In his article entitled "More talk of a warming world in San Francisco," (News-Miner Sundays section, Dec. 28), columnist Ned Rozell reported that Pusker Kharecha of the Columbia University Earth Institute spoke at a press conference on "one of the greatest dangers of a dwindling oil supply - the use of more coal, which releases more greenhouse gases per unit than any other fossil fuel."

"He and his colleagues, including climate scientist Jim Hansen, recommended three immediate solutions to get carbon dioxide emissions in our atmosphere down to 350 parts per million by the end of the century (CO2 currently makes up about 380 ppm of our atmosphere): Coal emissions should be zeroed out by 2030, we should begin reforestation and halt deforestation and we need a tax on carbon emissions," Rozell reported.

Hansen, Kharecha and their colleagues also made these recommendations in an April 2008 article entitled "Target Atmospheric CO2: Where Should Humanity Aim?" in the Open Atmospheric Science Journal (http://aps.arxiv.org/abs/0804.1126).

These three recommended solutions for a decrease of the atmospheric carbon dioxide concentration to a level of 350 ppm by volume are politically motivated.

Even the Intergovernmental Panel on Climate Change does not claim such a decrease in the atmospheric carbon dioxide concentration is feasible. IPCC scenarios that assume a reduction of anthropogenic (human-caused) carbon dioxide emissions during the 21st century to pre-1990 levels show that the atmospheric CO2 concentration still will tend to a so-called equilibrium concentration of about 550 ppmV (see slide 39 of my presentation to the Arctic Climate Impact Assessment Commission in April 2007, available on line at http://housemajority.org/coms/cli/uaf_gerhard_kramm.pdf). Here, equilibrium means that the total (natural plus anthropogenic) carbon dioxide emission equals the total carbon dioxide uptake by vegetation and oceans.

In July, two colleagues and I presented a paper entitled "On the recognition of fundamental physical principles in recent atmospheric-environmental studies," in which a global budget equation for long-lived atmospheric trace gases like carbon dioxide was offered (http://aps.arxiv.org/abs/0711.1551). From this equation, we can infer that the three actions Hansen and colleagues recommended to reduce the atmospheric CO2 concentration are scientifically unsound.

No one knows how much anthropogenic carbon dioxide emissions must be reduced in order to reduce the atmospheric carbon dioxide concentration, because the total uptake also depends on the atmospheric concentration in the immediate vicinity of the earth's surface.

Based on the atmospheric carbon dioxide concentration directly observed at Mauna Loa (Hawaii) and other locations around the world, and the results obtained from Siple (Antarctica) ice core analyses, one may conclude that the total carbon dioxide emission was always higher than total carbon dioxide uptake during the last 250 years. These Siple ice core results play a prominent role in all IPCC reports and serve to extrapolate Charles Keeling's Mauna Loa data (the Keeling curve) to the first half of the 18th century, i.e., before the industrial era began.

Hansen and colleagues also claimed that the ice core results from Vostok, Antarctica, represent the true atmospheric carbon dioxide concentration for more than 400,000 years. We must not expect that the Vostok ice core results have a higher degree of accuracy than the Siple ice core results. Yet the Siple ice core results may be incorrect, as indicated by the carbon dioxide inventory of German scientist Ernst Beck, in which more than 90,000 accurate chemical analyses of CO2 in air since 1812 are summarized.

It is true that coal produces one-third more carbon dioxide per British Thermal Unit than most petroleum products. Coal is mainly used for electrical power generation and heating. If we replace coal with petroleum products, we will cause oil supplies to dwindle faster. If our goal is to reduce carbon dioxide emissions, the only reasonable action is to substitute coal-generated energy with nuclear energy.

Renewable sources such as wind energy, geothermal energy, hydroelectric power, photovoltaic and solar thermal energy should only be considered supplements. Replacing, for instance, a coal power plant of 100 megawatts would require 300 to 400 wind generators, even if we assume a nominal performance of 2 to 2.5 MW per wind generator. And the problem of storing of wind-generated energy during long-lasting periods of calm has not been solved.

Is such a substitution reasonable for Interior Alaska? Certainly not. During winter, calm often comes with ambient temperatures far below the freezing point. During such weather conditions, it is indispensable to use fossil (or nuclear) fuel for generating electrical power and heating. So coal (or nuclear) power plants would have to be maintained continuously, even if a huge wind farm has been established.

Gerhard Kramm, Ph.D., is an atmospheric scientist with the Geophysical Institute at the University of Alaska Fairbanks.