BBC NEWS -- Sunspots reaching 1,000-year high

A new analysis shows that the Sun is more active now than it has been at anytime in the previous 1,000 years.
Scientists based at the Institute for Astronomy in Zurich used ice cores from Greenland to construct a picture of our star's activity in the past.

They say that over the last century the number of sunspots rose at the same time that the Earth's climate became steadily warmer.

This trend is being amplified by gases from fossil fuel burning, they argue.

In particular, it has been noted that between about 1645 and 1715, few sunspots were seen on the Sun's surface.

This period is called the Maunder Minimum after the English astronomer who studied it.

It coincided with a spell of prolonged cold weather often referred to as the "Little Ice Age". Solar scientists strongly suspect there is a link between the two events - but the exact mechanism remains elusive.

Over the past few thousand years there is evidence of earlier Maunder-like coolings in the Earth's climate - indicated by tree-ring measurements that show slow growth due to prolonged cold.

Over the past few hundred years, there has been a steady increase in the numbers of sunspots, a trend that has accelerated in the past century, just at the time when the Earth has been getting warmer.

The data suggests that changing solar activity is influencing in some way the global climate causing the world to get warmer.

Over the past 20 years, however, the number of sunspots has remained roughly constant, yet the average temperature of the Earth has continued to increase.

This is put down to a human-produced greenhouse effect caused by the combustion of fossil fuels.