Atmospheric H2 variability over the past 1,100 years

Abstract

Anthropogenic emissions of hydrogen (H2) are expected to rise if H2 energy technology is widely implemented as part of the green energy transition1,2. Although atmospheric H2 is not radiatively active, it warms the Earth’s climate through chemical effects on methane, ozone and water vapour1–6. Predicting the atmospheric response to anthropogenic perturbations is challenging, in part because of the limited duration of the modern instrumental record7. Ice core measurements of H2 can extend the observational record, providing information about anthropogenic and natural perturbations and the biogeochemical controls on H2 levels over long timescales. However, ice core measurements of H2 are challenging because of the high permeability of H2 in ice8,9. Here we present an ice core record of atmospheric H2 recovered from a Greenland ice core, spanning the past millennium. The record shows a 70–111% (2σ) rise in atmospheric H2 from the pre-industrial to the modern era, consistent with increasing direct emissions from fossil fuel burning and increased atmospheric concentrations of H2 precursors. The pre-industrial record also shows a 4–25% (2σ) decrease in H2 levels during the Little Ice Age (LIA), indicating that H2 biogeochemistry may be sensitive to climate change. The findings suggest that the sensitivity of H2 sources and sinks to climate warming should be considered in estimates of the radiative consequences of rising anthropogenic H2 emissions. Analysis of the atmospheric H2 variability over the past millennium suggests that the sensitivity of H2 to climate change should be considered in estimates of the radiative consequences of rising anthropogenic H2 emissions.