The last glacier in Scotland melted hundreds of years ago. But the towering mountains still harbor nearly-perpetual “snow patches”—remnants of winter snowfall that can last all summer long. And a small cadre of mountaineers actually keeps track of those patches. But as the climate changes, the snow isn't going to stick around for long.

As Simon Usborne at the Financial Times reports, as of this week, only two patches remain and the oldest of these patches, a 11-year-old spot dubbed "The Sphinx," is expected to disappear over the next couple of days. Located at Garbh Choire Mór​ on Braeriach, Britian’s third-tallest mountain, the disappearance of the patch will mark the first time in 11 years that Britain will be completely snowless—only the sixth time that’s likely happened in 300 years.

In a typical year, there are dozens of snow patches that stick through the summer on north-facing slopes in the Cairngorms and Ben Nevis mountain ranges in the Scottish Highlands, home to the island’s highest peaks, Usborne reports. Some years, the patches are just over 300-feet across and several feet deep.

“These patches assume more or less the same shape each year,” Iain Cameron, Scotland’s most dedicated patch watcher tells Usborne. “But as each year elapses, the more elderly they become and you also know that at some point you’re going to visit and they’re not going to be there.”

At this time of year, there are typically 50-100 patches left in the mountains, according to Murdo MacLeod at The Guardian. Last year, in mid-September there were 82 still holding on and in 2015, which MacLeod notes was a particularly unusual year, there was an astounding 678 patches. The Sphinx patch almost always survives the summer, and is eventually refreshed by winter snow, which usually begins around October.

But as Cameron tells Martyn Mclaughlin at The Scotsman, it isn’t high temperatures that are decimating the snow patches this year. It is the light snow that fell last winter. “It was an extraordinarily dry winter and not much snow fell at all,” he says. “The Scottish ski centers all reported very poor skier day numbers and it’s no coincidence that the patches of snow are correspondingly smaller.”

The year 1933 marked the first time the Sphinx completely melted since record keeping began in 1840. At the time, it was so alarming that the Scottish Mountaineering Club wrote a letter to the Times of London to record the unusual event, reports Usborne

Since then, however, the Spinx melted again in 1959, 1996, 2003 and 2006. “The rate of melt of these patches has accelerated in the past 20 years,” Cameron tells Usborne. “There’s no question that snow is not lasting as long as it used to.” This reduction in snowfall is one of the many predicted effects of climate change—and is expected to only get worse in coming years.

MacLeod reports that Cameron, along with a small group of volunteer "snow patchers," are now the official monitors of the icy bits, keeping track of the snow chunks in out of the way canyons and cliff sides in the mountains. Each year, the group submits an annual snow patch survey to the Royal Meteorological Society.

Steven McKenzie at the BBC reports that the second surviving patch is on the mountain Aonach Beag and is also expected to completely disappear this week. Ben Nevis, the highest mountain on the Island, was declared snow-free for the first time in 11 years in August.

Cameron tells MacLeod that he is camping out near the Sphinx this week, hoping to be the first person to record the rare disappearance of the snow.