Worldwide, carbon dioxide (CO2) levels have risen again, according to the National Oceanic and Atmospheric Administration (NOAA).

The rise, a disturbing 2.6 parts per million over 2006 levels, is attributed primarily to the burning of fossil fuels. However, another factor, which may present its own tipping point, is global warming’s effect on forests.

When the earth warms, several things happen to forests. Boreal forests are displaced farther north, and the timberline (the altitude beyond which trees can’t grow) rises. Where warming is precipitous, forests fail to adapt and die, or are ravaged by pests which thrive in the absence of annual freezing. U.S. government reports indicate that temperate forests (maple-beech-birch) will shift north into Canada by the late 21st century.

Forests act as carbon sinks, or storage depots. When trees grow, they store CO2 in a complex process that uses sunlight (photosynthesis) to convert CO2 and water into carbohydrates (food) and oxygen. When trees die, the process is reversed. All plants do this, but trees – with their longer life spans and greater mass – do it on a more significant, and more observable, level.

Forest destruction is now happening all over Canada, as pine beetles destroy more than 50,000 square miles of forest, releasing an estimated 270 megatons of CO2 over the next 14 years. This represents the same amount that would potentially be reduced under the Kyoto Protocol, leaving a net gain to the environment of zero, at least on Canada’s part.

The same infestations are being seen in the U.S. Northeast and Upper Midwest, with equally disastrous effects. In the West, entire stands of trees, weakened by drought (a regional side effect of global warming), have succumbed to pests, leaving the “stick-forests” of nightmares. From Washington to central Oregon, forests are dying from the top as trees turn an appalling shade of rust. In Japan, as recently as 2006, foresters were being encouraged to cull dead trees resulting from global warming (this in a country not known for its vast forests).

In addition to rising CO2, the NOAA reports a substantial rise in methane over the last decade. Methane escapes when Arctic permafrost melts. Although the NOAA admitted it was too soon to tell if the current methane increase signals rapid Arctic thawing, the evidence – flooded Alaskan villages suing energy companies, and images of polar bears stranded on ice floes – speaks for itself. Scientists know that, if the Arctic permafrost thaws, catastrophic amounts of methane will be released, as they were in Western Siberia in 2006.

When methane gets into the atmosphere, it increases the rate of global warming in a vicious cycle known as a “positive feedback loop”. According to Chris Field, the director of global ecology at the Carnegie Institution of Washington, this is an ominous development, because these warming mechanisms tend to be self-perpetuating.

Sergei Kirpotin of Tomsk State University in Western Siberia notes that melting permafrost is an "ecological landslide” which is likely irreversible, and Larry Smith from UCLA estimates that the westernmost portion of the Siberian bog alone contains about 77 billion tons of methane, or one quarter of all the methane stored in landmasses worldwide.

As forests die, releasing CO2, and permafrost melts, delivering methane, the earth – caught in this self-perpetuating loop – reaches a tipping point; a day and time beyond which it is no longer possible to restore the balance. This writer suspects we have already passed that point of no return. The results will be catastrophic climate change, increasing extinction of animal and beneficial insect species, crop failures, mass starvation and death from disease, all because we had to have SUVs and cities so bright they are visible from space.

Further Reading:

• The ‘Dangerous Threshold’ - a Destination, or a Milestone?
• Feedback Loops: Melting Permafrost
• The Eight Most Sobering Reports of 2007
• Melting from Pole to Pole
• Tropics on the Move - Diseases Too
• CO2 Output Must Cease, Entirely. What To Do?