"Plane tracks" in cirrus clouds

Determining the effects of aircraft emissions on cirrus clouds already present in the atmosphere has proven to be challenging. Quantifying any such effects is necessary if we are to properly account for the influence of aviation on climate. Here we quantify the effect of aircraft on the optical thickness of already-existing cirrus clouds by matching actual aircraft flight tracks to satellite lidar measurements. We show that there are systematic, statistically significant increases in normalized cirrus cloud optical thickness inside mid-latitude flight corridors compared with adjacent areas immediately outside the corridors.