More on whether the weather is climate

Here's a letter I sent to the editor of The Economist:

Sir,

Last winter, we were told by scientists that it was `stupid' to take the cold weather as evidence against global warming. Yet this winter you are quite happy to speculate, entirely against the consensus view, that the cold weather is evidence for global warming (`A Cold Warming', Dec 4^th). In support of this fancy, you cite `some' evidence that summer heat `may' induce shifts in atmospheric circulation that `might' encourage seasonal patterns that would `probably' mean more cold winters in Britain. Spare us the astrology, please.

Matt Ridley

Northumberland

The article contains the following paragraph:

Europe's cold winters and the warmth of the planet as a whole might even be linked. There is some evidence that the summer heat stored in the newly ice-free seas north of Siberia may induce shifts in the atmosphere's circulation, when the heat is given up to the air in subsequent autumns and winters. Those shifts might in turn encourage seasonal patterns in which the Arctic is warm and the continents below it cold, as in early 2010. Since the sea-ice area looks likely to go on shrinking, such a link, if indeed it exists, would probably mean more cold winters in Britain and much of Europe.

There is a more serious point at issue here. Without man-made global warming Britain experienced terrible winters like that of 1947 and 1963. If the Economist is right and it can still experience such winters despite (or even because of) global warming, then where exactly is the problem? How are we to distinguish the effect of climate from weather?

Observe the following chart, from Willis Eschenbach, showing the temperature record in Armagh, Northern Ireland. The dark blue line is climate change (with a healthy helping urban heat island effect). The pale blue fuzz is weather.