The following is a transcript of the Weather Break radio show for Monday, January 14, 2008. The episode was written by Dr. Jon Schrage.
Last week, a series of low pressure systems called “cyclones” dumped snow across much of the western United States. In some cases, it was a LOT of snow, with Kirkwood, CA reporting over 11 FEET of snow during these storms. Now, when most people think about CA, they are picturing warm beaches and deserts, but Kirkwood is northeast of San Francisco, just south of Lake Tahoe. It’s mountainous there, and as the moist air from the Pacific flows over the lee side of the mountains, the air is forced to rise, producing condensation that falls to the ground as snow at these high altitudes. In fact, the snowiest city in the US is Truckee, CA, which averages over 203 inches of snowfall a year—that’s almost 17 FEET of snow! Some of the ski resorts in CA actually have trouble staying open in particularly wet years because the snow gets so deep that chairs on the ski lift have to be dug out of the snowdrifts!
Of course, snowfall generally does become less common the farther south you go, simply because the average temperatures are increasing. However, snow can fall at high altitudes in the tropics, and along the equator itself there are even some examples of glaciers, where the snowpack doesn’t even melt in the summer!
In the tropics, just like other parts of the world, one of the major factors that control the climate is the altitude of a location. In general, the higher a location is, the colder its climate tends to be. The reason why this happens has to due with the fact that the heat and light from the sun tend to pass THROUGH the atmosphere without heating it. The light and heat from the sun reach the ground, heating the ground. In meteorology courses, we professors always need to remind our students that the sun heats the ground, not the atmosphere. The air is then heated by the ground, either by conduction or by radiation. On a mountain top, the sun can and does heat the ground itself, but the mountaintop is surrounded by air that may be thousands of heat above the ground in the valleys. Therefore, the mountain tops remain cold. In contrast, the valleys and the lower elevations have warm ground around them on all sides, heating the surrounding air. The results are warmer temperatures at the lower elevations.
A few tropical mountains receive considerable snowfall—sometimes enough snowfall that it doesn’t melt in the cool summer season, creating glaciers. Fans of Hemmingway will immediately think of his short story The Snows of Kilimanjaro. Mt. Kilimanjaro is a volcano and it’s the highest point in Africa. At over 19,000 feet, it’s one of the highest mountains in the world. It’s also just a few degrees south of the equator in the east African nation of Tanzania. Since that’s obviously a very tropical location, you might be surprised to realize that there are glaciers on Mt. Kilimanjaro. These glaciers, however, are rapidly receding, and they will probably be completely gone in the next few decades, according to researchers. The reasons for the retreating glaciers on Mt. Kilimanjaro are not completely clear, but it could be due to either warming temperatures or decreasing precipitation in the region.
Mt. Chimborazo is the highest point in the South American nation of Ecuador, rising to over 20,500 feet. At just more than 1° south of the equator, Mt. Chimborazo is covered with glaciers, whose annual meltwater is an important source of fresh drinking water in the relatively dry provinces of Ecuador. Just like in Africa, the glaciers of Mt. Chimborazo are retreating, although the reasons why are complex and include Global Warming, El Nino, and ashfall from nearby volcanoes.
Indonesia is the nation made up of over 17,000 islands north of Australia. While most of these islands are very small, the island of New Guinea is the world’s second largest island, with about twice the area of the state of California. New Guinea is extremely tropical, with lush rain forests at low elevations. However, some of the mountains on New Guinea are more than 16,000 feet high, and they receive enough snow to form permanent glaciers as well.
Whether tropical or from a higher latitude, almost all glaciers on earth are currently retreating. It’s a matter of some debate in scientific communities about whether or not this is attributable to Global Warming. A delicate balance of precipitation and melting is necessary to maintain a glacier, and studying these factors and their role in climate is the work of a branch of earth science known as glaciology.
