Monday, October 11, 2004

Nonlinear Global Warming About To Hit Us?

Most laypeople who acknowledge human-induced global warming implicitely assume that the greenhouse effect is linear: that is, if a given amount of CO2 emissions cause average temperatures to rise by a certain amount, then twice as many emissions will cause a temperature rise also twice as big.

However, in reality, global climate includes a lot of non-linear effects - effects that produce much stronger changes if certain thresholds are passed, and sometimes changes in the opposite direction; effects mostly involving some kind of feedback. Some - even if portrayed as far-off, thanks to great uncertainities about where the thresolds lie - are well-publicised by now: if the Gulf Stream grinds to halt, it alters the global heat transport, cooling the North and heating the South; if ice caps melt, the Earth's heat absorbtion will grow (because there is less ice to reflect most incoming solar radiation away), and the freshwater will probably stop the Gulf Stream; if temperatures rise in artic seas above continental shelfs above a certain temperature, methane trapped in the mud could be released and act as a much stronger greenhouse gas.

Other nonlinear effects are less well known. One is that the accumulation of CO2 in the atmosphere itself depends not only on how much we emit, but also on how much the rest of Nature absorbs from the atmosphere. Most of the latter is not done by trees: both seas and soil are more important - and both absorb CO2 in a way that is not well known, but well enough to say it is temperature-dependent in a non-linear way. Also, peat bogs store a lot of carbon, which can be released as CO2 or methane, also dependent on temperature rises.

Earlier, I have only read studies that told of warning signs regarding peat bogs, but a first sign that there could be something wrong overall was reported today. From the Independent:

...The possibility that it may be occurring now is suggested in the long run of atmospheric CO2 measurements that have been made since 1958 at the observatory on the top of Mauna Loa, an 11,000ft volcano in Hawaii, by the American physicist Charles Keeling, from the University of California at San Diego.

...Across all 46 years of Dr Keeling's measurements, the average annual CO2 rise has been 1.3ppm, although in recent decades it has gone up to about 1.6ppm.

There have been several peaks, all associated with El Niño, the disruption of the atmosphere-ocean system in the tropical Pacific Ocean that causes changes to global weather patterns. In 1988, for example, the annual increase was 2.45ppm; in 1998, 2.74ppm; both were El Niño years.

Throughout the series those peaks have been followed by troughs, and there has been no annual increase in CO2 above 2ppm that has been sustained for more than a year. Until now.

From 2001 to 2002, the increase was 2.08ppm (from 371.02 to 373.10); and from 2002 to 2003 the increase was 2.54ppm (from 373.10 to 375.64). Neither of these were El Niño years, and there has been no sudden leap in emissions.

While the jury is out about the underlying mechanism; Dr. Keeling speculates:

..."It is possible this is merely a reflection of the Southern Oscillation, like previous peaks in the rate, but it is possible it is the beginning of a natural process unprecedented in records.

"This could be a decoupling of the Southern Oscillation from El Niño events, which itself could be caused by increased CO2 in the atmosphere; or it could be a weakening of the earth's carbon sinks. It is a cause for concern."

Of course, politicians and most voters are sleeping. In Europe and Asia. In the USA, they are hallucinating. And they tell us terror is the greatest danger facing our world...


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