Journal of Geophysical Research: Atmospheres

Cover image for Vol. 122 Issue 4

Impact Factor: 3.318

ISI Journal Citation Reports © Ranking: 2015: 27/184 (Geosciences Multidisciplinary)

Online ISSN: 2169-8996

Associated Title(s): Journal of Geophysical Research

Uncertainties in atmospheric mixing affect warming predictions

Uncertainties in the rates of small-scale mixing of greenhouse gases in the upper troposphere-lower stratosphere, between about 10 and 20 kilometers above Earth's surface, may be affecting predictions of how warm the Earth's surface could get in the coming decades, a new study reports. Both small-scale mixing processes and large-scale transport of atmospheric gases by winds affect the concentration of gases and hence the composition of the upper atmosphere, a region that modulates heating at the surface of the Earth. Scientists have a good understanding of the uncertainties in the rate of emission of greenhouse gases as well as those in the large-scale transport of atmospheric gases and aerosols by winds. However, they lack a similar rigorous understanding of the uncertainties in the rate of small-scale mixing, the process that smoothes out gradients in the concentrations of gases across the troposphere-stratosphere and ultimately affects climate projections. In a new study, using the atmospheric chemistry model CLaMS, Riese et al. (2012) report how uncertainties in the rate of small-scale mixing of water vapor and ozone, two of the most potent greenhouse gases with the widest disparity in spatial composition in the upper atmosphere, impact climate projections. In case of ozone, the uncertainties in mixing rates appear to affect estimates of heating (radiative effect) in the lower stratosphere, particularly in midlatitude and higher-latitude regions. In case of water vapor, the uncertainties affect estimates of heating, particularly in the tropics. The authors propose that the uncertainties in atmospheric small-scale mixing processes can result in rather large uncertainties in the simulated radiative effect of greenhouse gases, and hence in warming predictions.

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