Leading article: The cold offers no comfort on climate change

Climate scientists frequently point out that the weather and the climate are not the same thing. Indeed, they often sum up the difference by saying that the climate is what we expect and the weather it what we get. The climate operates over long periods, often too long for us to remember with any accuracy without the help of good-quality records. The weather, meanwhile, is very much the here and now and is, as a result, at the forefront of our minds, which is the case now.

Two bitterly cold winters on the run seems like a climatic trend, but in fact for scientists they do not (yet) form a pattern that indicates some kind of aberration beyond the natural variation we expect from such a chaotic phenomenon as the global climate system.

For a start, as the Meteorological Office in London points out, what we are seeing in Britain and western Europe is a regional rather than a global effect. As Britain freezes in sub-zero temperatures, Greenland and northern Canada appear to be experiencing warmer than average weather, thanks to some extent by the diversion of the westerly winds that usually bring us damp, mild weather at this time of the year.

Other phenomena may also be playing a role. For instance, Met Office scientists say that the activity of the "La Nina" ocean current in the tropical Pacific Ocean appears to be at a 20-year high. In addition, the longer-term oscillation between low and high pressure systems in the North Atlantic appears to be entering a phase last seen in the 1960s, when we also experienced cold winters.

Such considerations underline the fundamentally complex nature of the global climate system. But they do not negate the fact that global temperatures unequivocally show that the world is getting warmer.

Global warming, despite what we may feel when we step outside, is a reality. It may be difficult, but what is important to keep in mind is the effect that it will have both in the long term, and on the world as a whole. Climate change will be with us long after we've forgotten this little local difficulty called a cold winter.