With small changes to trans-Atlantic flight routes, airlines could reduce their climate impact by up to 10 percent, according to a new study. These climate savings come with a 1 percent increase in operating costs for airlines.

While planes spew plenty of CO₂, they also contribute to warming by forming contrails and by altering ozone and methane levels. The relationship between contrails and climate isn’t straightforward; they generally act to warm the climate, but in some cases they can have a cooling effect. Also, emissions from aircraft flying close to or within the stratosphere have a greater effect on climate than those released at lower altitudes.

An international team of researchers looked at simulations of 400 flights across 85 routes over the North Atlantic for a representative set of summer and winter weather patterns. They found that even small routing changes, to steer clear of regions where emissions would have a large impact, would significantly reduce climate impacts with a minimal increase in cost—mostly from fuel.

The researchers say that climate-optimal routing isn’t quite ready for the real world. And cost increases may not fly in an industry with already-slim profit margins. However, they add, market-based measures that account for non-CO₂ climate impacts could offset that additional cost—and set up a win-win for the industry and the atmosphere.

Grewe V et al. Feasibility of climate-optimized air traffic routing for trans-Atlantic flights. Environmental Research Letters. 2017.