Parkinson, C.
L.,
D. Rind, R. J. Healy, and D. G. Martinson, 2001: The
impact of sea ice concentration accuracies on climate
model simulations with the GISS GCM, J. Climate, 14 (12),
2606-2623.
The Goddard Institute for Space Studies
global climate model (GISS GCM) has been used to examine the sensitivity
of the simulated climate to the percent areal coverage, or concentration”,
of sea ice specified in the polar oceans. Sea ice reflects back toward
space most of the solar radiation that reaches it and furthermore tends to
insulate the ocean from the atmosphere. Hence, the greater the sea ice
cover, the colder the air temperatures are expected to be. The simulation
results show that sea ice concentration uncertainties of 7%, which is
roughly the estimated uncertainty in sea ice concentration retrievals from
current satellite instruments, can affect simulated regional temperatures
by more than 6°C. Furthermore, uniform +7% and -7% changes in ice
concentrations produce changes in the simulated annually averaged global
surface air temperatures of -0.10°C and +0.17°C, respectively. The
resulting 0.27°C difference in simulated annual global surface air
temperatures is reduced by a third, to 0.18°C, when considering instead
biases of +4% and -4%, which is roughly the estimated uncertainty for
satellite retrievals from upcoming satellite instruments.
In a larger suite of sensitivity studies, seventeen simulations were run
with ice concentration input changes ranging from increases of 50% versus
the control simulation to decreases of 50%. Results show, on average, a
0.0107C warming of global surface air temperatures for every 1% ice
concentration decrease. This equates to a 1.07C warming for the full +50%
to 50% range. Regionally and on a monthly average basis, the differences
can be far greater, especially in the polar regions, where wintertime
contrasts between the +50% and 50% cases can exceed 30C. However, few
statistically significant effects are found outside the polar latitudes,
and temperature effects over the non-polar oceans tend to be under 1C.
For comparison, climate models suggest a global surface air temperature
increase of about 2-4C in the event of doubled atmospheric carbon dioxide
(CO2).
