Global climate change does occur, however, and sometimes so quickly that you can watch it happening. Just look at our neighbor, Mars: within the last month, the global atmospheric temperature of Mars has increased by approximately 50 degrees Fahrenheit, according to data being received by the Thermal Emission Spectrometer (TES) on NASA's Mars Global Surveyor spacecraft.
The cause of this sudden shift is a giant dust storm that has snowballed and now has enveloped almost the entire planet, absorbing a lot of the Sun's energy in the upper atmosphere.
"It started out as a large dust storm in the southern latitudes in late June," said Arizona State University's Korrick Professor of Geology Philip Christensen, the principal investigator for TES. "The dust trapped sunlight and heated the atmosphere locally. As this warm air flowed to regions where the air was still cool it generated winds which raised more dust into the atmosphere.
"By the end of the first week in July, most of the planet was enveloped and our readings of atmospheric temperature had increased by about 30 degrees Centigrade."
TES is an instrument designed to take detailed readings of energy emissions in the infrared range (heat energy) to aid in studying Mars' geology and atmosphere. A movie showing the instrument's readings over the last month, tracking the expanding dust storm and the accompanying increase in atmospheric temperature, is available on the web at: http://tes.
"In the end, the cloaking of the entire planet with dust is probably going to cool down the surface of Mars significantly and ultimately shut this entire weather system down again," said Christensen. "It's kind of like what we imagine would happen with a nuclear winter on Earth." In fact, Christensen points out, it was another global dust storm observed on Mars in the early 1970's that gave astronomer Carl Sagan and others the idea of the kind of catastrophic climate change that might be caused by a global nuclear war.
"Mars' atmosphere is a much simpler system than Earth's," Christensen cautions, "since it is much thinner and lacks most of the water that we have in ours, trapping energy and moderating changes. "Still, it provides us with an interesting model for how global climate changes can occur, albeit much more quickly than on our planet. Nonetheless, some large scale changes here could be abrupt as well."
A NASA/JPL press release on the current martian dust storm is available at: http://www.