In February 2007, depending on what newspaper you read, you might have seen an article detailing a "controversial new theory" of global warming.

The idea was that variations in cosmic rays penetrating the Earth's atmosphere would change the amount of cloud cover, in turn changing our planet's reflectivity, and so the temperature at its surface.

This, it was said, could be the reason why temperatures have been seen to be varying so much over the Earth's history, and why they are rising now.

observations suggest that the Sun's output may have started to wane from its "grand maximum".

But if the Sun wanes and temperatures on our planet continue to rise, as the vast majority of scientists in the field believe, the solar-cosmic ray concept of global warming can be laid to eternal rest.

And if humankind has done nothing to stem the rise in greenhouse gas emissions by then, it will be even harder to begin the task.