chance to assess the links between activity and temperatures, says Lockwood. Activity can also be inferred by other methods, and when examined over time it shows that recent years have seen very high activity.

“We find the sun typically goes through 400-year to 500-year solar minimums and maximums. This was one of the 24 grand maximums in the past 9,000 years,” he says, putting the recent solar levels in the top 15 per cent.

All of this is expected to change. Activity has rolled back and is expected to decline still further. “We have returned to the lowest solar-activity conditions since the 1920s,” Lockwood says. “I would anticipate more cold winters in Europe. This is despite and on top of a gradually warming world.”

Why Iceland's ash hit Ireland

The ash from the Eyjafjallajökull volcano (left) was spread across countries from Ireland down to Italy thanks to the weather phenomenon that is to make Irish winters colder in the coming years. Currently, weak solar activity is causing the wintertime jet stream to twist back on itself, channelling air first east and then west in a wide loop.

Unfortunately, this flow also picked up the Eyjafjallajökull ash and deposited it across countries on Europe's Atlantic seaboard and as far inland as Germany in the north and Italy in the south, says Prof Mike Lockwood of the University of Southampton. Normal Atlantic southwesterly air flows would have driven the ash away from us, but not with the jet stream blocking event. "This is the reason we all got covered in ash," Lockwood said.

He expects more of these to form in the coming few winters, and one can only hope that Eyjafjallajökull stays quiescent when the cold winds blow.

Prof Mike Lockwood will be discussing these issues this evening at a free public lecture organised by the Royal Irish Academy and The Irish Times. It takes place at 7pm in the Emmet Theatre, Arts Block, Trinity College Dublin