Last night in the UK, the BBC broadcast this fascinating documentary regarding the Sun (YouTube video appended below).It was presented by two of my favourite TV personalities, Dr Helen Czerski and Kate Humble. It starts by pointing out that the Sun is currently at solar maximum – the point of maximum activity in a cycle that typically occurs every 11 years. It ends by presenting data (obtained from 17 years of continuous observation) indicating that the Sun is also now approaching a grand solar minimum – something it last did over 300 years ago. In between, it describes all sorts of things about how the Sun works; and includes dramatic footage of Kate Humble witnessing a total solar eclipse in Australia and the Aurora Borealis in Sweden. I thought I understood most of this stuff and so, apart from the awesome cinematography of the above events, it was tempting to think I might have heard it all before – solar wind… blah blah blah… solar storms… blah blah blah… coronal mass ejections, electromagnetic pulses, widespread power blackouts… However, no-one should under-estimate the real problems that a coronal mass ejection (CME) could cause. We can do this by extrapolating from (1) the effects of routine solar wind and (2) from the occasions when the Earth has been affected my CMEs in the past, such as in Quebec in 1989 and Malmo in 2003. In both cases, however, the Earth was only affected by a small part of the CME. If it was to be struck by the full force of a CME, the problems could be much more serious and much more widespread. Indeed, Lloyds of London has compiled a detailed assessment of all the things that could be affected, such as: communications, food, finance, fuel, health services, sanitation, transport and water supply. [See page 15 in Space Weather: Its impacts on Earth and the implications for business (PDF)]. Nevertheless, I want to focus on the last 10 minutes of the programme, where the results of observations from the (National Optical Astronomy Observatory’s) McMath-Pierce Solar Telescope in Arizona are presented. This has been used to look at the average strength of the magnetic field within individual sunspots for the last 17 years. As such, it has observed more than an entire solar cycle; with the number of visible sunspots ranging from less than 5 (at solar minimum) to as many as 100 (at solar maximum). The remarkable thing is that, instead of rising and falling during the solar cycle, the average magnetic strength of the sunspots has been steadily decreasing over the last 17 years. This would appear to confirm the argument made by Fred Singer and Dennis Avery, in their book Unstoppable Global Warming, that the Sun also has longer-term cycles in sunspot activity. In other words, this declining trend in magnetic field strength suggests that the Sun is now heading towards another ‘grand solar minimum’; similar to that primarily responsible for a period of colder than normal weather in the 17th Century (i.e. known as the Little Ice Age), during which the River Thames regularly froze (something it has only done once in the last 200 years – in 1963). However, before all those climate change sceptics out there in the deniosphere get all excited, this is not good news! Just as with the cooling effects of particulates and aerosols in our atmosphere, the effects of another approaching grand solar minimum will only be temporary. The very best thing we can say is that, were it to materialise, another Little Ice Age would give us a little more time to phase out fossil fuels and make carbon capture and storage work. However, the one thing it will not alter is this: The burning of fossil fuels is the primary cause of 20th Century warming, which is an underlying trend that is likely to overwhelm all other (cooling) effects unless we stop the super-exponential growth of CO2 emissions of the last 200 years (i.e. following a ‘J-curve’ – with an annual percentage growth progressively increasing over time). http://www.youtube.com/watch?v=l6T5TQa8MlE Addendum (25th June 2013): Since writing this yesterday, as stated in response to RobertScribbler below, it has occurred to me that the difference between day and night temperatures is not as great as it would be if we had no atmosphere, which suggests that what the atmosphere does is more important than what the Sun does: Let us assume that total solar irradiance could reduce by 1.5% over a 200 year period. In the 200 yr period up to that (approaching) grand solar minimum, it is likely that the average water content of our atmosphere will have increased by at least three times as much (i.e. 4.5%) and CO2 by ten times that (i.e. at least 45%). Am I right, or am I right?