 Those on the most popular routes, such as the Goûter Hut, now require all climbers to pre-book.Some tiny huts, such as the remote Eccles Hut, can also be extremely crowded during good mountaineering weather, and some climbers prefer to bivouac outside.Weather records show that since the 1960s there has been a trend of less snow at lower altitudes, whilst since the 1990s average mountain temperatures have increased more than at lower levels.