Satellites seek global hot spots


Where is the world's hottest place? Weather reports are too sparse to tell. But all-seeing infrared heat sensors on satellites can do the trick. A study published last week gives the 2003 honor to Queensland, Australia, with that year's high of 156.7 degrees F. (69.3 degrees C). Iran's Lut Desert claimed the title in 2004 and 2005 with highs of 154.4 and 159.3 degrees F., respectively (that's 68 and 70.7 degrees C).

The study published in Eos by David Mildrexler, Maosheng Zhao, and Steven Running at the University of Montana in Missoula illustrates a new phase in climate monitoring. Satellites that survey Earth's surface and instruments that probe beneath the sea provide a continuous overview of global climate.

The research team explains, "In a warming world where extreme [land surface temperatures] are predicted to occur more frequently ... high-resolution satellite data provide the means of keeping track of where things are heating up."

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This will help water-resource and land- management planning. The maps also illuminate the influence of land use on regional climate. The study finds, for example, that maximum temperatures in forested areas tend to be some 86 degrees F. (30 degrees C) cooler than neighboring unforested regions. Areas as disparate as the Congo's rain forest and a northeast Oregon tree farm show this effect. The satellites measure the temperature of whatever surface they see – bare ground, vegetation, or treetops. Bare ground acts like a hot plate. In a forest, trees use some of the solar heat to release water vapor, so there's less direct heating of the air from the ground.

The research team notes that the maps also highlight the importance of polar regions as "cooling engines for the Earth's atmosphere and ocean." Last summer's severe heat waves in North America and Europe illustrate this point. In the current issue of Weatherwise Magazine, geographer Jeffrey Halverson at the University of Maryland, Baltimore, describes what happened. Satellite maps show how widespread extreme heating in middle latitudes pushed the atmosphere's jet streams farther north than normal over North America. This tended to lock up the cooler northern air that would have tempered the heat waves.

Oceanographers can combine satellite measurements with data from buoys, free-floating robots, and ships to track heat flows in the upper part of the sea. John Lyman at the National Oceanographic and Atmospheric Administration laboratory in Seattle and colleagues have estimated what happened to the heat content of the upper 2,500 feet of the sea between 1993 and 2005. Their report in September showed a slight cooling between 2003 and 2005. It's a minor blip in a long-term warming trend, however. Dr. Lyman noted that "34 percent of the heat absorbed by Earth since the mid-1950s has gone into warming the ocean.... Measuring ocean temperature is really measuring the progress of global warming."

Meanwhile. Iran sees its hot spot as an opportunity. Payvand's Iran News has invited "adventurers and desert backpackers" to test their mettle in the Lut Desert, where snow-covered peaks rise above one of the hottest places on Earth.

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