MONTREAL: White, fine lines behind planes that look like bits of harmless cloud are anything but experts warn, who say they could have a bigger impact on the environment than CO2 emissions from the aviation sector. Condensation lines – condensation lines for short – are increasingly being studied as scientists work with industry to find technological solutions to the problem. In September, they were classified as CO2 emissions from aircraft and were the subject of a symposium in Montreal organized by the International Civil Aviation Organization, a UN agency. Contrails are clouds that form at high altitudes in cold, moist regions called ice supersaturated regions (ISSRs). When jet fuel is burned in engines, water vapor condenses on soot particles and forms ice crystals. Enough ice crystals and cirrus begin to form – high-altitude, tufty white filaments that, when formed in this way, trail behind airplanes as they cross the sky. These tracks trap some of the heat that rises from the Earth at night, preventing it from radiating back out of the atmosphere — acting as a greenhouse gas and causing warming, explains Donald Wuebbles, a professor at the University of Illinois. Contrails that stay in the sky for a few minutes aren’t too worrisome, he says. “However, if they form at night, they can last a bit longer and cause a warming effect at night,” he adds. Non-CO2 emissions could account for up to two-thirds of aviation’s global warming impact, which “gives you an idea of how important it is to think about,” Wuebbles said. And according to a 2021 study, contrails could account for as much as 57 percent of that impact — far more than C02 emissions from fuel combustion. But these emissions are short-lived compared to carbon dioxide, and their impact on global warming could be quickly reversed if solutions were found to avoid them, experts say. Not all flights create contrails – it can depend on weather conditions and the trajectory of the aircraft. At Air France, for example, just four percent of flights are responsible for about 80 percent of the impact of contrails on global warming, notes Irene Boyer-Souchet, who leads the company’s mitigation efforts. The long-term strategy is to adjust the trajectory of a fraction of the flights. Air France pilots made more than 3,000 observations over 18 months to help Meteo-France improve forecasts for risk areas so that pilots could ultimately avoid them. “The main risk is that if you think you’re avoiding an area, you might end up flying there because it’s a little bit outside the weather forecast,” Boyer-Souchet points out, illustrating the importance of fine-tuning research. American Airlines pilots conducted 70 test flights over or below risk areas based on satellite imagery, weather data, software models and AI forecasting tools. A 54 percent reduction in condensation footprint was observed along with a two percent increase in fuel economy. Accelerating the deployment of a global contrail system could reduce aviation’s climate impact by 40 percent, according to a Cambridge University report published in September. However, the more flights in the air, the more complex it would be to implement such a system, notes Boyer-Souchet, who hopes to make it a reality by 2030.
