Heavy weather: What climate change really means for Britain

In 1992, Tom Clarke became an apprentice gardener with the National Trust. He was a bright student, but he didn't want to be stuck in an office job: he wanted to use his hands, and he loved the outdoors. He didn't know exactly what he would be doing at the age of 35, some 17 years later, but it's safe to assume that he might have hoped to have graduated past the intricacies of lawn mowing.

Today, Clarke is the assistant head gardener at the National Trust's Trelissick Garden in Cornwall, but he has to think about mowing the lawn all the time. "In the old days, the mower would get put back in the shed for two or three months a year," he explains. "Around now, it'd be gathering dust. But now we cut grass 12 months of the year, right through the season. It's incredible really." The trend has created significant amounts of additional work for gardeners all over the country, upped repair and labour costs for organisations such as the National Trust, and knackered more than a few industrial lawnmowers. On the surface, the explanation is simple enough: milder winters mean grass that grows all year round. To Clarke, there is one clear culprit: climate change.

That's bad enough. But as we emerge from one of the bitterest cold snaps in recent memory, Tom Clarke and his colleagues are faced with a still knottier problem, and one that's simultaneously utterly concrete and infuriatingly abstract: even though the impact of climate change is so visible, even though the vast majority of world's climate scientists agree that our world is heating up, the local effects are extremely difficult to predict. To phrase the problem a different way, just when we think that we know something about the future of the climate, weather seems to be more baffling than ever.

Says Clarke: "We've had the hottest summer, the wettest summer – every other month seems to be a record breaker in a different direction. There's so much confusion. And it's hard to grasp that climate change doesn't just work in one direction. Last week it was minus seven, and this week it's 12 degrees different from that. Even a lot of quite tender plants can deal with cold weather. But the unpredictability kills them."

That makes it hard for gardeners like those at Trelissick to plan for the future. Today, they are facing a host of problems that can be attributed to global warming. Their beech trees, crucial to the classically English feel of the garden, can't put down secure roots in the soil left too damp by the heavier showers that come with warmer weather; Clarke spent last Monday hacking at two recently fallen trees with a chainsaw. The drainage for the garden's paths, laid to what seemed like worst-case-scenario specifications in the 19th century, is totally inadequate for the downpours that are more and more commonplace today. And the host of pests and plant diseases that thrive in warmer conditions are hardly helping.

But the problem of working out how carbon emissions will affect us in the future arises from the same difficulty that gives Tom Clarke such a headache. The problem is, even though experts can say with a high degree of certainty that significant warming is going to happen – and even predict what an average temperature will do over a 10-year period half a century hence – the numbers don't often mean much for our daily lives. Long-term, global trends aren't much use when you want to know whether your holiday cottage on the south coast needs a sun terrace or triple glazing.

Short-term weather events such as recent freezing winter can always override the subtler, more gradual effects of climate change, modifying them in ways that make it hard to figure out exactly what could be done to mitigate their impact. Even if we could allow for that distortion, climate scientists say, there are too many variables to make precise short-term predictions, to second guess the weather. "There are all these unknown unknowns," says Roger Street, technical director of the UK Climate Impacts Programme (UKCIP). "We understand the system better than we used to," he says, referring to the global patterns that, together, shape the weather and climate around the world, "but knowing more doesn't necessarily make things easier – it just brings to light more and more complicated things that are going on. We may actually increase the uncertainty." If you've ever wondered why, in an age when meterological websites can give you a five-day forecast tailored to your postcode, weather reports still leave have the ability to leave you stranded in flip-flops during a downpour, or sweating under jumper and jeans on freakishly hot days, this increased uncertainty may offer some level of explanation.

In spite of that frustrating fact, UKCIP is ploughing ahead with a simulation that ought to be crucial to the people scratching their heads over how best to deal with global warming. Already sufficiently delayed to have had to change its name from UKCIP08 to UKCP09, it's the first such study since 2002, and the information it provides is supposed to help businesses and institutions work out what they need to do. But the scientists running the simulation are so antsy about the uncertainty in their model that they have taken a step back. In the 2002 version, they put a firm numerical value on the effect of climate change in any given year. This time round, they're hedging their bets by offering an estimated percentage chance for each possible result.

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"More and more people are starting to use this information to adapt to the changes that are coming," says Street."We want to give people better information, and that means a better understanding of the uncertainty that lies behind it." The people he's talking about range from bridge builders to the Health and Safety executive – and private businesses. But to those getting their hands dirty, such explanations are not particularly helpful. "Five years ago," says Tom Clarke, taking refuge in a shed from the icy wind outside, "everyone was saying we'd all be growing olives down here. Well, that hasn't happened. All you seem to be able to guarantee is that things will be changeable."

This isn't the whole story, of course. While predictions of local conditions for particular days, months and even years are often unreliable, scientists have become very good at making long-term global projections of how the climate is going to behave. The model they use is remarkably simple. Climatologists take figures drawn from current weather conditions, and feed them into their model to produce a prediction for half an hour's time. Then they reinsert those figures into the model and repeat the process – and so on, until they have a decade's worth of data.

Since the models split the planet into relatively small chunks to work out these results, and since there are a great many half hours to go before the commonly used 2050 yardstick, such sums require enormous computing power. But, with the right equipment and the right figures in the first place, the results are accurate enough to be useful. "There will still be variability," says Street. "We don't predict the weather on 15 July 2051. But what we can do is talk about what the climate's likely to be in July in the 2050s."

In 2007, the Met Office made use of an innovative technique that took into account the short-term impact of oceans on the climate. It bridged the gap between long-range predictions and ordinary weather forecasts to produce a set of numbers that projected the likely climate until 2015. That decadal model warns us to expect a warm period around the world, after a few years in which global temperatures have remained flat. But on the specifics of what might happen in the UK, it wasn't so helpful. Says Mat Collins, a climate scientist at the Met Office's Hadley Centre, which produced the predictions: "There are just more competing effects at a local scale. There are more uncertainties, and the sources of the uncertainty change more."

Then there's that problem of computer capacity. Global models are commonly produced by dividing the surface of the planet into 300km cubes, and working out how each of those cubes will interact with those near it. Even that requires huge processing power – and blocks of that size are far too big to be of any use when trying to distinguish what will happen on the Cornish coast from what will happen in the Midlands.

The UKCIP projections, on the other hand, will subdivide those 300km blocks into 25km cubes, a level of detail twice that of the 2002 study. In theory, this will make it significantly more helpful to the organisations hoping to use it to plan for the future. But we still don't know what it's going to say. And even when we do, the expression of its results as a range of possibilities will simply underline the difficulty of directly connecting the effects of climate change with the weather that we'll see in the next few years. "We have a range of uncertainty," says Kay Jenkinson, communications director at UKCIP, "and the next set of information will make it more apparent what that range is. But real life being what it is, it could be that the real answer lies outside that. And we won't know what it is until we get there."

"On these very short time scales the large variations in weather just dominate the slower signal of climate change," adds Mat Collins. And he warns that whatever the report says, its data will still be hard to use. "People are going to have to use the information in a different way from what they've been expecting. It's more complete, but it won't be any easier to apply."

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This is not to say that there won't be plenty of people trying to use it. Among them will be professor Jean Emberlin, director of the National Pollen and Aerobiology Research Unit at the University of Worcester. Just as gardeners have been exasperated by an increasing workload as a result of plants growing for more of the year, Emberlin has noted an increase in problems among hay fever sufferers as summers have lengthened, allowing grass more time to flower.

Meanwhile, the tree pollen season that used to start at the beginning of April now starts at the end of March, prolonging the agony for some at the beginning of the summer. Other allergenic plants spreading to the UK mean the number of sufferers is likely to rise considerably. "It's the opposite of a vaccination," Emberlin says. "People become sensitised to it. You're exposed to increasing amounts and so you become more allergic."

Emberlin predicts an increase in the proportion of the population suffering the hay fever from a little over 20 per cent today to nearer double that within a couple of decades, and says that we need more allergists to grapple with the problem. Unfortunately, the climate data to support the case isn't entirely there. "There are all sorts of ways we could unravel long-term variations from short-term trends," she says. "But the accuracy is limited by the accuracy of the climate change predictions."

Scientists and gardeners such as Emberlin and Tom Clarke are not the only people who would like to be able to predict the future a little more accurately. Climate change will be of huge significance to property developers, and not just when they install a miniature wind farm in a millionaire's roof garden. In the long term, a hotter country will need a different sort of housing stock; in the short term, warmer weather and higher wind speeds mean that houses will need to be built with a correspondingly greater degree of flexibility.

The same is true of bridges and roads. It's nothing to worry about, says professor Steve Denton, who chairs the committee responsible for European bridge standards and advised the Highways Agency on its climate change adaptation strategy, however, "current designs in the UK use data based on historic records. And so at the moment when we design structures we don't take account for future changes in climate," or what they might mean for bridges' structural integrity. What's more, he adds, while climatologists can make estimates of temperature that are sufficient for the purposes of bridge building, they are less able to make useful estimates of changes in wind speed.

Still, although "There's no room to be complacent, there's no need to panic," Denton says cheerfully. "And this data is very powerful for decision-makers compared with what we've had in the past."

Road builders will have to factor in the changing climate when considering what kinds of concrete to use on a motorway. The road builder Tarmac is already working with UKCIP to try to figure out what the future effects will be on the surfaces it produces. And according to Tarmac director of technology Colin Loveday, the problem for the company's engineers is not so much heat as rain, which, by falling in much heavier downpours, can worm its way into cracks in the bitumen that might have remained undisturbed.

That effect will require a not-inconsiderable additional 5 per cent expenditure on new roads – and will also make old roads less stable. "There have been a number of failures on reasonably recently constructed motorways and trunk roads because the drainage isn't good enough," says Loveday. "We've changed the Highways Agency guidance, and we're sending a message out to all [those responsible for] construction standards to tell them that they need to be future-proofed." Unfortunately, the information that is needed to judge that future-proofing is not complete. According to Loveday, "The point [for UKCIP] is that if they gave a single value, they'd be liable. What they've done is to produce a range – so that you're responsible for your own risk assessment."

For something as important as the safety of a road surface, of course, manufacturers are loathe to tolerate any risk, for fear of accidents and litigation. The Health and Safety Executive is a similarly zealous organisation, and says that it will take note of the new report's conclusions when they emerge, to see what impact they may have on workplace accidents – but the organisation's Futures team, which has a specific remit to figure out what new risks might come into play in the years ahead, doesn't see the report as a useful contribution to its work. "We search for clues as to what's going to be a problem all over the place," says Peter Elwood, a member of the unit. "But the effects of climate change aren't clear in the timeframe we study. In Futures," he adds cryptically, "The one thing we don't try to do is predict the future."

Still, if figuring out whether we might all be drowned at our desks half a century hence is beyond the HSE's purview, Elwood is willing to hazard a guess at some near-term problems. "Outdoor workers are going to have a greater potential for skin cancer if they're in the sun," he says. "Employers will have to make sure that they're well covered up, and they aren't out in the heat for too long."

If you work indoors, meanwhile, you needn't think you've escaped the risks to your welfare. Whereas once the concern was making sure that offices were warm enough in the cold weather, the greater problem, Elwood says, will be keeping them cool when it's hot – without wasting too much precious energy on air conditioning units. It's just another expense for the ethical employer, but employees hoping for the occasional extra day off will be disappointed: the right to leave the workplace should the temperature exceed a certain level is nothing but an urban myth, unless you find yourself in "serious, imminent and unavoidable danger". (No, your neighbour taking his shoes off at the desk doesn't count.)

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The programme for the next few years seems clear in only one regard: the news isn't great, and the changes that we're set to encounter will reach into every area of our lives. But if the prospect of a sweltering Britain seems like a grim – if distant – one, take heart. It's not all bad. Even if we were to ignore the many things we can still do to mitigate the risks of climate change, and accept our fate, there will always be silver linings. Mike Roberts, for one, has reasons to be grateful for the coming heat: he's a winemaker, and his business looks set to grow considerably, as the British gloom that we're all so used to gives way to something closer resembling a European climate.

"We planted in 1994," Roberts says, "and we have noticed the change since then. It certainly makes grape-growing easier." The only blot on his landscape at the RidgeView Wine Estate on the Sussex Downs is a phalanx of French competitors, heading from Champagne to the south of England with their eye on the future. One small producer, Didier Pierson, has already moved across the English Channel to Hampshire, where he has started to produce sparkling wine; other champagne houses are sniffing around plots of land that cost a fraction of their equivalents back in France. But none of them has taken the plunge: the way the weather is going to change isn't yet clear enough to justify the risk.

Roberts is sure they will move in the end. "They're walking the downs now, but they'll jump in eventually," he says. "The climate there is making the drink more acidic, and that's making it harder to produce the attributes we're used to in champagne. All we need to add to our wines to compete is a bit of history."

His confidence in such uncertain times is refreshing. But not all of his colleagues working in British booze production are so optimistic. Champagne's gain is cider's loss, and apple farmers in the South-west are worried that even as stickier summers make pub-goers long for a more refreshing drink, the conditions they need will be lost.

Melvin Dickinson of Westons Cider in Herefordshire, who worked on an industry report that raised worrying questions about the future for the drink, strikes a familiar note: the great problem is not knowing exactly what will happen. "We'll get hailstorms at times when you're not expecting them, or high winds when you're not expecting them, and that can have a devastating impact on the crop," he says. "We don't know exactly how it will work, but there's no magical answer."

Pomologist, orchard keeper and fellow report author Liz Copaz adds that the great problem is the irregularity of the coming winter seasons, which won't give the trees the chance to "sleep" between fruiting periods. Says Copaz: "The worst thing probably is the unpredictability of it all – not knowing if you're going to get the sort of seasons that your trees like. If you upset the annual cycle of things what we might be getting into is a period of cropping coming every other year. We haven't seen that in modern orchards before."

By 2050, perhaps none of this will seem terribly important. Perhaps we'll all be wearing wellingtons to work and sunscreen on Christmas Day; and the only question we'll be asking about drinks is whether there's a source of clean water anywhere near our improvised huts.

But in the meantime, before that hopefully avoidable apocalypse strikes, the picture is a peculiar and hazy one. We'll be blowing our noses and reaching for the Clarityn in March and October; we'll be visiting National Trust properties that have begun to resemble colonial outposts somewhere at the furthest extremes of the British Empire; we'll be driving across wobbly bridges and crossing fingers for a day off from our dangerously hot workplaces, the better to go home and enjoy a glass of local champagne in our tropically lush back garden. At least, we might be. We still can't say for sure.

Weather Facts

38.5C on 10 August 2003, the mercury hit the highest level ever recorded in the UK, at Faversham in Kent

-26.1C the coldest temperature ever recorded in England, on 10 January 1982, in Newport, Shropshire

Winter arrived early in 1885 ; snow fell in London on 25 September that year

279mm of rain fell on Britain's wettest day, at Martinstown, Dorset, on 18 July 1955

173mph gusts of wind whipped past the Cairngorm Automatic Weather Station in the Scottish Highlands on 20 March 1986, the strongest on record