CLIMATE CHANGE

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	What Drives Climate Change?
	Solar input The sun's energy, after traveling 93 million miles to get to Earth, hits the upper atmosphere at about the intensity of three 100-watt bulbs per square yard. A third is reflected back into space, two thirds warms the planet and drives its weather engine.
	The atmosphere Earth gets its liveable temperature (on average 59 degrees Fahrenheit) thanks to a delicate balance of gases that create a "greenhouse" effect by trapping heat inside the atmosphere. Greenhouse gases -- water vapour, carbon dioxide, methane, nitrous oxide, and others -- absorb heat energy, then re-radiate a portion of it back to the surface.
	The oceans Covering two thirds of the planet, oceans are the key source of moisture in the air and they store heat efficiently, transporting it thousands of miles. The oceans and marine life also consume huge amounts of carbon dioxide.
	The water cycle Higher air temperatures can increase water evaporation and melting of ice. And while water vapour is the most potent greenhouse gas, clouds also affect evaporation, creating a cooling effect.
	Clouds They both cool Earth by reflecting solar energy and warm Earth by trapping heat being radiated up from the surface.
	Ice and snow The whiteness of ice and snow reflects heat out, cooling the planet. When ice melts into the sea, that drives heat from the ocean. Northern Hemisphere snow cover has declined 10 percent in two decades, but no significant melting of the Antarctic ice sheet has been detected.
	Land surface Mountain ranges can block clouds, creating ‘dry’ shadows downwind. Sloping land allows more water runoff, leaving the land and air drier. A tropical forest will soak up carbon dioxide, but once cleared for cattle ranching, the same land becomes a source of methane, a greenhouse gas.
	Human influences Humans might be magnifying warming by adding to the greenhouse gases naturally present in the atmosphere. Fuel use is the chief cause of rising carbon dioxide levels. On the other hand, humans create temporary, localized cooling effects through the use of aerosols, such as smoke and sulphates from industry, which reflect sunlight away from Earth.