Reduced high-latitude land seasonality in climates with very high carbon dioxide
Henry, M; Vallis, GK
Date: 6 August 2021
Article
Journal
Journal of Climate
Publisher
American Meteorological Society
Publisher DOI
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Abstract
Observations of warm past climates and projections of future climate change show that the Arctic
warms more than the global mean, particularly during winter months. Previous work has attributed
this reduced Arctic land seasonality to the effects of sea ice or clouds. In this paper, we show that
the reduced Arctic land seasonality ...
Observations of warm past climates and projections of future climate change show that the Arctic
warms more than the global mean, particularly during winter months. Previous work has attributed
this reduced Arctic land seasonality to the effects of sea ice or clouds. In this paper, we show that
the reduced Arctic land seasonality is a robust consequence of the relatively small surface heat
capacity of land and the nonlinearity of the temperature dependence of surface longwave emission,
without recourse to other processes or feedbacks. We use a General Circulation Model (GCM) with
no clouds or sea ice and a simple representation of land. In the annual mean, the equator-to-pole
surface temperature gradient falls with increasing CO2, but this is only a near-surface phenomenon
and is not caused by the change in total meridional heat transport, which is virtually unaltered.
The high-latitude land has about twice as much warming in winter than in summer, whereas highlatitude ocean has very little seasonality in warming. A surface energy balance model shows how
the combination of the smaller surface heat capacity of land and the nonlinearity of the temperature
dependence of surface longwave emission gives rise to the reduced seasonality of the land surface.
The increase in evaporation over land also leads to winter amplification of warming over land,
although amplification still occurs without it. While changes in clouds, sea ice, and ocean heat
transport undoubtedly play a role in high-latitude warming, these results show that enhanced land
surface temperature warming in winter can happen in their absence for robust reasons.
Mathematics and Statistics
Faculty of Environment, Science and Economy
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