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Northland: the climate of a world with a hemispheric continent and a hemispheric ocean
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  • Marysa Lague,
  • Marianne Pietschnig,
  • Sarah Ragen,
  • Timothy Smith,
  • David Battisti
Marysa Lague
University of California Berkeley

Corresponding Author:mlague@berkeley.edu

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Marianne Pietschnig
University of Exeter
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Sarah Ragen
University of Washington
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Timothy Smith
University of Texas at Austin
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David Battisti
University of Washington
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Join us in an exploration of the climate of Northland, a world where the entire northern hemisphere is covered by a continent, and the entire southern hemisphere is covered by an ocean! On the continent, we will visit the seasonally moist tropics, the subtropical desert, and the Great Northern Swamp. We explore the interplay between water, energy, land, ocean, and atmosphere in this idealized climate model study. We find that the presence of a continent greatly increases the poleward extend of the ITCZ over both the land and ocean hemispheres compared to an aquaplanet, as a result of hemispheric energy imbalances introduced by (a) the small heat capacity of land and (b) large reductions in atmospheric water vapor (and thus reduced longwave trapping) over the continent. A combination of moisture transport from the tropics and local water recycling results in a polar swamp over the continent. We explore how the climate state responds to changes in the albedo and evaporative resistance of the continent. While making the land surface darker leads to warming, we find that decreasing evaporation from the land surface leads to global-scale cooling. This is in contrast to past studies, where reduced terrestrial evaporation leads to warming as a result of suppressed evaporative cooling of the land surface. In the case of Northland, the lack of an ocean to provide water to the northern hemisphere means that decreasing land evaporation leads to large reductions in water vapor over the northern hemisphere, in turn reducing strength of the greenhouse effect, resulting in cooling of near-surface air temperatures. This cooling signal is strongest over the continent, but cools air temperatures over the ocean hemisphere as well. We hypothesize that a threshold exists in the temperature response to reduced terrestrial evaporation: for small decreases in evaporation, reduced latent cooling dominates and near-surface temperatures warm, while for large decreases in evaporation, reduced longwave trapping from reduced atmospheric water vapor dominate, cooling near-surface temperatures. Through this idealized study of a hypothetical, Earth-like planet, we gain valuable insight into the connections between water, energy, land surface properties, and continental distribution in controlling global-scale climate.