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Increased Arctic cloud longwave emissivity associated with pollution from mid-latitudes


There is consensus among climate models that Arctic climate is particularly sensitive to anthropogenic greenhouse gases and that, over the next century, Arctic surface temperatures are projected to rise at a rate about twice the global mean1. The response of Arctic surface temperatures to greenhouse gas thermal emission is modified by Northern Hemisphere synoptic meteorology and local radiative processes2,3,4. Aerosols may play a contributing factor through changes to cloud radiative properties. Here we evaluate a previously suggested contribution of anthropogenic aerosols to cloud emission and surface temperatures in the Arctic5,6,7,8. Using four years of ground-based aerosol and radiation measurements obtained near Barrow, Alaska, we show that, where thin water clouds and pollution are coincident, there is an increase in cloud longwave emissivity resulting from elevated haze levels. This results in an estimated surface warming under cloudy skies of between 3.3 and 5.2 W m-2 or 1 and 1.6 °C. Arctic climate is closely tied to cloud longwave emission2,4,9, but feedback mechanisms in the system are complex10 and the actual climate response to the described sensitivity remains to be evaluated.

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Figure 1: Sensitivity of cloud LW emissivity to changes in droplet number concentration for fixed water path, SLW = (d ɛ /d N)W.
Figure 2: Surface-based observations of Arctic pollution, clouds, and their radiative properties, made near Barrow, Alaska.


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This work was supported by the National Science Foundation. J. Ogren provided CMDL data. V. Walden and A. Mahesh provided assistance with retrieval development. Author Contributions Both authors contributed equally to this manuscript.

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Correspondence to Timothy J. Garrett.

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Garrett, T., Zhao, C. Increased Arctic cloud longwave emissivity associated with pollution from mid-latitudes. Nature 440, 787–789 (2006).

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