London, Jun 28 (IANS): Researchers have found that contrails - the white lines that airplanes leave behind in the sky - are a major cause of global warming and their impact on the climate was expected to triple by 2050.

The study, published on Thursday in the journal Atmospheric Chemistry and Physics, found that due to increased air traffic activity, contrail-induced warming was expected to be thrice larger in 2050 than what it was in 2006.

Contrails change global cloudiness which creates an imbalance in the Earth's radiation budget - called radiative forcing - that results in warming of the planet. The larger this radiative forcing, the more significant the climate impact.

Noting that non-carbon dioxide climate impacts could not be neglected, researchers said that the increase was predicted to be faster than the rise in carbon dioxide radiative forcing since expected fuel efficiency measures would reduce carbon dioxide emissions.

The increase in contrail radiative forcing was due to air traffic growth and a shift of flight routes to higher altitudes. According to researchers, cleaner aircraft emissions would solve part of the problem.

In 2005, air traffic made up about five per cent of all anthropogenic radiative forcing, with contrails being the largest contributor to aviation's climate impact.

"It is important to recognise the significant impact of non-carbon dioxide emissions such as contrails on climate and to take those effects into consideration when setting up emission trading systems or schemes like the Corsia agreement," said the study's lead author Lisa Bock from the German Aerospace Center.

Corsia - UN's scheme to offset air traffic carbon emissions from 2020 - ignores the non-carbon dioxide climate impacts of aviation.