Polar greenhouses.

Instead of heading for the beach to cool off last summer, researchers from the University of Colorado trekked up north to Alaska. Atop the Arctic soil, which is ice-free only two months a year, they built 100 mini greenhouses. Their goal: to simulate global warming and see how it might affect Arctic plants.

The greenhouses were made of Plexiglas, says researcher Marilyn Walker. The plastic lets in sunlight, but traps heat that would otherwise escape into space. A similar mechanism may be warming up our planet. But instead of plastic, scientists say, "greenhouse" gases like carbon dioxide are trapping the heat.

Scientists who want to study global warming often go to the Arctic because the effects of a climate change are likely to show up there first. That's because an increase of a few degrees in temperature can make a big difference in such an extreme climate.

For example, the average daily summer temperature in the Arctic can be as cold as 3 degrees Celsius (37 [degree] F). But inside the knee-high Plexiglas greenhouses, the temperature increased by as much as 5 [degree] C (9 [degree] F), a dramatic jump.

Plants growing in the warmed-up climate grew more and produced more seeds than those outside the greenhouse.

If the world does warm up, that may be good news for Arctic animals and people, who rely on those plants for food. But it may also be a warning sign that great changes are about to occur elsewhere on Earth. How might an increase of 5'C (9 [degree] F) change where you live?