INSIDE THE RHONE GLACIER, Switzerland (Reuters) -- Tourists are flocking to Switzerland's highest peaks to see formidable Alpine glaciers melt away before their eyes -- and sometimes, onto their heads.

Emerging from a 100-metre-deep (300 feet) tunnel dug into the Rhone Glacier, the source of the Rhone River that flows to Geneva and through France, Mark Scheibner of New Jersey said concern about climate change had spurred his interest.

"It is shrinking quickly, just as we are standing here," the 48-year-old said, drops of water falling above him from the ice grotto's translucent entryway. "If anything, it makes me want to bring my daughter here to see it as soon as I can."

While it is hardly unusual for ice to melt in the summer sun, scientists are concerned that a heating-up of the world's atmosphere is causing Europe's glaciers to steadily disappear.

Swiss glaciers have lost more than 15 percent of their surface area in the last two decades, and could vanish almost entirely within a century if climate shifts are not moderated, said Max Maisch, a glaciologist from the University of Zurich.

As one of the only glaciers in Europe accessible by car, and with its man-made grotto that lets visitors walk underneath the ice mass, the Rhone Glacier has drawn many visitors looking to see for themselves how global warming is felt in the mountains.

"Tourists can observe a dying glacier here," Maisch said, standing next to the blue-tinged ice that once stretched a further 1.5 kilometers (1 mile) into the valley below.

No precise figures are available on how many people visit Switzerland's glaciers every year, because most are accessed and viewed freely, said Veronique Kanel of the Swiss tourist board.