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 15oC. Aiming to test the strength of the CO2-Temperature (T) feedback three treatments were applied: 1) isothermal 15oC, simulating the global average temperature, 2) isothermal 18oC, representing the average temperature predicted for the end of this century and 3) 18oC plus a dynamic feedback linking the temperature to any CO2 concentration increases. We have used mid-range forecast predicting an increase of 3oC 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 18oC (347ppm) and 18oC plus feedback (354ppm) treatments compared with the isothermal 15oC (320ppm). However, contrary to scenarios predicting a runaway warming due to CO2-Temperature feedback, there was no difference in the CO2 concentration between the 18oC and 18oC plus feedback treatments. Our preliminary observations suggest that the predicted link between doubling of CO2 concentration and average global temperature increase by 3oC does not constitute a feedback mechanism strong enough to lead to a CO2 runaway warming scenario.
