29 April 2008

Future trajectories

The tally on last year's emissions are in. The verdict: Guilty as charged! Concentrations of CO2 continue to rise at an increasing rate. Last year, the average value rose by 2.4 ppm in 2007; previous concentrations were rising at 2 ppm/year. There is little sign that this is likely to stop anytime soon, given the nearly-meaningless emissions reduction measures announced by the US. The CO2-enhancement experiment will be carried out to the end.

Perhaps more concerning, methane (CH4) levels also rose for the first time since 1998. Methane is a much more potent greenhouse gas, although it has a much lower concentration in the atmosphere. The recent rise does not necessarily imply an immanent trend, but there is some concern. One expected consequence of increasing temperatures is a melting of the Arctic permafrost and/or the methane clathrates under the sea.

This spike in CH4 could be a sign of this beginning to occur. Paleoclimate studies of historical GHG concentrations using ice cores are suggestive, to wit

The study shows, that tropical wetlands emitted substantially less CH4 during glacials; most likely caused by changes in monsoonal precipitation patterns. Together with a reduced atmospheric lifetime, this explains major parts of the glacial CH4 reduction. In addition, boreal methane sources located in wetlands in higher northern latitudes were essentially switched off during the glacial due to the expansion of the northern ice sheets and the very cold temperatures in high northern latitude. However, these high latitude wetlands were quickly reactivated when rapid climate warming events occurred. Also forest fires emit a considerable amount of CH4, which, however, remained surprisingly constant over time. The isotopic measurements show no signs of CH4 emissions by a destabilization of marine gas hydrate reservoirs when climate was warming.

Measurements of the sea floor north of Russia are indicating that the clathrates here are destabilizing.

The permafrost has grown porous, says Shakhova, and already the shelf sea has become "a source of methane passing into the atmosphere." The Russian scientists have estimated what might happen when this Siberian permafrost-seal thaws completely and all the stored gas escapes. They believe the methane content of the planet's atmosphere would increase twelvefold.

If this becomes permanent reality, expect the impacts of climate change to rapidly accelerate. Combined with ever-increasing CO2, this would provide a staggering blow to our society. Such a rapid climate change would render the option of mitigation moot, leaving only the less-appealing tactic of adaptation available.

As noted in this excellent op-ed piece, the relatively small warming we have experienced to date has “...already taken the planet into a condition where human experience no longer provides a reliable indication of the future”. Given the difficulty of society to cope with the global crises we are currently experiencing (only in part due to climate...), it's hard to see how this situation will improve in a more extreme future.

Sadly for our children, it seems unlikely that appropriate measures will taken to mitigate the approaching calamity. It's quite possible that it is too late in any case. This ever-upward carbon trajectory likely means that humanity's future trajectory is downward.

Images: NOAA, via The Great Beyond

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