Special Seminar: John Patterson

Title: Variability in atmospheric H2 over the last 1,100 years

Abstract: Anthropogenic emissions of hydrogen (H2) are expected to rise with increasing production and use during the green energy transition.  Although atmospheric H2 is not radiatively active, it warms the Earth’s climate via chemical effects on methane, ozone, and water vapor. Predicting the atmospheric response to anthropogenic perturbations is challenging in part due to the limited duration of the modern instrumental record. Ice core measurements of H2 can greatly extend the observational record, revealing both anthropogenic and natural perturbations to atmospheric H2 levels and allowing researchers to test theories about the biogeochemical controls on H2 levels over long time scales. Ice core measurements of H2 are challenging because of the very high permeability of H2 in ice. Here we present the first ice core record of atmospheric H2 recovered from a Greenland ice core, spanning the last millennium. The record shows a 60% rise in atmospheric H2 from the preindustrial to the modern, consistent with increasing direct emissions from fossil fuel burning and increased atmospheric concentrations of H2 precursors. The preindustrial record also shows a 16% decrease in H2 levels during the Little Ice Age, indicating that H2 biogeochemistry is sensitive to climate change. The sensitivity of H2 sources and sinks to climate warming must be considered in estimates of the radiative consequences of rising anthropogenic H2 emissions.