Does the BBC have a shred of credibility left in its coverage of global warming? The question is prompted by last night's puerile report by their environment correspondent David Shukman on the warning that emerged from the Copenhagen climate summit that sea levels could rise by a metre by the century's end.

This is a deadly serious topic. Such a rise in sea levels would have a catastrophic impact on the lives of millions.

So why did the BBC's coverage treat its viewers like morons? Shukman took himself with a tape measure to the top of a sea wall and showed what an extra metre of water would mean, measuring from the top of the wall.

And very dramatic it was. The briny would be lapping round his chin. Alarming stuff. Except that the top of a sea wall is not sea level. Most sea walls rise 10 or 15 feet above high water mark to cope with tide surges and storms. That's what sea walls are for.

But of course if Shukman had got out his tape and measured a metre above high water mark, it would have been far less dramatic. So the BBC decided to play fast and loose with the facts just to make a cheap point.

Global warming is too important an issue to be covered by such gimcrack reporting. Last night's report simply reinforces the view that the BBC has bought hook, line and sinker the most apocalyptic assessment of the impact of global warming and is not going to allow a more informed and grown-up debate to take place. Is that what we want from a public service broadcaster?