Scientists publishing in GRL once again affirm that in recent decades the dominant mechanism driving surface melt for the Greenland ice sheet has been downwelling shortwave radiation modulated by clearer skies (fewer clouds) and natural wind pattern changes.

Greenland’s ice melt has not been driven by “longwave heating” from greenhouse gases in the last decades – even though this has been the “prevailing hypothesis” in climate models (Wang et al., 2021).

“The day-to-day variability of normal-rate melt events is dominated by sensible heat exchange (31%) and shortwave radiation (28%). They are likely caused by katabatic winds, a gravity-driven downslope wind that can be forceful and often associated with clear skies.

“With katabatic winds occurring during clear skies, they coincide with periods of increased shortwave radiation.”

Image Source: Wang et al., 2021

A 2020 study (Hahn et al.) also concluded reduced cloud cover from 1994-2017 led to enhanced shortwave radiation (+7.3 W/m²) and drove the warming from the 1990s to mid-2000s. This shortwave cloud forcing trend is what “dominates” the melt signal for Greenland.

Image Source: Hahn et al., 2020

Another 2020 study  (Lenaerts et al.) also affirms clouds “control the Earth’s hydrological cycle”, “regulate the Earth’s climate”, and, as mentioned above, drive polar ice melt.

Image Source: Lenaerts et al., 2020

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November 4, 2021