Long-term climate change models
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The international climate community has focused considerable research on
detecting and projecting climate change over the next century. Typical modeling
experiments simulate the transient global warming response of the coupled
atmosphere-ocean system to an expected doubling of the atmosphere's
CO2 content over the next century. However, recent analyses of future
emission scenarios in international climate change assessments suggest that, on a
multi-century time scale, CO2 levels are likely to rise well beyond a
doubling unless substantial emission reductions occur. To address this potential
long-term scenario, NOAA's scientists at the Geophysical Fluid Dynamics
Laboratory (GFDL) have performed a series of multi-century integrations of a
global coupled ocean-atmosphere model in which CO2 increases by one
percent each year to a level four times that of the present climate and then
remains constant thereafter.
Results from these quadrupled CO2 experiments (4xCO2 ) are
compared to a control run with current-day concentrations. The experiments
project a substantial increase in surface air temperature, with the summer
warming predicted to increase markedly over much of the mid-latitude continental
regions, including North America and Asia. The experiments' temperature changes
are nearly as large as the difference between the present climate and that of the
Late Cretaceous Period that occurred approximately 65-90 million years ago when
dinosaurs still inhabited the Earth. While model resolutions are quite low
compared to those used for daily weather forecasts, the five-century duration of
each model run requires many hundred processor-hours to complete on a high
performance computing system.
Along with surface warming, sea ice coverage over the Arctic Ocean is projected
to decrease substantially. Mean sea ice thickness (in meters) in the model during
late winter is shown in the illustration. The view is from above the North Pole;
brown areas indicate the model's land regions. During late summer (not shown),
sea ice is virtually absent in the 4xCO2 experiment.
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