The Muddling of Climate Models

A news release from the Earth Institute at Columbia University points out that climate models are in no sense "complete" and definitive. Scientists are still grappling with what elements to include in their models. For me, this raises the question of how seriously you can build policy -- especially economic policy -- on a foundation that isn't complete and is subject to significant revision. I'm not opposed to prudential measures, but I am opposed to fanatics who want to stop economic growth and roll back current technologies. I'm leery of models that do linear projections from current trends. I don't see any IPCC models that consider the near term changes to society's dependence on carbon-based technologies.

Here's an example of something new that climate modelers have discovered and now realize needs to be included in their models. I have bolded the key statement:

A new study led by Columbia University researchers has found that the closing of the ozone hole, which is projected to occur sometime in the second half of the 21st century, may significantly affect climate change in the Southern Hemisphere, and therefore, the global climate. The study appears in the June 13th issue of Science. ...

The team of 10 scientists compared results from two sets of climate models, the first one used by the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), released in late 2007, and the second from the Scientific Assessment of Ozone Depletion, published by the World Meteorological Organization in 2006. In their prediction of future climate, many IPCC models did not consider the expected ozone recovery and its potential impacts on climate change. The chemistry-climate models used for the 2006 Ozone Assessment, however, predict that the Antarctic ozone hole will achieve full recovery in the second half of this century, and that this may have profound impacts on the surface winds and, likely, on other aspects of the Earth's climate, including surface temperatures, locations of storm tracks, extent of dry zones, amount of sea ice, and ocean circulation. ...

In the past few decades, the tropospheric winds in the Southern Hemisphere have been accelerating closer to the planet's pole as a result of increasing greenhouse gases and decreasing ozone. This wind change has had a broad range of effects on the Earth's climate. The IPCC models predict that this effect will continue, albeit at a slower pace. In contrast, predictions made by the chemistry-climate models indicate that, as a consequence of ozone recovery—a factor largely ignored by IPCC models—the tropospheric winds in the Southern Hemisphere may actually decelerate in the high latitudes and move toward the equator, potentially reversing the direction of climate change in that hemisphere. ...

While previous studies have shown that ozone hole recovery could lead to a warming of the Antarctic, much work remains. For instance, the chemistry-climate models used in the 2006 Ozone Assessment Report do not include a full ocean circulation, which might affect surface temperatures. The interactions between a recovering ozone hole, increasing greenhouse gases, ocean currents, and other components of the climate system must still be explored in order to better understand how the Earth's climate will change in the future.