Hydrogen is often seen as a possible clean fuel for trucks, planes, power plants and industrial processes because it combusts cleanly, leaving behind only water, and can be produced using renewable electricity. But if too much hydrogen leaks along the supply chain, a new Princeton and NOAA study finds, it may have serious unintended effects in the atmosphere and for global warming.

The new study models various scenarios and the effect of hydrogen in the atmosphere based on how the hydrogen is produced (with renewable electricity or from natural gas) and how much of it leaks. The scientists found that, because of a unique reaction between atmospheric gases, at certain leakage rates adding hydrogen to the atmosphere prolongs the life of existing atmospheric methane, a potent greenhouse gas. On average, methane disappears in around 10 years, but would last longer with the additional hydrogen emissions.

The researchers, including Princeton engineers Matteo Bernard Bertagni and Amilcare Porporato, say their study allows developers and governments to be proactive as they consider ways to design and implement hydrogen infrastructure.

“We have a lot to learn so the switch to hydrogen, a seemingly clean fuel, doesn’t create new environmental challenges,” says Porporato.