Has the Sun gone to sleep?
Scientists are saying that the Sun is in a phase of "solar lull" - meaning that it has fallen asleep - and it is baffling them.
History suggests that periods of unusual "solar lull" coincide with bitterly cold winters.
Rebecca Morelle reports for BBC Newsnight on the effect this inactivity could have on our current climate, and what the implications might be for global warming.
- From the section Science & Environment