WRITING ABOUT the Sun at the end of August this year might seem ironic, even sadistic. As a reminder, especially for readers in the East and South East of England, the Sun is the big round yellow thing in the sky that made a robust appearance in July, but that has largely absconded since.

The Sun will, however, be enjoying some company soon. Next month, Nasa will launch the Solar Terrestrial Relations Observatory (Stereo). This consists of two probes, one just ahead of the Earth’s orbit and the other behind it, which will examine coronal mass ejections, or solar flares.

Coronal mass ejections really are, well, massive. The Sun can throw out eruptions consisting of ten billion tons of its atmosphere, measuring six million miles across, or well over five times its own width, at a speed of approximately a million miles an hour. That is one hell of a celestial fireball.

This is all very fascinating, you might respond (a little bemused that there seem to be two Science Notebooks on these pages today), but should Stereo interest me? An awful lot as it happens. For if this £250 million, two-year project produces the evidence that some scientists hope and believe it will, it could transform the raging debate about global warming.

There has long been a minority school of thought that is deeply sceptical about the extent to which rising temperatures on this planet can be explained, and blamed, on human activity. The most persuasive subsection of this community is convinced that the principal cause of climate change on Earth is the intensity of solar activity.

This argument is virtually unknown to the wider public. In part this is because the data required truly to prove the case have not been available, although Stereo should change that. It is also because the control exercised in this area by those who contend that global warming can only be man-made resembles that which the Roman Catholic Church once held over the character of the solar system. Public discussion is dominated by those inclined to the most doom-laden predictions, and this lobby is not that wild on the notion that astronomy may come up with a compelling alternative hypothesis. And it probably has not helped the proponents of solar influence that one of their most prominent advocates rejoiced in the name Harry van Loon.

There are, nonetheless, three sound reasons to be open to this explanation.

The first is that the conventional global warming stance has huge limitations. It is widely accepted that the average surface temperature on Earth has risen by about 0.5 degrees centigrade over the past 125 years or so. Yet if man’s activities were driving this warming process then one would expect the rate of that increase to have accelerated in modern times in response to increasing industrialisation, aircraft flights and so on. This evidence has singularly failed to materialise, despite satellites having been available to measure the Earth’s temperature since the late 1970s.

This conundrum is compounded by the knowledge that dramatic climate change on Earth has occurred in the relatively recent past, but well before contemporary inventions came into play. Examinations of ancient tree rings and other data show that temperatures cooled in the 11th century, but rose quite sharply in the 150 years after that, when the Vikings were able to settle in Greenland. Then temperatures slumped again, so much so that the period 1645-1715, when the Thames froze solid most winters in London, is now referred to as “the little ice age”, only to reverse course after 1800. None of this could possibly have been triggered by the deeds of low-cost airlines.

Finally, there is what we can already ascertain about the Sun itself. Solar activity has short-term fluctuations such as the familiar sunspot cycle with a duration of about 11 years, and much longer term patterns of solar flares about which we understand less.

There is little doubt that daily atypical solar activity can have an impact on our climate. That is hardly surprising as total solar irradiance (TSI) can vary as much in a space of time as short as a week as the total energy used by humans beings, globally, for a year. The overall energy output of the Sun is far greater in a single second than all human activity could produce in a million years. To the layman such as myself, the claim that the big round yellow thing in the sky may have more influence on the condition of this planet than the 10.45 easyJet flight from Stansted to Palma does have a kind of logic. We laymen are not alone.

In 2003 a team from Columbia University reported that the Sun’s heat had increased by 0.05 per cent a decade since the 1970s, the point when completely reliable data started to be collected. This would be enough to have a big influence on the Earth’s climate if it were a trend that had continued for many decades. The Columbia team believed that the pattern could be traced back to the mid-19th century at the very least. Others, working with carbon data material, insist that the Sun has been more vigorous in the past six decades than at any time in 8,000 years. It defies reason, surely, to conclude that this would be irrelevant to the climate. Indeed, there is a deep arrogance implicit in the sentiment that if anything on Earth is changing, human beings must be responsible.

A decade ago, H. N. Priem, the Dutch geologist, predicted: “The current and anticipated fleet of spacecraft devoted to the study of solar and solar-terrestrial physics will probably prove to have more bearing on the understanding and forecasting of climate change than the orchestrated assessments by politically motivated international panels biased towards global warming exclusively by the enhanced greenhouse effect.”

Stereo should shed illuminating light, in more ways than one, on this matter. It will provide real fuel for this discussion. Not that, alas, this will do much for our Bank Holiday weekend .

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