Ships release invisible contrails that slightly cool the climate

Streaks of invisible air pollution from the world’s shipping industry, which are unseen on satellite imagery, are changing the reflectivity of clouds. This means clouds exposed to air pollution from all sorts of sources may reflect more of the sun’s light and heat than we thought, which will have to be taken into account for future climate models. The effect of this air pollution doesn’t negate the effect of the greenhouse gases also released, however.

Clouds play a complex role in the climate. Depending on how high they float in the atmosphere and their composition, they can either contribute to or detract from global warming. Understanding their interactions with the environment is crucial for accurate climate models.

Pollution from aerosols – fine particles suspended in air – influences the formation and properties of clouds. The climate warming role of greenhouse gases in shipping emissions is well established, but less is known about the aerosols. Previous studies looking at the aerosols from ship funnels have used satellite imagery to assess their effect on clouds – some are affected, but many more clouds appeared unaffected.