hose or from a pressure washer, which makes more snow per hour. Plans also exist for do-it-yourself snowmaking machines made out of plumbing fittings and special nozzles, or pressure washer nozzles. Pressurized air is typically supplied from standard air compressors. Volumes of snow output by home snowmakers depend on the air/water mixture, temperature, wind variations, pumping capacity, water supply, air supply, and other factors. Using a household spray bottle will not work unless temperatures are well below the freezing point of water. Extent of use By the 2009–2010 ski season, it was estimated that around 88% of ski resorts belonging to the National Ski Areas Association were using artificial snow to supplement natural snowfall. In the European Alps the proportion of ski slopes that can be covered by artificial snow varies among countries (Germany 25%, France 37%, Switzerland 53%, Austria 70%, Italy 90%). Since 1985, average aggregate temperatures in the contiguous United States for the months of November through February have consistently been above the average temperatures for those months measured between 1901 and 2000. See Figure 1. Such a trend both limits and encourages the use of artificial snow. Rising temperatures will result in greater snowmelt and decreased snowfall, thus forcing ski resorts to depend more heavily upon the use of artificial snow. However, once temperatures approach , snowmaking is not viable given the current technology. The image to the right, Photo 1, demonstrates the use of artificial snow to supplement natural snowfall. The strip of white going down the mountain is a ski slope that has been opened due to extensive use of snowmaking technology. As the use of artificial snow becomes more common and efficient, developers may seek to build new or expand existing ski resorts, as was the case with the Arizona Snowbowl ski resort. Such an action could cause significant deforestation, the loss of fragile and rare ecosystems, and cultural opposition. The high costs associated with the production of artificial snow serve as a barrier to entry for its use. It was estimated that in 2008 it cost approximately US$131,000 to purchase a snow gun and develop the necessary infrastructure. Overall, approximately US$61 million have been invested in snowmaking technology in the French Alps, US$1,005 in Austria, and US$415 in Switzerland. Furthermore, 50% of the average American ski resort's energy costs are generated by the production of artificial snow. Economics Snowmaking machines allow ski resorts