Below you will find a link to the possible effects of Hydrogen in the atmosphere.
Briefly, Hydrogen can be GHG but it is short lived 10 years and we need to put strict laws and controls in place to keep the emissions to a minimum.
Using Hydrogen in a fuel cell means that we must design systems that do not leak the Hydrogen.
Hydrogen reacts with many other elements. we need to invest in technology that captures any leaked Hydrogen to keep it a a low level in the atmosphere.
See Link.
