In Scotland’s Cairngorm mountains lies the UK’s third highest peak, Braeriach. Although, honestly, to call it a peak stretches the meaning of the word somewhat. Its countenance is more a rolling, hulking brute from most angles. On its north-east side, though, a huge, glacially-carved trough exists. In Gaelic this gouge in the landscape is called Garbh Choire Mòr, translated into the English tongue as big rough corrie: an apt name. In this shattered and remote corner of the Highlands, some 3,700 feet above sea level, there is at the time of writing a semi-permanent patch of old snow, nestled in against the cliff face. Called ‘the Sphinx’ after the shape of the granite rocks above it, the snow looks likely to succumb to the unusually sustained warm and sunny weather northern Scotland enjoyed this summer. At my last visit to it, on 18 September, it measured just six metres wide and barely two metres deep.For much of the population it will come as a surprise to learn that snow can and does persist on the high Scottish mountains into summer and beyond. Winter is a distant memory to most of the folk who live in our towns and cities. For walkers and Munro-baggers, however, the sight of winter’s snow persisting till summer on the high ground in the Highlands is a familiar one. But why should it matter if a certain patch of small, dirty white snow disappears? Well, the one to which I refer has been observed quietly since at least the 1700s, and its tale is a worrying one.In 1933, the Scottish Mountaineering Club wrote to The Times of London to lament the passing of the last snow in Scotland for the ‘first time in living memory’. The patch of snow to which they referred was the Sphinx. The club members did not expect to see it melt ever again; that this was a one-off. But they were to be mistaken.In the last 25 years we have seen a real reduction in the number of patches surviving from year-to-year. In fact, since that seminal event in 1933 when the Sphinx melted for the first time on record, that particular patch has disappeared a further seven times: 1959, 1996, 2003, 2006, 2017, 2018 and 2021. Readers do not have to be well versed in the vagaries of climate change study to see the direction of travel here. Our small but doughty echoes of the previous Ice Age, which ended many thousands of years ago, are starting to breathe their last.Even the language we use to describe these snows is at risk of becoming obsolete. Once-upon-a-time the adjective that best described them was perpetual; later it became semi-permanent, to then semi-perennial. But this phrase, too, will not be able to withstand the pressure put on it by the snow’s continuing disappearance. Does something that vanished entirely in 2017, 2018 and 2021 deserve the epithet of semi-perennial? This may seem a semantic consideration of little consequence in the real world but, on a planet where epochal changes have, in the past, been measured in millennia, the relatively rapid realignment of descriptive wording should be of concern to us. Small, upward deviations in temperature will put further pressure on our, for now, semi-perennial patches of snow.Snow-patch study in Scotland has become more and more reliable as the years have passed. During the 18th and 19th centuries, accounts by travellers to Scotland would comment, often in a by-the-way fashion, of seeing huge remnants of the previous winter still clinging to the cliffs and gullies of the highest peaks. One man, Colonel T Thornton, used a bed of snow during an August sporting shoot in 1796 as a handy way of keeping his drinks cold: "depositing our champaign, lime, shrub, porter in one of the large snow-drifts, which had a snow arch above a spring".As the 19th century gave way to the 20th, a new breed of mountain-goer was apt to record things a bit more diligently. Seton Gordon, that most remarkable of our far-sighted, self-taught naturalists, was known to visit and record these snows all through the first half of the 1900s. His protégé, and one of Scotland’s most esteemed ecologists, Adam Watson, carried on this work right up to his death in 2019 at 88. His observations spanned seven decades.I have been interested in patches of snow on Britain’s hills since I was nine years old, when I gazed out of my house one May morning across to seemingly unclimbable hills that lay on the horizon. On Ben Lomond, Scotland’s most southerly 3,000 ft-plus mountain, a large chunk of winter still sat immovable on its south-facing slope. Mesmerised and puzzled in equal measure, I resolved to find out more. Although, frankly, this proved rather more difficult than you might imagine. Our family were, to use the vernacular, skint. We possessed no car, and even if we did, neither of my parents drove. My investigations into this subject were limited to the books I could get from the library or from glimpses on TV shows.This childhood fascination led, many years later, to me contacting Adam Watson with some information on patches of snow I had seen and recorded in Glen Coe during autumn 1993. And, several years later, after many twists and turns, I ended up being offered by Adam lead authorship of the annual paper that appeared in the Royal Meteorological Society’s Weather journal, where individual patches of snow that survive on the very highest tops from one year to the next, were measured and counted. Adam, perhaps aware that fresh blood was needed, encouraged me to take over from him. A daunting task for someone who left school at 16 with virtually no qualifications.What have seen in the last 15 years, after decades of accurate observations, is that there is less snow than there used to be on our hills. Though we still get good years, these are coming along less often. Correspondingly fewer patches are surviving throughout the year, and even the ones that used to be regular survivors are now toiling to make it to September. We can only guess at what the situation will be like in another 20 years.The Sphinx and its ilk are barometers. Though small and little-visited, they contribute to our climate story in a manner that is way out of proportion to their diminutive size. And although our heads are turned by the disappearing Greenland ice cap, or the forest fires ravaging mainland Europe, we would do well to pay closer attention to what goes on in our own back garden, for they – surely – tell a story that is just as important, if a little less sensational.Iain Cameron is a snow patch researcher and author of the new book The Vanishing Ice – Diaries of a Scottish snow hunter (Vertebrate Publishing, Sheffield, £20).