Sensitivity of sea ice to wind-stress and radiative forcing since 1500: a model study of the Little Ice Age and beyond |
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| Authors: | Jan Sedlá?ek Lawrence A Mysak |
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| Institution: | (1) Earth System Modelling Group, Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, QC, H3A 2K6, Canada |
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| Abstract: | Three different reconstructed wind-stress fields which take into account variations of the North Atlantic Oscillation, one
general circulation model wind-stress field, and three radiative forcings (volcanic activity, insolation changes and greenhouse
gas changes) are used with the UVic Earth System Climate Model to simulate the surface air temperature, the sea-ice cover,
and the Atlantic meridional overturning circulation (AMOC) since 1500, a period which includes the Little Ice Age (LIA). The
simulated Northern Hemisphere surface air temperature, used for model validation, agrees well with several temperature reconstructions.
The simulated sea-ice cover in each hemisphere responds quite differently to the forcings. In the Northern Hemisphere, the
simulated sea-ice area and volume during the LIA are larger than the present-day area and volume. The wind-driven changes
in sea-ice area are about twice as large as those due to thermodynamic (i.e., radiative) forcing. For the sea-ice volume,
changes due to wind forcing and thermodynamics are of similar magnitude. Before 1850, the simulations suggest that volcanic
activity was mainly responsible for the thermodynamically produced area and volume changes, while after 1900 the slow greenhouse
gas increase was the main driver of the sea-ice changes. Changes in insolation have a small effect on the sea ice throughout
the integration period. The export of the thicker sea ice during the LIA has no significant effect on the maximum strength
of the AMOC. A more important process in altering the maximum strength of the AMOC and the sea-ice thickness is the wind-driven
northward ocean heat transport. In the Southern Hemisphere, there are no visible long-term trends in the simulated sea-ice
area or volume since 1500. The wind-driven changes are roughly four times larger than those due to radiative forcing. Prior
to 1800, all the radiative forcings could have contributed to the thermodynamically driven changes in area and volume. In
the 1800s the volcanic forcing was dominant, and during the first part of the 1900s both the insolation changes and the greenhouse
gas forcing are responsible for thermodynamically produced changes. Finally, in the latter part of the 1900s the greenhouse
gas forcing is the dominant factor in determining the sea-ice changes in the Southern Hemisphere.
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| Keywords: | Sea ice Little Ice Age Radiative forcing Wind-Stress forcing Temperature |
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