Background/Question/Methods

Our knowledge of the links between greenhouse gasses and planetary warming is almost entirely based on historical data and simulations. Not only are we not able to create functioning analogues of the Biosphere under experimental conditions, but in most attempts to estimate and model carbon pools and fluxes at a global scale we find it extremely difficult to deal with potential feedbacks. We have created small scale analogue models of the terrestrial carbon (C) cycle using the same ratio of carbon in the main pools present in our system (soil, vegetation and air) as the global ones estimated by the IPCC 2001. Just as in the Earth, our 100 litre replicated model systems are materially closed but energetically open. Each was set up with an initial atmospheric CO₂ concentration at the pre-industrial level of about 280ppm and with the temperature maintained at 15^oC. Aiming to test the strength of the CO₂-Temperature (T) feedback three treatments were applied: 1) isothermal 15^oC, simulating the global average temperature, 2) isothermal 18^oC, representing the average temperature predicted for the end of this century and 3) 18^oC plus a dynamic feedback linking the temperature to any CO₂ concentration increases. We have used mid-range forecast predicting an increase of 3^oC when atmospheric CO₂ concentration doubles. The hypothesis under test is that introducing such feedback will result in steadily increasing and runaway atmospheric CO₂ concentration.

Results/Conclusions

We have observed an increase in the CO₂ in the isothermal 18^oC (347ppm) and 18^oC plus feedback (354ppm) treatments compared with the isothermal 15^oC (320ppm). However, contrary to scenarios predicting a runaway warming due to CO₂-Temperature feedback, there was no difference in the CO₂ concentration between the 18^oC and 18^oC plus feedback treatments. Our preliminary observations suggest that the predicted link between doubling of CO₂ concentration and average global temperature increase by 3^oC does not constitute a feedback mechanism strong enough to lead to a CO₂ runaway warming scenario.