The greenhouse gas emissions produced by airplanes are not the only climate impacts associated with aviation.Four radiative forcing scenarios. Source: Lisa Bock and Ulrike Burkhardt A study conducted by German Aerospace Centre scientists points to the role of airplane contrails — condensation trails — in global warming processes.

Moisture from jet exhaust freezes into ice crystals as contrail cirrus that can persist for minutes or hours before dispersing. The heat-trapping potential of these formations alters global cloudiness and impacts radiative forcing, resulting in planetary warming. An analysis of projected increases in air traffic and associated soot emissions indicates that radiative forcing effects attributable to airplane contrails will triple from 2006 levels by the year 2050. The impact on climate due to contrail cirrus will be stronger over Northern America and Europe, the busiest air traffic areas.

Simulations published in Atmospheric Chemistry and Physics also considered possible contributions of soot emission reductions and propulsion efficiency improvements to contrail and radiative forcing control. Propulsion efficiency gains exert no impact on global radiative forcing associated with contrail cirrus. A 50% reduction in soot emissions can markedly reduce contrail cirrus optical depth and coverage, leading to a decrease in radiative forcing by about 15%. However, greater emission reductions must be realized to offset the increased contrail cirrus radiative forcing that will arise with future increases in air traffic volume.