What is the evidence supporting global warming?

More and more scientists are becoming convinced that we are seeing an increasingly swift transition toward a warmer climate on Earth. Data is constantly being collected by meteorologists, environmentalists, and other scientists working in labs and out in the field. While there is no definitive proof that will assuage all doubters, the evidence is mounting. Below are some of the reasons why the fear of global warming is gaining ground.

Record-breaking temperatures—Cities around the world have been recording high temperatures in the last decade or two that have exceeded all previous records.

Drought and rain pattern changes—Dry areas are becoming drier, and wet areas are becoming wetter; floods are becoming more frequent, as rivers fill with record levels of water. For example, the American Midwest and Great Plains states have seen significant increases in flooding in recent years (though part of this can be blamed on farming and levee activities). The Northwest is

Global warming negatively impacts coral reefs, such as this reef near Chuuk, Micronesia. Warming waters kill off corals, causing a

Global warming negatively impacts coral reefs, such as this reef near Chuuk, Micronesia. Warming waters kill off corals, causing a "bleaching" effect that destroys rich habitat. (photo by Dwayne Meadows, NOAA/NMFS/OPR)

also seeing much more rain, while the southwest and, especially, southeastern states have been experiencing extended droughts.

More extreme weather—Some—though certainly not all—scientists feel that Hurricane and tornado activity appears to be on the rise, with the United States and Southeast Asia being particularly hard hit. One of the worst years of recent memory, 2005, included the devastating Hurricane Katrina that destroyed New Orleans and other Gulf Coast cities. Climatologists noted that there had been a lull in hurricanes during the 1970s and 1980s, but since 1995 there has been a significant upswing. Between 1995 and 2005, nine of the hurricane seasons had above normal incidents of storms.

Warming oceans, coral reef bleaching—There is widespread and undisputed evidence that coral reefs around the globe are in trouble. Although coral reefs occur in tropical, warm waters, too much warming will kill coral; first, because the organisms simply don't tolerate such temperatures, and second because warmer water is not able to maintain as much dissolved calcium, which coral need to survive. When corals die, the vivid colors the tiny animals lend reefs disappear; hence the term "bleaching."

Melting glaciers—The most commonly used piece of evidence for global warming has been the changes seen in glaciers, especially in the North, but also in Antarctica and on mountaintops around the world. Photographs have shown, for example, that Greenland glaciers are retreating at a rate of about 100 feet (30 meters) per day. In Antarctica, the Larsen Ice Shelf, covering an area roughly the size of Rhode Island, broke off the mainland. Meanwhile, the glacier on top of Mount Kilimanjaro in Tanzania is quickly melting, and scientists speculate there will be no more snow on the mountain by 2020.

Is global warming causing the world's glaciers to melt?

Many scientists believe that greenhouse gases are directly causing glaciers in all parts of the world to melt and recede at an unprecedented rate. It is thought that by 2030 there will be no glaciers in Glacier National Park in Montana. In East Africa, Mt. Kenya's Lewis Glacier in Kenya has lost 40 percent of its size in just the last 25 years.

What is the ICESat mission?

ICESat (short for Ice, Cloud, and Land Elevation Satellite) is a satellite launched by NASA on January 12, 2003, to collect data on everything from land topography and vegetation to information on aerosol levels. On board is a single monitoring device called the Geoscience Laser Altimeter System (GLAS). One of the chief missions of ICESat, however, is to find out how the planet's ice sheets are changing.

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