It's a short drive from Aviemore rail station to Cairn Gorm mountain. The road winds east through an ancient forest of scots pine trees; in spring, the trees are interspersed with a bright green carpet of bilberry and juniper. When I drove that road last month, through a light fall of snowflakes, the forest floor was turning white.

The snow arrived earlier and more heavily in Scotland this season than it has for a decade. From the Canadian Rockies to the Alps, ski resorts have opened early. The world's snow-sports industry, battered in recent years by some of the warmest winters on record, has leapt on this chance to make up for lost revenue. With the pound so weak, and skiers less able to afford a trip abroad, this should all be good news for Scotland's badly battered ski industry.

I had come to the Scottish mountains for two reasons. First, I wanted to get out on this early snow, experience the small act of remembering that is the first run of the season. I also wanted to see what had happened to winter sports in the Highlands in the decades since I learned to ski there. The decline of skiing in the British isles has been oft lamented, yet people have continued skiing in the Highlands, snow permitting, albeit in ever decreasing numbers. But in 2008 two things happened that made me take the doomsayers more seriously than before: in May, the Cairn Gorm ski lift company was taken into public ownership to save it from growing debt; and in November the auditor general for Scotland announced a review of CairnGorm Mountain Ltd's greatest asset, the funicular railway that takes skiers up on to the mountain, citing "long-running difficulties" with its operation. There was even talk of it being shut down. What then would happen to skiing on Cairn Gorm, Scotland's premier ski area?

The road from Aviemore ends 2,000ft up at the funicular's lower station. The tarmac in the car park was covered with a layer of white snow when I reached it, and it was cold. In the entrance to the ticket hall I met Derek, a 60-year-old retired accountant from Kingussie who would show me round, and Mike, who runs the ski school. Together we carried our ski equipment to the brightly lit platform to catch the uphill train. At the top station, we climbed a flight of steps, put on our gloves, hats and goggles, and walked out into the wind that gusts across the plateau beneath the mountain's summit.

When Derek began skiing here with his mother and father in the 1950s, they climbed over the deer fence down by the loch and carried their skis up. They hiked upwards until lunchtime, ate their packed lunch, and then strapped on their wooden skis and skied down the mountain, and that was a day's skiing. In 1961, two days before Christmas, the first chairlift was opened on Cairn Gorm and skiing began to boom. Developers moved in. The Rank Organisation built a five-star hotel at Coylumbridge, just outside Aviemore, and in 1966 came the Aviemore Centre, a hotel and leisure complex that promised to turn a sleepy highland village into a Scottish St Moritz. Three-quarters of a million people visited the centre in its first year, many of them learning to ski for the first time on Cairn Gorm. In 1968, the Earl of Dundee declared in the House of Lords: "There is no doubt that this is one of the best skiing areas in Europe."

In the 1970s, when I first came to Aviemore, Scottish skiing was still in its heyday. There were enough skiers to support several ski schools, and the skis we hired were made by a local manufacturer, Vielhaber. The snow on the mountain was often icy in the morning and slushy in the afternoon, but there was almost always enough to carry us down to the car park. Apart from the occasional afternoon when a blizzard swept in and visibility shrank to a few feet, the skiing was good. We returned almost every year for at least a decade.

Decline set in during the 1980s. By the end of the decade it looked terminal for the Aviemore Centre: the concrete slabs that had been used to pave the resort's public spaces and walkways began to break up and sprout weeds. The dry ski slope's steel chassis had rusted and curled at the edges, threatening to carve up anyone who dared take it on. In the 1990s, much of the centre was demolished.

The cause of this decline was straightforward: a series of disastrous winters. At first people thought it was just bad luck, but the winters kept on getting milder. The ski industry's frustration can be read in the annual reports of the company that runs the lifts on the mountain. In 2002, the chairman of CairnGorm Mountain Ltd, Hamish Swan, wrote in his summary of the winter that skiing conditions were "generally poor" and it was unusually windy. The following season was "exceptionally poor, the worst for regular snow cover and skier days in the entire history of the CairnGorm ski area ... These adverse winter conditions underline the difficulties of running any weather-dependent business, but this has been exacerbated by what seems to be an accelerated rate of global climatic change ... Against this background of uncertainty, it is now self-evident that providing skiing facilities in Scotland is becoming increasingly difficult to sustain."

A plan of diversification was drawn up in an attempt to change the once-celebrated ski area to a "hospitality business with a broad range of products and services available all year". There would be corporate events and charity dinners hosted in the mountain's restaurants, and greater attention would be paid to summer visitors. The aim was to reduce the company's exposure to the inclement weather, to make it "climate-proof". In 2005, the unprecedented warming trend had, wrote Swan, had a "catastrophic impact on the whole of the Scottish ski industry". There was no doubt, he noted, that without the diversification strategy, the lift company would not have survived the year.

By 2007, and following a good skiing season in 2005-6 that bucked the trend, Swan was at his most pessimistic, reporting the worst winter on record for the Scottish ski industry with a total of only 80,000 skiers' days, compared with 660,000 in 1988. "For the first time ever," Swan noted glumly, "the lifts below the [mid station] did not operate once during the entire season because of lack of snow."

After a couple of fast runs down over good snow, with Derek acting as a guide, I warmed up in the snug twilight of the Cas Bar at the lower funicular station. I met Tania Alliod there, the spokeswoman for CairnGorm Mountain, and Ian Whitaker, the company's interim chief executive. We talked about the coming season. Early indications were promising, they said: season ticket sales had already overtaken those of the previous year, and wholesalers had reported increased activity. Even so, Alliod was no more than cautiously optimistic. If it stayed cold, there was a good chance of there being some skiing over the Christmas and new year period, which was very important in terms of revenue. Marketing was one of the difficulties of running the winter sports operation on the mountain. "We have to be very tactical, otherwise we can end up spending a lot of money up front and then [when the snow thaws] find we have nothing to offer," she said. The funicular's revenues were increasingly being made from summer and non-skiing visitors. "We used to get up to 200,000 skier visits. The old chairlift was doing 30,000-odd non-skiers. Now we get 150,000 to 155,000 non-skiing visits, so we have completely reversed the model."

Whittaker, who has been in his job as the new interim chief executive just a few weeks, learned to ski on the piste a hundred yards away as a boy while on holiday from London, more or less the same patch of mountain where I practised my first turns. After seven years working for the company, he now had the job of running it. "All the Scottish ski areas are fragile businesses," he said. Yes, he had seen reports about the impact of future warming. One of them said that there would be snow at the level of the Ptarmigan Bowl for another 60 years or so, which was long enough to see him out. "There is no point in the short term that we're going to lose skiing on Cairn Gorm full stop," he said. Nevertheless, he had noticed that conditions were more changeable than they had been. There were often big fluctuations in temperatures, and getting the best returns mean being extremely flexible, especially early in the season. "We take every opportunity to open for skiing. We're the sort of business that's used to changing daily and reacting to weather. If there's a huge snowfall we suddenly have to change all our plans. But we're totally up for that. We can turn around in 48 hours."

Many people were attracted to the mountain now simply to look at the snow, he said. Other people came in the hope of skiing, but knew there were other activities in the area if skiing was impossible. "Even in winter we see cars with two pairs of skis and two mountain bikes coming up the road. If the skiing's good they go skiing and if it isn't they go mountain biking."

When I asked about long-term plans for skiing on the mountain, the picture was less clear. Ian could not talk about whether or not the funicular had a future; I would have to put it to the company's new owners, Highlands and Islands Enterprise (HIE), the economic development agency for the region. In the meantime, in day-to-day operational terms, his team was strong and was doing a good job.

The management of the railway is at best controversial. Many people feel it should never have been built in the first place, that a cheaper way of getting up the mountain would have been far more sensible. When I called somebody from HIE for a briefing on the funicular, they were guarded. Questions were put and answered via email. Is the funicular's future 100% guaranteed for the next decade? "Since HIE's acquisition of CairnGorm Mountain, all our efforts have been deployed in working to ensure a long-term sustainable business model is in place which is fit for purpose and has the best chance of benefiting the Highland economy," was the reply. For a fuller picture I turned to a former HIE employee who has kept a close eye on the financing of the funicular, but who wished to remain anonymous. "Climate change undoubtedly is a big factor [in the financial problems of the ski area]," he said. "When I first went you could often ski down to Loch Morlich, to the woods. There was skiing down at Glenmore lodge and practice slopes down at the Hayfield. A report in about 2000 showed that the median winter snow level had moved above the car park. There must have been a steady lifting of the bottom of the snow level."

What, in his view, was likely to happen to the funicular following the auditor's review this year? Would it be closed? "The odds are if the cost of running it is not more than £1m a year or so they will say it's worth keeping it going. People will have to get used to the idea that it is a subsidised facility." The tragedy of it all, he said, was that the resort had had an opportunity to become a world leader in dealing with marginal ski conditions, but by making a number of mistakes, such as putting in an expensive funicular where an gondola would have done, and then overestimating the number of visitors they would get, they had missed their chance. "It could have been a groundbreaking project, showing how you adapt to changing climate," he said.

Beyond the mountain, the programme to wean the local economy off winter sports is now well developed. Almost 4,000 jobs in Badenoch and Strathspey depend on tourism, which was worth £142m last year. The plan has been to retain as much of the snow-sports market as possible while promoting the area as a centre for other outdoor activities, from canoeing and mountain biking to family walks and ice-climbing. According to Alan Rankin, chief executive of Aviemore and the Cairngorms Destination Management, the area is well positioned. "While we have seen skier numbers reduce quite severely over the past 10 or 20 years, overall visitor numbers are being held because of the broad offering," he said.

Travelling around Strathspey, I find clear evidence of the diversification programme. Where the old Coylumbridge hotel had an outdoor winter ice rink, the Coylumbridge Hilton, as it now is, has a vast indoor play-shed. The Aviemore Centre has been redeveloped as a smart conferencing and leisure facility. Out has gone the old dry ski slope, the ice rink and the ski shops, and in have come an indoor pool, a gym and a shop specialising in designer labels. The once small Landmark Centre at Carrbridge has become an upmarket theme park, with woodland trails, rock climbing, log flumes and a steam-power sawmill. Tens of millions of pounds have been spent in the area, and it is looking wealthier and happier than it did in the run-down 1990s. Skiers may not be coming in the quantities they once did, but other visitors are.

It would be wrong to write off skiing on Cairn Gorm just yet, but it is reasonable to ask how long it has got. Aside from Whitaker's stated belief that there will still be skiing at the top of the mountain in 60 years - which, given recent winter seasons, seems optimistic - few people are willing or able to put a timescale on it. Several Scottish skiers relate to me the hope that the increased flow of cold water from the Arctic will diminish or even shut down the gulf stream, which, they argue, could lead to a much colder climate and a snow bonanza. But when I put that to Matt Collins at the Met Office's Hadley Centre for climate change research, he swiftly shot the theory down. "Our current models tend to show that the greenhouse gases win out over the weakening of the gulf stream, so you still get a net warming effect. We expect that the ski season will get shorter and the lower resorts will have a much shorter season. The snow line migrates upwards."

Of course, this isn't just a Scottish or a British problem. The livelihoods of lower-lying ski resorts across Europe are precarious, and even high-altitude resorts are making plans to offer activities that don't require snow. A survey of the future of Alpine skiing in 2006 found that a 2C rise in temperature meant that some 40% of current snow-reliable resorts would become unreliable, and that the Alps were warming twice as fast as the planetary average.

There are, it is true, more pressing reasons to try to minimise climate change than to protect a leisure pursuit, however wonderful that pursuit may be. But I have witnessed no clearer indications of climate change than the increasing scarcity of snow on this very special mountain, Cairn Gorm.

We decided on one more run down from the top, Derek and I. We walked up behind the Ptarmigan station and clipped into our bindings, then he shot off down the traverse towards the Corrie Cas. I followed, struggling to keep up, watching his bright yellow ski jacket disappear into the white of the cloud and the wind-blown snow ahead.

• The Snow Tourist by Charlie English is published by Portobello Books. snowtourist.co.uk