Climate change may force airplanes to fly higher: Study

Climate change is having an increasing impact on the structure of the Earth's atmosphere, and may cause planes to fly higher to avoid turbulence, a new international study shows.

The research, published in the journal Science Advances, draws on decades of weather balloon observations and specialised satellite measurements to quantify the extent to which the top of the lowest level of the atmosphere -- called tropopause -- is rising.

The analysis of weather balloon observations alarmingly showed that the tropopause has increased in height at a steady pace since 1980: About 58 to 59 metres per decade.

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Of these, 50 to 53 metres per decade is attributable to human-induced warming of the lower atmosphere.

This trend has continued even as the influence from stratospheric temperatures has waned, demonstrating that warming in the troposphere is having an increasingly large impact.

"This is an unambiguous sign of changing atmospheric structure," said Bill Randel, a scientist at the National Center for Atmospheric Research and co-author of the new study.

The satellite observations taken since 2000 verified that the height of the tropopause has increased over the past two decades.

"These results provide independent confirmation, in addition to all the other evidence of climate change, that greenhouse gases are altering our atmosphere," Randel said.

The height of the tropopause, an atmospheric region that divides the dense and turbulent troposphere from the overlying and more stable stratosphere, ranges from about five miles above the Earth's surface at the poles to 10 miles at the equator, depending on the season.

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The location of the tropopause is of interest to commercial pilots who often fly in the lower stratosphere to avoid turbulence, and it plays a role in severe thunderstorms, whose overshooting tops sometimes drive the tropopause higher and draw down air from the stratosphere.

The steadily increasing height of the tropopause in recent decades does not significantly affect society or ecosystems, but it illustrates the wide-ranging impacts of greenhouse gas emissions.

Previous scientific studies have shown that the tropopause is rising. This was not only because of climate change, but also because of cooling in the stratosphere caused by ozone depletion gases.

These gases shrank the stratosphere through the destruction of the stratospheric ozone layer, although restrictions against their emission in more recent years have caused the atmospheric concentrations of these gases to decline.

While scientists are still not sure how a rising tropopause will influence the climate or weather, although it could force planes to fly higher in the atmosphere to avoid turbulence, they said.

"The study captures two important ways that humans are changing the atmosphere," Randel said. "The height of the tropopause is being increasingly affected by emissions of greenhouse gases even as society has successfully stabilised conditions in the stratosphere by restricting ozone-destroying chemicals."

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