Friday, August 4, 2006

The Science of Global Warming: An Obvious Positive Feedback Loop

ScienceNOW News reported today [Science report] on a study by Erickson published in Geophysical Letters that documents one of the more obvious positive feedback loops in the climate system: as global warming creates more heat waves, more CO2 will be produced to provide electricity for our air conditioners.  Erickson combined data from regional climate modelling with regional energy use modelling to assess the impact of warming temperatures on heating and air conditioning.  The  bad news is that winters will not warm enough to reduce CO2 produced from heating:

Think twice before you crank up that air conditioner--you just may be contributing to the heat. The fossil fuels that are burned to power our air conditioners fill the skies with the greenhouse gas carbon dioxide, leading to a warmer world--but the warming won't be enough to lessen heating needs in winter, according to a new climate model. The model is the first to show directly how climate change drives energy use, and the findings could make it easier for policymakers to qualitatively link energy policies to climate change.

Climate researchers typically model Earth on huge supercomputers. A standard experiment might look at the planet between the years 1800 and 2100, tweaking the carbon dioxide levels, sunlight, or cloud cover to understand precisely how these variables affect global and local temperatures. These climate models can suggest what would happen if there were slightly less carbon dioxide in the air, or if there were significantly more snowfall in the Arctic, but they have no way to link economic factors such as increased electricity use to climate change: a 2 degree rise in summer temperatures, for example.

             In the August issue of Geophysical Research Letters, David Erickson, a geophysicist at Oak Ridge National Laboratory in Tennessee, and colleagues in geophysics and economics make the connection. The team took temperature predictions for the years 2000 to 2025 from a standard climate model and plugged them into the National Energy Modeling System (NEMS) developed by the Department of Energy. The program calculates energy consumption due to heating and air conditioning by dividing the United States up by county and taking into account local climate, typical building styles, and the fuel sources for electricity and heat used in each locale. Part of the result was predictable: Carbon dioxide emissions will rise as more coal is burned when the southern and western United States crank up the air conditioning during their ever warmer summers. But the rest was surprising: The northeast didn't necessarily have warmer winters and, furthermore, tended to use heating oil or natural gas instead of coal-fired electricity for heat. The net result was a rise in carbon dioxide emissions over the 25 years.

The combination of regional climate modeling with state of the art economic modeling "makes this study the first of its kind," says Tom Wilbanks, a researcher at Oak Ridge National Laboratory and chair of the National Academy of Sciences' Committee on the Human Dimension of Global Climate Change, who was not involved in the study. The team says the next step is to feed the carbon dioxide trend back into the economic model to see whether ever warmer temperatures lead to ever more air conditioner use.

Climate Change, Energy, North America, Physical Science, Sustainability, US | Permalink

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