Global warming is happening, even if it doesn't feel like it

You might think the current weather conditions are almost Siberian – and you'd be right. Britain's most prolonged spell of freezing weather since 1981 is being caused by a huge mass of intensely cold air over north-east Russia, with easterly winds sweeping its glacial temperatures across northern Europe to the UK.

And just as in the 20th century's coldest ever winter in Britain, of 1962-63 – although not on such a severe scale – the cold is being held in place over the British Isles by what is known as a "blocking anti-cyclone", a static area of high pressure over Greenland which is preventing the usual warmer, damper westerly winds from reaching us across the Atlantic.

The present situation is known as an "Omega block" as it consists of two high-pressure systems which on a weather map resemble the two arms of the Greek letter Omega – the Greenland one, and the Siberian anti-cyclone itself (whose stillness and clear skies are causing its intense cold, as much as 48C below zero in some places).

So if it is the longest cold snap for 29 years, does that prove that the idea of global warming is a non-starter? Funnily enough, it doesn't. For once you look at current meteorological conditions across the whole world, a different picture emerges.

The map on the left from the UK Met Office (it is the most recent one) shows a global picture of land surface temperature "anomalies" last week – that is, temperatures which are above or below the seasonal average. The shading from blue to black shows temperatures that are below the 1961-1990 average, while yellow through to red shows temperatures which are above it.

There, clearly marked in black, is the intense Siberian cold, with some readings of 10C below normal or even more, and you can follow the freeze westwards through Scandinavia to Britain, parts of which are shown as more than 3C below the norm.

But look at the rest of the world – in north-east America and Canada, in north Africa, across the Mediterranean, through to south-west Asia, temperatures are very much above normal – in many places by more than 5C, and in parts of northern Canada, by more than 10C.

Closer to home, while we shivered yesterday, in Madrid the temperature was 10C against a seasonal average of 9C, and in Rome it was 13C, compared to an average of 11C. The weather's natural variability means it is impossible to draw long-term conclusions about a changing climate from any single episode, be it of hot, or cold.