On some otherwise cloudless days, the sky over England is littered with contrails from high-flying aircraft. They are a rapid accelerator of climate change. Although the contrail lasts only half a day, during that time it causes as much global warming as the carbon dioxide released during the entire flight, although this exhaust gas survives in the atmosphere for 100 years. This surprising fact has emerged in the general debate about how to reduce emissions from air transport using new fuels, hydrogen, biofuels and electric motors. None of these potential solutions will be developed quickly, and all will be more expensive than current technology, but Whittle's lab in Cambridge believes that reducing contrails on the busiest Northern Hemisphere routes would have an immediate beneficial effect. Although contrails are common, their formation is highly dependent on atmospheric conditions. On different days and at different times, flights may produce long-lasting cloud formations or none at all. With planes traveling so fast, it is impossible for pilots to see contrails far behind them. Flying at lower altitudes would slightly increase fuel costs, but significantly reduce contrails. Scientists are trying to find a workable solution to help governments eliminate the famous white lines in the sky that are warming the planet so quickly.