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Published: Sunday 11 August, 2013

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Researchers have found that changes in air pressure over the past 50 years bear the fingerprint of human influence1.

This is the first report of a human effect on barometers, rather than thermometers. Most climate scientists agree that greenhouse gases produced by human activity have warmed the planet over the past cent women bags cheap ury. Nathan Gillett of the University of Victoria, Canada, and his colleagues have shown that there is also a greenhouse effect on air pressure.

Changes in air pressure could have a big effect on climate. Air pressure controls the atmospheres circulation, and therefore influences how moisture moves. Changes in circulation can alter rainfall, temperature, winds and storminess.

For instance, changes in an aircirculation pattern called the North Atlantic Oscillation have been implicated in recent increases in rainfall over Scotland, reduced rain in Spain, and a drop in the number of cold snaps in France.

These trends, and their impact on climate, could be stronger than we thought. Computer simulations of climate have underestimated the size of the change in air pressure, the researchers found.

Pressure situation The researchers studied records of air pressure at sea level dating back to 1948. They looked at three independent sets of measurements, and found that these data sets agree.

Average air pressure has risen over the past five decades in the subtropical North Atlantic Ocean, southern Europe and North Africa. In other regions, such as the poles and the North Pacific Ocean, the pressures have dropped.

These trends will tend to make winters warmer, wetter and windier in northwest Europe, says Gillett. Winters in much of western Canada and the USA will be milder, southern Europe will be drier, and Labrador and Greenland will have colder winters.

These changes, in themselves, do not prove that emissions of greenhouse gases are to blame. They could be caused by natural variations in the Earths climate.

To investigate whether human activities were the cause, Gilletts team compared their observations to four computer models of global climate. For each model, they simulated changes in greenhousegas concentrations and the amounts of dust in the atmosphere formed from sulphurcontaining gases. Dust alters climate by scattering sunlight and influencing cloud formation.

The models predictions of airp women bags cheap ressure changes matched those from the real world as long as humaninduced greenhousegas emissions were included, the researchers found. Without these emissions, the two maps did not match. women bags cheap

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