Climate variability-induced uncertainty in mid-Holocene atmosphere-ocean-vegetation feedbacks

Previous modelling studies have shown that the response of the ocean and the vegetation to mid-Holocene insolation feeds back on the climate. There is less consensus, however, on the relative magnitude of the two feedbacks and the strength of the synergy between them. This discrepancy may arise partly from the statistical uncertainty caused by internal climate variability as the common analysis period is only about a century. Therefore, we have performed an ensemble of centennial-scale simulations using the general circulation model ECHAM5/JSBACH-MPIOM. The direct atmospheric response and the weak atmosphere-vegetation feedback are statistically robust. The synergy is always weak and it changes sign between the ensemble members. The simulations, including a dynamic ocean, show a large variability at sea-ice margins. This variability leads to a sampling error which affects the magnitude of the diagnosed feedbacks. Citation: Otto, J., T. Raddatz, and M. Claussen (2009), Climate variability-induced uncertainty in mid-Holocene atmosphere-ocean-vegetation feedbacks, Geophys. Res. Lett., 36, L23710, doi:10.1029/2009GL041457.