WASHINGTON, DC - In my last dispatch in this space three weeks ago I complained about the nuisance of the two inches of snow that had come down overnight. Today, after two feet of snow in the last 48 hours, I lay aside my snow shovel to resume worrying about global warming.

The Economist, which provides the best environmental reporting of any major news source, carried a small story last week about a simple methodological error in the latest U.N. global warming report that has huge implications. The article, "Hot Potato: The Intergovernmental Panel on Climate Change (IPCC) Had Better Check Its Calculations" (February 15 print edition), reviews the work of two Australian statisticians who note an anomaly in the way the IPCC estimated world carbon dioxide emissions for the 21st century.

The IPCC's 2001 report, you may recall, produced a wide range of possible emissions estimates, and got headlines for suggesting that world temperature could rise "by as much as" 5.8 degrees. The media, naturally, focused on the worst case, ignoring the hedging and backfilling that qualified the report's projections.

CO2 emissions are a function of energy use, and energy use is a function of economic growth and living standards. Therefore, the IPCC quite reasonably based its emissions estimates on assumptions about future economic growth and improving living standards around the world. Here's where the trouble starts.

Ian Castles of Australia's National Centre for Development Studies and David Henderson, former chief economist for the OECD, note that the IPCC overstates the gap between rich and poor nations today because it converts economic differences according to market exchange rates for currency. A better way to have compared economies is with purchasing power parity (PPP), since market exchange rates don't adequately capture the lower real prices in poorer nations.

The IPCC's method has the effect of vastly overestimating future economic growth (and, therefore, CO2 emissions) by developing nations. The fine print of the IPCC's projections, for example, calls for the real per-capita incomes of Argentina, South Africa, Algeria, Turkey, and even North Korea to surpass real per-capita income in the United States by the end of the century. Algeria? North Korea? The IPCC must be inhaling its own emissions to believe this.

The Castles-Henderson critique means that the IPCC's CO2 emissions projections are implausibly high and need to be rethought. Castles and Henderson note that the emissions record of the period 1990-2000, a period of rapid economic growth all over the world, did not unfold according to the trajectory of the IPCC's model, which adds credence to their criticisms. Castles notes that the economic methodology of the IPCC report has been rejected by the UN's own Statistical Commission.

Castles concludes his letter to the chairman of the IPCC: "I believe that it is important that governments be advised as soon as possible that the economic projections used in the IPCC emissions scenarios are technically unsound."

Now back to my snow shovel.

Steven Hayward is a senior fellow at the Pacific Research Institute in San Francisco and the author of The Age of Reagan--The Fall of the Old Liberal Order, 1964-1980. He can be reached via email at shayward@pacificresearch.org.