Sun's Output to Fall ... Leading to a Mini Ice Age?

The Register notes:

What may be the science story of the century is breaking this evening, as heavyweight US solar physicists announce that the Sun appears to be headed into a lengthy spell of low activity, which could mean that the Earth – far from facing a global warming problem – is actually headed into a mini Ice Age.

***

The announcement made on 14 June (18:00 UK time) comes from scientists at the US National Solar Observatory (NSO) and US Air Force Research Laboratory. Three different analyses of the Sun's recent behaviour all indicate that a period of unusually low solar activity may be about to begin.

***

This could have major implications for the Earth's climate. According to a statement issued by the NSO, announcing the research:

An immediate question is whether this slowdown presages a second Maunder Minimum, a 70-year period with virtually no sunspots [which occurred] during 1645-1715.

As NASA notes:

Early records of sunspots indicate that the Sun went through a period of inactivity in the late 17th century. Very few sunspots were seen on the Sun from about 1645 to 1715. Although the observations were not as extensive as in later years, the Sun was in fact well observed during this time and this lack of sunspots is well documented. This period of solar inactivity also corresponds to a climatic period called the "Little Ice Age" when rivers that are normally ice-free froze and snow fields remained year-round at lower altitudes. There is evidence that the Sun has had similar periods of inactivity in the more distant past.

During the Maunder Minimum and for periods either side of it, many European rivers which are ice-free today – including the Thames – routinely froze over, allowing ice skating and even for armies to march across them in some cases.

"This is highly unusual and unexpected," says Dr Frank Hill of the NSO. "But the fact that three completely different views of the Sun point in the same direction is a powerful indicator that the sunspot cycle may be going into hibernation."

***

According to the NSO:

Penn and Livingston observed that the average field strength declined about 50 gauss per year during Cycle 23 and now in Cycle 24. They also observed that spot temperatures have risen exactly as expected for such changes in the magnetic field. If the trend continues, the field strength will drop below the 1,500 gauss threshold and spots will largely disappear as the magnetic field is no longer strong enough to overcome convective forces on the solar surface.

In parallel with this comes research from the US Air Force's studies of the solar corona.

***

"Cycle 24 started out late and slow and may not be strong enough to create a rush to the poles, indicating we'll see a very weak solar maximum in 2013, if at all. If the rush to the poles fails to complete, this creates a tremendous dilemma for the theorists ... No one knows what the Sun will do in that case."

According to the collective wisdom of the NSO, another Maunder Minimum may very well be on the cards.

"If we are right," summarises Hill, "this could be the last solar maximum we'll see for a few decades. That would affect everything from space exploration to Earth's climate."

***

The big consequences of a major solar calm spell, however, would be climatic. The next few generations of humanity might not find themselves trying to cope with global warming but rather with a significant cooling. This could overturn decades of received wisdom on such things as CO₂ emissions, and lead to radical shifts in government policy worldwide.

The Telegraph confirms:

Sunspot activity, which follows an 11-year cycle, is due to peak in 2013 after which it will start to wane slightly.

But astronomers think the next upswing will be less intensive than normal, or could fail to happen at all.

That could affect weather on Earth because low solar activity has been linked to low global temperatures in the past.

Between 1645 and 1715 almost no sunspots were observed, a solar period which came to be called the Maunder Minimum.

During those decades Europe suffered frequent unusually harsh winters, and the time was later termed the Little Ice Age.

***

Three studies, presented at a meeting of the American Astronomical Society's solar physics division, all point towards declining sunspot activity into the next decade.

Frank Hill, of the National Solar Observatory in New Mexico, who worked on one of the studies, said: "The fact that there are three separate lines of evidence all pointing in the same direction is very compelling."

But Joanna Haigh professor of atmospheric physics at Imperial College London, said global warming could override any cooling effect on the Earth's climate.

However, she cautioned: "Even if the predictions are correct, the effect of global warming will outstrip the sun’s ability to cool even in the coldest scenario.

"And in any case, the cooling effect is only ever temporary. When the sun’s activity returns to normal, the greenhouse gases won't have gone away."

And Agence France-Presse reports:

For years, scientists have been predicting the Sun would by around 2012 move into solar maximum, a period of intense flares and sunspot activity, but lately a curious calm has suggested quite the opposite.

According to three studies released in the United States on Tuesday, experts believe the familiar sunspot cycle may be shutting down and heading toward a pattern of inactivity unseen since the 17th century.

The signs include a missing jet stream, fading spots, and slower activity near the poles, said experts from the National Solar Observatory and Air Force Research Laboratory.

"This is highly unusual and unexpected," said Frank Hill, associate director of the NSO's Solar Synoptic Network, as the findings of the three studies were presented at the annual meeting of the American Astronomical Society's Solar Physics Division in Las Cruces, New Mexico.

"But the fact that three completely different views of the Sun point in the same direction is a powerful indicator that the sunspot cycle may be going into hibernation."

Solar activity tends to rise and fall every 11 years or so. The solar maximum and solar minimum each mark about half the interval of the magnetic pole reversal on the Sun, which happens every 22 years.

Hill said the current cycle, number 24, "may be the last normal one for some time and the next one, cycle 25, may not happen for some time.

"This is important because the solar cycle causes space weather which affects modern technology and may contribute to climate change," he told reporters.

Experts are now probing whether this period of inactivity could be a second Maunder Minimum, which was a 70-year period when hardly any sunspots were observed between 1645-1715, a period known as the "Little Ice Age."

"If we are right, this could be the last solar maximum we'll see for a few decades. That would affect everything from space exploration to Earth's climate," said Hill.

This trend could explain why we haven't experienced any warming recently. As AFP notes:

"Recent solar 11-year cycles are associated empirically with changes in global surface temperature of 0.1 Celsius," said Judith Lean, a solar physicist with the US Naval Research Laboratory.

If the cycle were to stop or slow down, the small fluctuation in temperature would do the same, eliminating the slightly cooler effect of a solar minimum compared to the warmer solar maximum. The phenomenon was witnessed during the descending phase of the last solar cycle.

This "cancelled part of the greenhouse gas warming of the period 2000-2008, causing the net global surface temperature to remain approximately flat -- and leading to the big debate of why the Earth hadn't (been) warming in the past decade," Lean, who was not involved in the three studies presented, said in an email to AFP.

A study in the March 2010 issue of Geophysical Research Letters explored what effect an extended solar minimum might have, and found no more than a 0.3 Celsius dip by 2100 compared to normal solar fluctuations.

"A new Maunder-type solar activity minimum cannot offset the global warming caused by human greenhouse gas emissions," wrote authors Georg Feulner and Stefan Rahmstorf, noting that forecasts by the Intergovernmental Panel on Climate Change have found a range of 3.7 Celsius to 4.5 Celsius rise by this century's end compared to the latter half of the 20th century.

"Moreover, any offset of global warming due to a grand minimum of solar activity would be merely a temporary effect, since the distinct solar minima during the last millennium typically lasted for only several decades or a century at most."