David Whitehouse: Sun's hotspots may have role in global warming

From a talk given by the BBC Science Correspondent at the Royal Institution in London

Our Sun's story is one that is repeated across the length and breadth of the cosmos, but it is no less remarkable for that. There are about a hundred billion galaxies out there with each having, on average, about a hundred billion stars, and many of them are like the yellow star that gives us warmth and light. There are brighter stars, there are more numerous fainter stars, but in terms of mass and brilliance our Sun is average.

Average is good. Our star is long-lived and stable. It has been shining for about four and a half billion years at roughly the same intensity (it was slightly brighter in the past). It also has a family of planets, something that we now believe is commonplace. That means our Sun has provided a secure long-term environment for life to develop on Earth, providing it with enough energy to thrive but not too much to threaten it.

But there may come a time when our Sun ceases to be our friend. There is evidence that just a few centuries ago something happened to the Sun. During the 17th century - roughly coincident with the reign of Louis XIV, the "Sun King" - the Sun ran out of sunspots. At the same time the Earth chilled, entering what is termed the Little Ice Age.

Today all the talk is of global warming and man's burning of greenhouse gases that are causing it. But think on this. There is evidence that even today our Sun's behaviour is unusual - that it is going through a high of sunspot activity unprecedented in the past 8,000 years, that is since the end of the last Ice Age. It could be that the Sun is having an influence on the warming we may be observing. If we ignore this and focus only on greenhouse gasses we may be missing the moving force behind climate change. We cannot ignore the Sun.