Airplane contrails are a tricky, and surprising, contributor to global warming 

 Commercial airplanes have made strides in reducing carbon emissions, but it turns out the exhaust clouds trailing behind them can have long-term impacts on the environment.  

https://cdn.mos.cms.futurecdn.net/VkbN8hkCLg7G727kPzVgqj.jpg

https://www.space.com/modern-airplane-contrails-impact-global-warming