A trip in a car increases global temperatures more than the same trip by airplane, although the flight has a more immediate impact, U.S. researchers say.

In the short run, traveling by air has a larger adverse climate impact because airplanes strongly affect short-lived warming processes at high altitudes, a study in the Journal Environmental Science & Technology says.

The study compared the impacts on global warming of different modes of transport using climate chemistry models to consider the climate effects of all long- and short-lived gases, aerosols and cloud effects resulting from transport worldwide.

The researchers concluded that in the long run the global temperature increase from a car trip would be on average higher than from a plane trip of the same distance.

However, in the first years after the journey, air travel increases global temperatures four times more than car travel.

"As planes fly at high altitudes, their impact on ozone and clouds is disproportionately high, though short lived," study lead author Dr. Jens Borken-Kleefeld said. "Although the exact magnitude is uncertain, the net effect is a strong, short-term, temperature increase."

But in the long term it was still car journeys that would have the most impact, he said.

"Car travel emits more carbon dioxide than air travel per passenger mile. As carbon dioxide remains in the atmosphere longer than the other gases, cars have a more harmful impact on climate change in the long term."