The aviation industry is even worse for climate change than previously thought, with a new study revealing the damage being done by otherwise harmless contrails.
They're so bad, German researchers say, they're responsible for more warming than all aviation carbon emissions ever made - from the day the Wright brothers flew their first plane until now.
"Lots of people talk about the need to stop air traffic increasing all the time, but this is not taken that seriously," co-author Ulrike Burkhardt told New Scientist.
Aviation accounts for about 5 percent of the world's carbon emissions. Contrails - a mix of water vapour and impurities from the plane's engine left behind in the cool upper atmosphere - contribute to warming by trapping in more heat than they reflect back into space, a process known as radiative forcing.
The researchers modelled the effect contrails would have up until the year 2050, when the skies are expected to be four times busier than they are already. While cleaner fuels will help keep aviation's impact on temperatures in check, the sheer amount of cloud cover formed by contrails will wipe out any gains.
"Overall, the strong increase in radiative forcing from 2006 to 2050 due to larger air traffic volume and the shift in air traffic towards higher altitudes cannot be compensated by small reductions in radiative forcing due to changes expected from climate change, the projected reductions in reduced soot emissions and improvements in fuel efficiency," the study read.
The researchers say they may even be underestimating contrails' effect on warming by as much as 70 percent.
"It's much harder than [cutting carbon emissions]," Burkhardt told New Scientist.
The study was published in the journal Atmospheric Chemistry and Physics on Thursday.