Climate change: the role of ash, and volcanoes

The excessive zeal of some scientists has made it difficult to discuss climate change (which, amusingly, was first headlined simply as global cooling, then global warming). But it's universally agreed (I think) that the Earth has been a lot hotter, and a lot colder, in past millenia. The question is, what's happening now?

Up in Greenland, they're now growing strawberries and potatoes; and last month the albedo of the ice sheet was lower than in any April in the last dozen years, hinting at an even bigger melt than before.

Yet there is still debate over whether Earth's total ice cover is growing or decreasing, as a Dutch study reported last month. It seems that while the Arctic's is melting, the Antarctic is piling on more.

The network of causes and effects is complex: CO2 and high-altitude water vapour (quite a lot from planes, I think) interrelate with air and sea temperature (which vary around the globe). An explanation as to why ice is melting in one place and melting in another is that particulates from burning forests and fossil fuels are settling on Northern glaciers, absorbing energy from sunlight and conducting extra heat into the ice below.

The ash can also come from volcanic eruptions - but the causal connection goes both ways. Another study, published last December by researchers in Germany and the USA, seems to show that as ice cover decreases and sea levels rise over long periods, tectonic plates are warped by the changes in their burden and volcanic activity increases.

And the causes can sometimes oppose each other. I recall how in 2010, when flights over the UK were banned because of the ash cloud from Iceland's Eyjafjallajökull volcano, we saw not grey, cloudy days but brilliant sunshine and chilly, starry nights. I wonder what is the relative importance of hydrocarbon emissions and water vapour?

Enough brickbats have been thrown at those who forgot their professional scientific objectivity in the debate. It's time for both sides to reexamine evidence and hypotheses with open minds.

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