Research press release


Nature Communications

Climate change: Cloudy sky at night enhances Greenland plight



今回、Kristof Van Trichtたちは、衛星リモートセンシングと地上観測、地域気候モデルを組み合わせて、グリーンランド氷床の表面全体における入出射エネルギーの収支に対する雲量の影響を定量化した。ここで、Van Trichtたちは、氷だけの雲も液体を含んだ雲も氷床表面からの放射量を抑制することでグリーンランド氷床の表面を暖めるが、この氷床表面の応答が予想に反していることを明らかにした。つまり、雲が日中の温度上昇を通して氷床表面の融解を直接増やすのではなく、雲の温暖化効果は夜間が最も強く、晴天シナリオに反して、雲の存在によって氷床表面上の水分の再凍結が抑制され、年間の融解水の流出が30%以上増えるのだ。


The presence of clouds in the sky at night is capable of enhancing Greenland ice sheet meltwater runoff by more than 30% each year, according to a study published in Nature Communications this week. The finding illustrates the need for accurate cloud representations in climate models in order to better predict future contributions of the Greenland ice sheet to global sea level rise.

Melting of the Greenland ice sheet has become a dominant contributor to recent global sea level rise. The extent of this melt is in part determined by the overlying cloud cover, which affects the amount of incoming and outgoing radiation. However, different cloud types - such as ice-only or liquid-bearing clouds - can have opposing effects on how much melt is generated, and both a lack of direct measurements and differences between models have so far limited our understanding of the precise contribution of different cloud types to melting.

Kristof Van Tricht and colleagues combine satellite remote sensing, ground-based observations and a regional climate model to quantify the impact of cloud cover on the balance of incoming and outgoing energy across the entire Greenland ice sheet surface. The authors show that both ice-only and liquid-bearing clouds warm the surface of the Greenland ice sheet by limiting the amount of outgoing radiation, but that the surface response is not as expected. Rather than increasing surface melt directly through warming during the day, the clouds’ warming effect is strongest at night, when, as opposed to a clear-skies scenario, their presence acts to limit the refreezing of water on the ice sheet surface and enhances annual meltwater runoff by more than 30%.

While this study highlights the strong sensitivity of the Greenland ice sheet surface energy balance to cloud cover, it does not take into account possible warming feedback effects between the snowpack present on the surface of the ice sheet and the atmosphere above, which could complicate the cloud effect.

doi: 10.1038/ncomms10266

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