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Science Now – Fall 1999

Yes, I realize this is an old article.  I am posting it here not because it is news but because it is well written regarding climate models.  We need good climate models in order to predict the future of our planet and the weather that surrounds it.  Take a minute to read the below excerpts and then jump to the article and read the rest.  It is worth your time if you are interested in this subject.

The first part of the article discusses how climate models work.  This is especially worth your time.

If carbon dioxide continues to accumulate in the atmosphere at its current rate for another hundred years, the sunny Southwest may become soggy and the U.S. Great Plains may be a lot lusher. A new computer projection of the climate of the next hundred years shows an increase in wintertime precipitation in these areas of as much as 40% and a global temperature increase of about 2C (3F) by 2100. If humans manage to cut the buildup of carbon dioxide in half over the next century, rain and snowfall in those areas will remain about the same as now, but the global temperature will still rise some 1.5C. In either case, the sea level will rise 46 to 58 centimeters (17 to 22 inches).

These predictions come from the climate system model (CSM) at the National Center for Atmospheric Research. Scientists at NCAR produced a series of computer runs with the CSM, a global model that includes interacting components for the earth’s atmosphere, oceans, land, and sea ice.

Global climate models represent the earth’s atmosphere as a grid that covers the surface of the globe and extends upward in layers throughout the entire atmosphere. When the model is running, each corner of every square in this grid is like a tiny weather station where the model calculates atmospheric processes. Models come in coarse and fine resolutions, like coarse and fine screens, depending on how much detail is needed. The finer the grid, the more detailed the resulting simulation, but also the more computing time the model requires. A typical global atmospheric model might have ten vertical layers and 65,000 grid points, making a total of more than half a million points.

The researchers found that, despite this difference, global temperature increased and precipitation patterns changed at about the same rate in the policy-limited case as in the business-as-usual scenario until around 2060. The half-century gap before the policies’ effects appear is the result of “thermal inertia.” In other words, it takes that long for the earth–especially the oceans–to heat up or cool down noticeably.

After 2060, the effects of climate change on precipitation in the two scenarios differed considerably (see figure). The difference in global temperature increase between the two scenarios by the end of the century was only half a degree Celsius, but in some regions the effects were more marked. For example, the model showed Europe’s temperature as increasing 50% more under business as usual than under the policy-limited case.

Even with the years of effort that Kiehl, Wigley, and their colleagues have spent on creating a realistic model, collecting the best available data, and developing plausible future scenarios, they are well aware that we cannot know with certainty what 2099’s climate will be. But we do know that climate change is already under way, and future changes are likely to be much greater than any other climate change since the end of the last Ice Age, in both their magnitude and the speed at which they take place. Model results like these help us realize that our own behavior may make the difference between a sunny day and a torrential downpour–if not for our children, then certainly for our great-grandchildren.

Learn more about this article here.

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