Anthropogenic emissions of hydrogen (H 2 ) are expected to rise if H 2 energy technology is widely implemented as part of the green energy transition 1 , 2 . Although atmospheric H 2 is not radiatively active, it warms the Earth’s climate through chemical effects on methane, ozone and water vapour 1 , 2 , 3 , 4 , 5 , 6 . Predicting the atmospheric response to anthropogenic perturbations is challenging, in part because of the limited duration of the modern instrumental record 7 . Ice core measurements of H 2 can extend the observational record, providing information about anthropogenic and natural perturbations and the biogeochemical controls on H 2 levels over long timescales. However, ice core measurements of H 2 are challenging because of the high permeability of H 2 in ice 8 , 9 . Here we present an ice core record of atmospheric H 2 recovered from a Greenland ice core, spanning the past millennium. The record shows a 70–111% (2 σ ) rise in atmospheric H 2 from the pre-industrial to the modern era, consistent with increasing direct emissions from fossil fuel burning and increased atmospheric concentrations of H 2 precursors. The pre-industrial record also shows a 4–25% (2 σ ) decrease in H 2 levels during the Little Ice Age (LIA), indicating that H 2 biogeochemistry may be sensitive to climate change. The findings suggest that the sensitivity of H 2 sources and sinks to climate warming should be considered in estimates of the radiative consequences of rising anthropogenic H 2 emissions.
Patterson et al. (Wed,) studied this question.