trail difficulty rating, other factors come into play. A trail will be rated by its most difficult part, even if the rest of the trail is easy. Ski resorts assign ratings to their own trails, rating a trail compared only with other trails at that resort. Also considered are width of the trail, sharpest turns, terrain roughness, and whether the resort regularly grooms the trail. Safety In 2014, there were more than 114,000 alpine skiing-related injuries treated in hospitals, doctor's offices, and emergency rooms. The most common types of ski injuries are those of the knee, head, neck and shoulder area, hands and back. Ski helmets are highly recommended by professionals as well as doctors. Head injuries caused in skiing can lead to death or permanent brain damage. In alpine skiing, for every 1000 people skiing in a day, on average between two and four will require medical attention. Most accidents are the result of user error leading to an isolated fall. Learning how to fall correctly and safely can reduce the risk of injury. Health According to a 2004 Harvard Medical School study, alpine skiing burns between 360 and 532 calories per hour. Climate change Winter season lengths are projected to decline at ski areas across North America and Europe due to the effects of global warming. In the United States, winter season lengths are projected to decline by more than 50 percent by 2050 and by 80 percent by 2090 if greenhouse gas emissions continue at current rates. About half of the 103 ski resorts in the Northeastern United States operating in 2012 may not be able to maintain an economically viable ski season by 2050. In Europe, half of the glacial ice in the Alps has melted and the European Geosciences Union projects snowpack in the mountains could decline 70 percent by 2100 (however, if humans manage to keep global warming below 2 °C, the snow-cover reduction would be limited to 30 percent by 2100). See also Para-alpine skiing Skiboarding References External links Alpine Canada Alpin – Alpine Canada Alpin, National Governing Body for Ski Racing within Canada U.S. Ski and Snowboard Association – The National Governing Body for Ski Racing U.S. Ski Team – Bio information and stories on U.S. elite athletes Retro Ski – ski history Alpine Ski Database Colorado Ski Museum Winter Olympic sports Snow sports