One of the most discussed methods of countering global warming is carbon capping and charging carbon dioxide emitters a fee to invest in carbon sequestration technologies. Planting more trees with the money raised is an oft-mentioned solution, the effectiveness of which has yet to be proven.

But how much would that approach cost per ton of carbon dioxide (CO2) emission? What would be its impact on the global economy? The numbers are slowly emerging.

A United Nations report published in May 2007 suggests that the global effort to reduce the emission of greenhouse gases such as carbon dioxide could cost the world economy 3% of its total output by 2030. That is, for 2030 world economic output could be 3%. lower than it otherwise would have been due to the cost of programs to combat carbon pollution.

According to figures from the World Resources Institute, a group of environmental experts in Washington DC, reducing carbon levels to those suggested by the UN report would cost between $20 and $100 per ton of carbon dioxide.

McKinsey & Co., an energy consulting firm, estimates that it would cost $40 per ton of CO2 to reach the 2030 greenhouse gas levels recommended by the UN study.

In Europe, where “carbon trading” has become a new “derivatives trading” specialty, the price of a ton of CO2 is $25, as of May 2007. That’s what it would cost you today have the right to release a ton of CO2 next year.

Duke Energy Corp. of Charlotte, North Carolina, is using the figure of “$7.50 to $30 per ton of CO2” in its future investment plans.

Another learned estimate is provided by Prof. Robert Socolow of Princeton University, quoted by the Wall Street Journal as saying that a carbon cap that would result in a fee of $30 per ton of CO2 emitted would also cost American consumers 30 cents. per gallon at the gas pump.

Thus, estimates still range from $20 to $100 per ton of CO2 released, leaving plenty of room for policymakers and economists to come up with ever-changing alternative plans while providing plenty of reasons for consumers to perplexed they scratch their heads.

The way it looks right now, not just the science and politics, but also the economics of global warming seems equally complex.