航空機が高高度を飛行すると、適切な大気条件のもとでは、排気に含まれる水蒸気が凍結し、長時間残る飛行機雲が発生することがあります。

READING

Aircraft flying at high altitudes can sometimes produce long-lasting condensation trails when water vapor in their exhaust freezes under suitable atmospheric conditions. These trails, known as contrails, may spread and persist for hours instead of disappearing quickly. Although they look like thin clouds, their climate effect can be significant because they can reduce the amount of heat escaping from Earth's atmosphere. As a result, aviation can contribute to warming not only through carbon dioxide emissions but also through these non-CO2 effects, which may increase the sector's overall influence on the climate and complicate efforts to measure and reduce aviation-related warming.

As demand for air travel grows, the number of flights passing through areas where persistent contrails are likely to form may also increase. This could make it harder to reduce aviation's climate impact even if aircraft become more fuel-efficient or airlines cut carbon emissions in other ways. Because contrail formation depends strongly on local weather conditions, however, the effect is not the same for every flight. Some routes and altitudes may create much more warming than others, suggesting that targeted operational changes could reduce the problem without requiring major reductions in air travel or major changes to existing fleets.

One proposed response is to predict where persistent contrails are most likely and temporarily direct aircraft around those areas or to different altitudes. Avoiding high-risk zones could reduce climate effects from contrails while allowing flights to continue. However, route changes can lengthen journeys and increase fuel consumption, potentially offsetting some of the environmental benefit. Air-traffic controllers must also manage large numbers of aircraft while maintaining safety and efficiency, so widespread rerouting is not simple. Successful implementation would therefore require accurate forecasting, coordination, and careful decisions about when avoiding contrails produces a net climate benefit.