Snow Line, the line, usually in mountains, above which there is permanent snow. Below the line, temperatures are sufficiently high during the warmest months to melt the covering of snow. Virtually nowhere is the snow line in a fixed position, for the altitude at which it occurs varies with the depth of the annual snowfall, exposure to the sun, steepness of the slope, and the direction and velocity of the wind. In general, the snow line decreases in elevation from the equatorial regions, where it lies as high as 20,000 feet (6,000 m), to sea level near the poles.
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Much of the ice has melted, and the woolly mammoths are long gone. But could we still be in an ice age and headed for another?