M Cuff, Is hydrogen a climate problem?, New Scientist, 27 September 2025, p 8

In the world of atmospheric pollution, the role of hydrogen needs to be considered.   By examining ice cores immediately after extraction, researchers at the University of California, Irvine, found hydrogen concentrations to have increased from 280 to 530 parts per billion in about100 years.   Hydrogen reacts with hydroxyl radicals that would otherwise remove methane concentrations, although the effect is relatively small.