terça-feira, 2 de fevereiro de 2016

It's cold! Is global warming over?

The winter of 2010 was very cold in many parts of the U.S. And no doubt, more harsh winters are in the future.

That's weather for you.

So, what’s up with that? Is global warming slowing down? Or going backwards?

We wish that were true! But no. Many conditions affect weather. It so happens that during winter 2010, one of those conditions was a bit unusual.

The condition is the “Arctic Oscillation.”

Two drawings of Earth, one on left showing arrows around Arctic area and regions of coldest weather and storms.
The positive phase (left) has higher air pressure in the mid-latitudes than in the Arctic, making for a milder winter for the U.S. The negative phase (right) has higher air pressure over the Arctic, pushing very cold, wet air into the U.S.

Here’s what that means. Air moves from one place to another around the world because of air pressure. In some places, the air is thicker, or more dense, than in other places. We say the air pressure is higher. Air moves from areas of higher pressure to areas of lower pressure. That is wind!

The Arctic Oscillation is the movement of air back and forth between the North Pole area and the areas farther south—like down to the middle of the U.S. Sometimes the air pressure is higher in the south so the warmer air pushes north, and keeps the really cold Arctic air in the Arctic. This is called the “positive phase” of the Arctic Oscillation. Other times the air pressure is higher in the Arctic so the cold air moves south. This is called the “negative phase.” The Arctic Oscillation is a little more complicated, but this is basically how it works.

Drawing. Two circles, one on left represents are of high pressure, with arrow moving right to circle representing low pressure area.
Air in the atmosphere moves from regions of higher pressure to regions of lower pressure. This air movement is called wind.

In 2010, the Arctic Oscillation was in an extreme negative phase. That means high-pressure air over the Arctic was pushing the cold, wet air south and giving most of the U.S., Europe, and Asia a really cold, wet, and snowy winter. Yes, the far away Arctic affects our local weather.
Scientists say severe winter weather like we had in 2010 is still to be expected from time to time. That kind of weather happens even while man-made greenhouse gases build up in the atmosphere creating a long-term warming trend for the planet. When we look into our future, we definitely see a warmer world.
But don’t lose the long underwear. Frigid weather will still sometimes test our toughness. The trip to a warmer world (climate change) will have plenty of extreme hot and cold weather.

Source: NASA'S Climate Kids

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