Polar Express: Warming to Shift Storm Paths North

The Arctic has never been a pleasant place to live. But it might get worse as storm paths shift north in coming decades, possibly leaving places like Arizona and Florida drier.

Regions near both of Earth’s poles will experience more intense storms of rain and snow during the 21st Century as the planet warms, according to a new study.

The finding was based on an analysis of 15 computer climate simulations from research teams around the world and applies specifically to frontal storms, which are large-scale tempests that carry rain or snow and which can cause floods or blizzards.

Behind the shift

Frontal storms form when giant masses of warm and cold air collide, pushing against one another like two clashing titans to see who will stay and who will go. The region where they meet is called a “front.”

Making Weather Fronts are the boundaries between areas of high atmospheric pressure and low atmospheric pressure that typically bring unsettled weather. A cold front has cold air behind it that pushes abruptly underneath the warm air it encounters. As the warm air is forced upward, water vapor condenses into clouds and rain, which can sometimes be heavy along the front. A cold front, noted on weather maps by this symbol, is often characterized by quick changes and steady precipitation, followed by showery precipitation. A warm front has warm, moist air behind it that rises over the colder air it encounters. Rain may fall behind the front as the warm, rising air condenses. A warm front, noted on weather maps by this symbol, generally has a long frontal boundary -- the area where changes occur. Stationary fronts occur where warm and cold air meet but neither wins out. Unsettled weather can occur over a wide area near the frontal boundary. LEARN MORE Weather 101 All About Wind and Rain

Because warm air is less dense than cold air, the warm air mass is pushed upward by the cold one. As the warm air mass rises, its water vapor condenses into clouds laden with water droplets or ice particles that become rain or snow. The resulting storms are called frontal storms and the paths they take as they move around the globe are called “storm tracks.”

The computer simulations, called general circulation models (GCMs), show that as the century progresses, frontal storm tracks will shift poleward in both the northern and southern hemispheres by hundreds of miles. Frontal storms will become more common towards the poles and less common farther away.

“It’s not a large change but it’s something that could be noticed by people who are on either the southern or northern edge of where those types of storms tend to be,” said Jeffrey Yin, author of the study and a meteorologist at the National Center for Atmospheric Research in Colorado.

Change in the wind

Over the past century, Earth’s average temperature has risen by about 1 degree Fahrenheit.  Many scientists believe human activities are to blame and warn that temperatures may rise an additional 2-10 degrees Fahrenheit by the end of the century if steps are not taken to curb carbon dioxide and greenhouse gas emissions. Other studies predict at least a 1 degree rise by the end of this century no matter what humans might do.

Most of the warming occurs in the part of the atmosphere directly above the planet's surface, known as the troposphere.

Computer simulations, as well as satellite and weather balloon data, show that the troposphere is heating up most prominently in tropical regions near the Earth's equator. Yin believes this tropical troposphere warming is spreading in both north and south directions and that this is helping to nudge the frontal storms poleward.

The study was published recently in the journal Geophysical Research Letters.

Related change

Other types of storms, such as hurricanes, are becoming more intense as a result of global warming, according to other research. And a new study released today concludes that most parts of the planet will experience more intense storms, and more precipitation, in the coming decades.

Yin believes the same could happen with frontal storms since both hurricanes and frontal storms are affected by the amount of moisture in the air. As the atmosphere heats up over time, it can hold more moisture. This can result in more intense storms of all types, including hurricanes and frontal storms.

As the frontal storms shift poleward, they might leave in their wake regions that receive less rainfall, Yin told LiveScience. If severe enough, the affected regions could experience droughts.

In the Northern Hemisphere, it will be southern edges of the frontal storm tracks that receive less rainfall. This corresponds roughly to latitudes near the southern regions of the United States.

In the Southern Hemisphere, it will be the northern edges of the frontal storm tracks—corresponding roughly to latitudes near the northern parts of Australia—which are affected.

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Earth's Atmosphere Gravity holds gases near to the Earth to create the atmosphere, its volume composed 78 percent of nitrogen, 21 percent of oxygen, and 1 percent of argon, plus an abundance of other gases in smaller amounts. The exosphere extends up about 1,500 miles (more than three times the height of this chart). It has minimal air and constantly loses molecules to outer space. It's hottest in the thermosphere, exceeding 3,600 degrees. In the mesosphere, temperatures plummet to more than 100 degrees below zero. The stratosphere is warmer but still below freezing. The thinnest layer, the troposphere, holds about 90 percent of all the gases, sustaining life and producing weather. Water vapor in the atmosphere ranges from zero to about 4 percent.