TCS Daily

Scratching Your Head Over Climate Change

By Robert C. Balling - April 5, 2005 12:00 AM

No day goes by without another story regarding global warming, and the latest news has scientists throughout the world scratching their heads about climate change. A team of scientists reports in the prestigious journal Science that dandruff levels in the atmosphere are surprisingly high, and the load of biological aerosols from flaking skin, fur, and pollen can make up between 25% and 80% of the aerosols in the atmosphere. These aerosols are important building blocks for clouds, and clouds remain the greatest mystery in the global warming debate. If our future has more high clouds, any greenhouse warming will be amplified, but if our future has more low clouds, their ability to reflect away solar radiation will dampen any warming caused by elevated concentrations of greenhouse gases. Clouds are widely recognized to be the wild cards in the greenhouse debate, and at present, clouds are notoriously poorly represented in numerical models of climate. The latest news about dandruff has implications for future clouds, and the results from the German team mean more uncertainty in predicting the future climate.

In 1990, concern over global warming prompted the United Nations to publish its first major scientific assessment by the Intergovernmental Panel on Climate Change (IPCC). Almost all of that assessment dealt with the climate impact of elevated atmospheric concentrations of carbon dioxide and other greenhouse gases. Only two years later, the IPCC released an amended report that included the effects of sulfate aerosols, which come from fossil fuel burning, and once in the atmosphere, reflect sunlight, brighten clouds, and make clouds last longer. Sulfates have a cooling effect that must be considered in predicting future temperatures of the Earth. By 1995, the IPCC scientific assessment was expanded to include the global and regional climatic effects of various greenhouse gases, stratospheric ozone, tropospheric ozone, sulfate aerosols, fossil fuel soot, biomass burning, mineral aerosols, and variations in solar output. The IPCC scientists added black carbon, organic carbon, jet contrails, and land-use changes to the list in 2000. This all lead Dr. James Hansen, a prominent greenhouse scientist with NASA's Goddard Institute for Space Studies, to write in the Proceedings of the National Academy of Sciences "The forcings that drive long-term climate change are not known with an accuracy sufficient to define future climate changes."

The global warming scientific debate at times seems to be a squabble regarding how quickly the Earth is warming (or if it is warming at all), where the warming is occurring, the time of year of any warming, whether the warming is good or bad, or most importantly, whether policy actions would have any impact on the warming. The latest report from the German scientists about dandruff, fur, and pollen is a reminder that our knowledge of controls on the climate system is far from complete, and as we see in the IPCC reports, new "forcings" of climate are added in each major assessment. Even if we had perfect temperature records of the Earth and numerical models that accurately simulated the climate system, we do not know enough about how the various "forcings" will impact the climate system over the next 50 to 100 years.

We are all itching to know what will happen to the climate system over the next century, and year after year, scientists make discoveries that further complicate predicting climate into the future. And while the climatologists grapple with atmospheric questions, others are left to determine how many people will be on the Earth in the future, if developing economies develop or remain stagnant, if there will be breakthroughs in energy generation, and on and on. Uncertainties in these arenas are as great or greater than uncertainties in climate models, temperature records, or the factors that will change the climate system over the coming decades.

We cannot wash away these uncertainties in any discussion of policy actions, and as we see in the latest news about dandruff, important changes to the atmosphere may be undiscovered at this time. Anyone claiming to know where we are headed climatically, with or without policy actions, is disregarding the complexities in predicting the future climate of the Earth.

Dr. Robert C. Balling, Jr. is with the Department of Geography, Arizona State University


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