Heavy-Water Data Aid Climate Models

Some views of Earth’s water cycle may evaporate as new atmospheric measurements reveal that existing proxy data used in climate models may be misrepresenting important ratios of H₂O and its deuterated sibling HDO in the lower atmosphere, particularly over Africa (Science 2009, 325, 1374). Because water vapor is considered the most important greenhouse gas, understanding the global hydrological cycle is key to accurate climate modeling. Isotopic ratios of water vapor provide a valuable tool to do so, notes an international research team led by Christian Frankenberg of the Netherlands Institute for Space Research. The researchers used satellite-based absorption spectroscopy to collect the first water vapor isotope data obtained in the lower troposphere, where the majority of the atmosphere’s water vapor is found. They then generated a global map showing variations in atmospheric water vapor. Last year, another team reported the first isotopic data acquired higher up in the atmosphere. “For future climate predictions, general circulation models have to be validated for their ability to correctly represent current hydrological cycles, including cloud processes, moist convection and atmospheric transport,” the researchers write.