It's back to carbon dioxide -- that indispensable (for all life an earth) molecule which EPA keeps trying to classify as a pollutant so they can regulate it. The latest dispute deals with the recently discovered North American carbon sink, which may be larger than the carbon source from fossil-fuel burning. If proven true, then the US is already ahead of the Kyoto Protocol. Al Gore, take note!

CARBON SINK HITS FAN to borrow the catchy headline by David Wojick in the Electricity Daily A major scientific fight has developed over the existence, magnitude and permanence of the great North American carbon sink, published last October by Princeton scientist S.M. Fan and colleagues. Their expectation was that carbon dioxide would increase over North America as the winds moved from west to east, due to the large amounts of carbon dioxide produced by fossil-fuel burning. Instead, data from 63 atmospheric sampling stations showed carbon dioxide declining slightly during the period of the study (late 1980's). In Technical Comments to Science, two research groups have attacked Fan's "inverse estimate method" results.

The first group, led by Elisabeth Holland [National Center for Atmospheric Research], complains that Fan's results don't jibe with ecological mechanisms. The second group, headed by Christopher S. Potter [NASA], took a fundamentally different approach. "We used newly derived terrestrial carbon fluxes, predicted directly from forward-modeling in a non equilibrium mode (using observed interannual variability for surface climate and satellite imagery). The Fan group sticks to its guns, however, responding that "The intercomparison between our inverse estimates (based on atmospheric and oceanic data and models) and estimates based on mechanistic models and ground data must take into consideration the large temporal variability of the terrestrial C cycling. The large interannual CO2 variability must have been caused mainly by terrestrial ecosystem productivity and respiration." In plain English, they think the sink is there. But all parties agree that more research is needed to reconcile the discrepancies. A report in Science [April 2] predicts dire consequences for coral reefs, if carbon dioxide continues to increase in the atmosphere. Of course, this is all based on calculations which consider only one set of chemical reactions that would lower the concentration of something called Aragonite, a mineral phase of calcium carbonate. Unfortunately [or perhaps fortunately, we are not sure which], these folks have neglected to take into account that global warming that is supposed to go with higher level of CO2. Doesn't warming drive out CO2 from the ocean layer and lower the concentration? They report that the average tropical concentration of aragonite has decreased over the past century, but we know the temperatures also increased during the first half of the century, presumably lowering the CO2 concentration. Something doesn't jibe here.

Let's remember that without CO2 in the water, the critters [bryzoans and polyps] that make reefs would have no basic building materials to grow. But the anxiety machine is already working full blast. The Australian co-author of the paper gave an interview [reported by AP], which announced the increasing risk facing the Great Barrier Reef, Australia best-loved tourist attraction. He allowed as to how the reef was not in danger of imminent collapse, but warns Australians about the loss of tourist income.

What's causing the bleaching of coral reefs? No one is sure. Some postulate warmer sea surface temperature for "unprecedented coral bleaching" in the Caribbean area; but a University of Miami group could not find a warming. Other causes have been mentioned, such as high UV light-intensity [very popular in Australia], and pathogens, bacteria, parasites. And of course, there are those who blame the pathogen on global warming.

Modelers are always eager to bring up new kinds of feedback that could lead to disasters. For example, rising atmospheric CO2 levels can lead to increased radiative forcing that results in higher sea surface temperatures, that increase evaporation and rainfall, that may reduce ocean salinity at high latitudes In turn, these changes could affect the oceanic circulation driven by temperature and salinity differences, and could cause a collapse of the North Atlantic Deep Water formation, affect carbon marine cycles, and reduce the transport of carbon from the surface to the deep ocean. This could result in a reduced carbon uptake by the ocean and accelerate the growth of CO2 in the atmosphere, completing the cycle. Again, note the myopic view of the modelers, who don't investigate whether a warming in the past history of the Earth might have produced the same cycle.

Good news from the Duke University forest in North Carolina (and great consternation among enviros). Increasing the carbon dioxide level of the air around the trees to what it might be in 2050 boosts growth rate by 25% over the rate for trees in control plots. Publishing in Science (May 14), the authors suggest that this figure may be a maximum value. Still, if all of the world's forests were to increase uptake by 25%, it would take care of half of the world's emission in 2050.

Other good news. The high CO2 plots didn't suffer as much during the drought conditions of 1997-98, confirming that higher CO2 levels also reduce water requirements. And the bad news: Urban sprawl might well impinge on forests. There you have it; seems that every silver lining has a cloud. As the doctor told his patient: "The good news is you're not a hypochondriac …."