Sun, May 13, 2007 - Page 8 News List

Letters: Combating global warming

Noted environmental advocate Jim Hansen, in his testimony before the US House of Representatives this year, said that the "dangerous level of CO2 is at most 450ppm [parts per million], and it is probably less." Hansen added: "Note that I do not specify an exact fraction by which CO2 emissions must be reduced by 2050 or any other date, but we can say that emissions must be reduced to a fraction of their current values."

The current carbon dioxide level in the atmosphere is about 383ppm, having risen 2.6ppm last year. Human carbon dioxide emissions now rise by approximately 3.5 percent per year.

While nature soaks up about half of human carbon dioxide emissions now, that is expected to drop to 30 percent by 2030. In other words, a growing and developing world population has less than 20 years before the carbon dioxide level reaches 450 ppm.

However, using a more accurate measurement of carbon dioxide equivalent will show that the total of all greenhouse gases (GHG) in the air is 459ppm -- meaning, we've already passed the 450ppm mark.

To lower the chance of global warming by half, global GHG emissions must be cut 80 percent by 2050.

As developing nations continue to increase their GHG emissions per capita, it's only fair that they have to cut their emissions by more than 90 percent per capita. In other words, by 2050 Americans will have to cut their GHG emissions by more than 90 percent from this year's levels.

To lower the carbon dioxide level in the atmosphere, we either have to decrease our carbon dioxide emissions dramatically, or find a solution to improve nature's ability to lower carbon dioxide levels in the air.

Since worldwide demand for electricity is expected to double by around 2030 and coal-fired power plants account for about 30 percent of the supply, it is hard to see how carbon dioxide emissions can be reduced in a short time.

These carbon dioxide emission figures do not even include other factors, like increased natural emissions from carbon sinks that become carbon emitters when the earth continues to warm, increased growth of fossil fuel powered transportation, increased agricultural GHG emissions, or even decreased global dimming if emissions decrease.

Nature partially takes carbon dioxide out of the environment with plants that convert it into carbohydrates, and animals that convert it into tissue, bone and shell. Both are examples of autotrophs, which produce their own organic compounds using carbon dioxide from the air or water in which they live.

To do this they require an external source of energy, and almost all autotrophs use solar radiation to provide this.

The GHG can re-enter the atmosphere through decay or combustion. In fact, the carbon dioxide level in the air naturally fluctuates by about 6ppm per year as biomass grows and then shrinks with the seasons.

Because of a bias against releasing genetically engineered organisms into the environment, removing carbon dioxide from the air with naturally evolved autotrophs would be best.

The autotrophs that remove the most carbon dioxide from the environment are trees on land and phytoplankton in the ocean. Yet, neither removes the carbon dioxide for long before they die and release carbon dioxide back into the air through decay.

An expanding human population also places land use for reforestation at a premium, while decaying phytoplankton depletes oxygen in the ocean, leading to dead zones and the production of hydrogen sulfide by bacteria.

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