Global warning

Steve Pratt learns the difference between weather and climate – and why we can expect even more snow in the future.

IT was the coldest December for 15 years in Durham City, but it came at the end of the warmest decade since records began in 1850. Such apparently contradictory messages confuse those who find it difficult to equate blizzards, freezing temperatures and ice with a world supposedly hurtling towards global warming.

Such icy events add fuel to the fire for those claiming that global warming is all in the imagination.

Not true, says Professor Tim Burt, of Durham University’s geography department.

“You have to conclude we are at the end of an exceptionally warm period, and that’s not incompatible with weather that brings us the occasional cold snap in winter,” he says.

Chris Kilsby, professor of climate change and hydrology at Newcastle University, endorses that, while worrying that sceptics will interpret the current cold weather as evidence that scientists have got it wrong about global warming.

“It’s important to get the message out that the climate is very unstable and just because we have had a few cold weeks doesn’t mean that overall warming is not real and won’t carry on,” he says.

Other scientists point out the difference between weather and climate – weather is what happens in the short term, climate is the longterm trend.

Global warming, they say, has nothing to do with the current spell of cold and snow, which is not confined to this country. Neither have the wet summer of 2007 or recent heatwaves.

People should consider the long-term, not the fact that they are snowbound at present.

The good news is that because of global warming, extreme winters won’t happen as often as before – once every 1,100 years compared with every 183 years before 1850.

Cold winters 150 years ago were very common, says Prof Burt, but not now, which is why we get caught out when they occur.

“People’s memories are short and that’s part of the problem. They take a rather simple view and think that the weather doesn’t vary at all,”

he adds.

One cold month should not detract from the fact that last year was the 14th warmest year since records began. “The net result is still overall warm. You have to spread the message that the weather system is varied,” Prof Burt says.

“What people need to look at in terms of climate change is a longer-term perspective. We could be putting up with this and in one month be dealing with the mildest February we’ve ever had and people will have forgotten the snow,” he says.

Prof Kilsby points out that while we are experiencing a cold time, other parts of the world are unusually warm. The temperature in Newfoundland, Canada, for instance, is ten per cent higher than usual, meaning the picture that needs to be considered is a global, rather than a local, one.

“We’ve not had something like this cold spell for at least 25 years. I guess 1982 is previous marker and it could be we’ve gone beyond that.

“It’s a timeless single event, it’s not possible to look at it in terms of for and against global warming. We have to look at the longer term trends.

“I’m surprised we’ve had this and I guess most people working in climate change will admit to some surprise here, but it’s certainly not inconsistent with global warming.”

LONG-TERM weather forecasting, still in its infancy, is difficult enough, but seasonal forecasting even more so. He points out that recent showers that came off the North Sea developed very quickly and would have been “quite tricky” to pick up more than a few hours ahead.

“With longer-term seasonal forecasting, the Met Office has been quite noticeably lacking in success with the summer and winter. That’s a measure of how difficult seasonal forecasting is and reflects the chaotic nature of the weather system.”

Because long-range forecasting is relatively new, there is no way of knowing if the weather is more unpredictable than it used to be.

“My view is with climate change so far as we can only make projections of the average – temperatures are rising overall and rainfall patterns are changing. The variability around that average is very, very difficult to estimate,” says Prof Kilsby. For him and his colleagues, the reference periods in the North-East for the current winter weather are 1981-2 “which I think was colder, a more intense cold than what we’ve seen so far. This has been longer and there’s more snow. The one before that of a similar magnitude was 1962-3. So far I would say nationally that we haven’t exceeded that, but must be pretty close”.

He doesn’t underestimate the severity of the cold spell, “a remarkable event” set against a background of relatively mild winters in the Northern Hemisphere over the past 20 or 30 years.

What he feels is that we should take notice and be prepared for similar occurrences. “Certain parts of our society are very vulnerable to climate extremes,” he says, “and we have to invest in designing and maintaining our infrastructure to deal with those extremes and manage risk in a sensible way.

“While we bemoan the fact we do not have sufficient capacity to clear and grit roads, we have to balance that against the overall cost.

Maybe we need to reassess after this is over and see what measures need to be taken to change that balance.”

Global warming may even result in more snow, according to Dr Myles Allen, head of the Climate Dynamics group in the physics department at Oxford University.

“We have all heard the expression ‘too cold to snow’ and we have always expected precipitation to increase,” he says. “All the indicators still suggest that we are warming up in line with predictions.”