In the 1980s, the U.S. Geological Survey began a more systematic study of the remaining glaciers, which continues to the present day. By 2010, 37 glaciers remained, but only 25 of these were considered to be "active glaciers" of at least 25 acres (0.10 km2) in area.[46] If the current warming trend continues, all of the remaining glaciers in the park will be gone by 2020.[44] This glacier retreat follows a worldwide pattern that has accelerated even more since 1980. Without a major climatic change in which cooler and moister weather returns and persists, the mass balance, which is the accumulation rate versus the ablation (melting) rate of glaciers, will continue to be negative and the glaciers will eventually disappear, leaving behind only barren rock.[47]

After the end of the Little Ice Age in 1850, the glaciers in the park retreated moderately until the 1910s. Between 1917 and 1941, the retreat rate accelerated and was as high as 330 feet (100 m) a year for some glaciers.[46] A slight cooling trend from the 1940s until 1979, helped to slow the rate of retreat and in a few examples some glaciers even advanced a few tens of meters. However, during the 1980s, the glaciers in the park began a steady period of loss of glacial ice, which continues as of 2010. In 1850, the glaciers in the region near Blackfoot and Jackson Glaciers covered 5,337 acres (21.6 km2), but by 1979, the same region of the park had glacier ice covering only 1,828 acres (7.4 km2). Between 1850 and 1979, 73% of the glacial ice had melted away.[48] At the time the park was created, Jackson Glacier was part of Blackfoot Glacier, but the two have separated into two glaciers since.[49]

The impact of glacier retreat on the park's ecosystems is not fully known, but cold water dependent plant and animal species could suffer due to a loss of habitat. Reduced seasonal melting of glacial ice may also affect stream flow during the dry summer and fall seasons, reducing water table levels and increasing the risk of forest fires. The loss of glaciers will also reduce the aesthetic visual appeal that glaciers provide to visitors.[48]

Climate[edit source | edit]

The Big Drift covering the Going-to-the-Sun Road as photographed on March 23, 2006

As the park spans the Continental Divide, and has more than 7,000 feet (2,100 m) in elevation variance, many climates and microclimates are found in the park. As with other alpine systems, average temperature usually drop as elevation increases.[50] The western side of the park, in the Pacific watershed, has a milder and wetter climate. Precipitation is greatest during the winter and spring averaging 2 to 3 inches (50 to 80 mm) per month. Snowfall can occur at any time of the year, even in the summer, and especially at higher altitudes. The winter can bring prolonged cold waves, especially on the eastern side of the Continental Divide. Snowfalls are significant over the course of the winter, with the largest accumulation occurring in the west. During the tourist season daytime high temperatures average 60 to 70 °F (15 to 20 °C), and nighttime lows usually drop into the 40 °F (5 °C) range. Temperatures in the high country may be much cooler. In the lower western valleys, daytime highs in the summer may reach 90 °F (30 °C).[51]

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