Oliver "MainlyMartian" Morton is ticked.

There's a nice new paper in Nature by some NASA Ames and USGS people (including Bob Haberle, who used to have a sign saying "Commander of the Solar System" taped to his office door) on the link between climate and albedo on Mars. As my colleague Katharine Sanderson reports, they found that warming of darker patches creates winds that move the lighter dust around so that the darker patches grow and get warmer still -- a nice positive feedback that is presumably reset by global dust storms and the like.

This provoked me to a little venting on the Nature website about the absurd climate skeptic riff that there's warming going on all over the solar system and that since the thing all the warming places have in common is the sun that must be the cause.

Well, there does seem to be evidence that it is at least part of the cause.

Over the past few thousand years there is evidence of earlier Maunder-like coolings in the Earth's climate - indicated by tree-ring measurements that show slow growth due to prolonged cold.

In an attempt to determine what happened to sunspots during these other cold periods, Dr Sami Solanki and colleagues have looked at concentrations of a form, or isotope, of beryllium in ice cores from Greenland.

The isotope is created by cosmic rays - high-energy particles from the depths of the galaxy.

The flux of cosmic rays reaching the Earth's surface is modulated by the strength of the solar wind, the charged particles that stream away from the Sun's surface.

And since the strength of the solar wind varies over the sunspot cycle, the amount of beryllium in the ice at a time in the past can therefore be used to infer the state of the Sun and, roughly, the number of sunspots. . .

He says that the reconstruction shows the Maunder Minimum and the other minima that are known in the past thousand years.

But the most striking feature, he says, is that looking at the past 1,150 years the Sun has never been as active as it has been during the past 60 years.

Over the past few hundred years, there has been a steady increase in the numbers of sunspots, a trend that has accelerated in the past century, just at the time when the Earth has been getting warmer.

The data suggests that changing solar activity is influencing in some way the global climate causing the world to get warmer.

Over the past 20 years, however, the number of sunspots has remained roughly constant, yet the average temperature of the Earth has continued to increase.

This is put down to a human-produced greenhouse effect caused by the combustion of fossil fuels.

This latest analysis shows that the Sun has had a considerable indirect influence on the global climate in the past, causing the Earth to warm or chill, and that mankind is amplifying the Sun's latest attempt to warm the Earth.

My opinions have no value, but they are appropriately priced. I find arguments for multiple causes for our observed warming to be far more likely than any single cause argument. That GHGs and solar variability might be amplifying individual effects seems likely to me, and I suspect that albedo effects such as those Oliver notes on Mars are also true on earth. And other things as well.

What isn't at all clear to me is the relative magnitudes of these effects or what future changes might bring. If the sun has never been more active than in the last 60 years, capping a trend hundreds of years old, and seems to have held steady for the past 20 years, then what about the near future? I've read elsewhere that some researchers have predicted a decline in activity for the next 100 years.

As I understand it, variations in magnetic fields also matter since they act as cosmic ray shields. The sun's magnetic field, the earth's magnetic field and the solar wind all affect cosmic rays. It may be that the net effects of these factors are small compared to GHG concentrations, but I haven't seen a comprehensive treatment. Usually GHG advocates seize on data about insolation, which has not risen markedly, but don't mention the cosmic ray angle.

Is there some analysis of all these issues available in a form that a simple grass farmer could choke down? Am I so open minded that my brains have fallen out?