One of the abiding, but extremely potentially foreboding, uncertainties in climate science is possible positive feedback mechanisms associated with climate change. A recent study analyzes one of these mechanisms, potential melting of ocean methane hydrates, David Archer, et al., Ocean Methane Hydrates as a Slow Tipping Point in the Global Carbon Cycle, 106 Proceedings of the National Academy of Sciences 20596-20601 (Dec. 8, 2009) (subscription required).
Among the key take-aways from the study:
- Large amounts of methane are trapped in the sediments beneath sea floors in the form of water ice called methane hydrate; methane is a potent greenhouse gas that oxides in about a decade to carbon dioxide;
- While the hydrate carbon reservoir has most likely accumulated over millions of year, a release of carbon from the hydrate pool would likely take place over a time scale of a millenia;
- A 3C increase in temperature could reduce the steady-state inventory of methane by more than half; this would take place over a period of several thousand years, increasing atmospheric temperatures by 0.4-0.5C. If the methane reaches the atmosphere, it would send temperatures significantly above the 2C benchmark also for thousand of years;
- The temperature spike precipitated by hydrate melting was simulated to continue for the entire 10,000 duration of the simulations in the study;
- The impact of hydrate melting is “to prolong the period of near-peak warming for thousands of years.”
This is another good study to explain the concept of positive feedback mechanisms to students, as well as another example of why decisions that we are making now may have implications for scores of future generations. Stay tuned; another study on this topic is due to be published this Thursday in Science.