1. Modelling Holocene Climate Variability & the Green Sahara
Prof. Alan M. Haywood
School of Earth & Environment, University of Leeds, Leeds, LS2 9JT.

2. Example 1. Mid Holocene 6,000 years ago

3. Example 1. Mid Holocene 6,000 years ago

4. Palaeoclimate Intercomparison Project (PMIP)
Aim was to evaluate whether atmosphere only GCM’s could simulate the mid-Holocene (6000 years BP)
Also, to see what aspects of the model simulations were robust, and which depended on model details.
17 different climate models performed the same simulation (changing orbital parameters only). Models differ in their spatial resolution and their parameterisations of small scale processes

5. The African Monsoon
PMIP Atmospheric GCM’s forced by changes in solar insolation only.

6. N. African Climates: Failure of the GCM’s

7. Why do the models fail? Missing ocean feedbacks?
Missing vegetation feedbacks?
Hewitt ….1998, Brostrom …1998

8. Multiple Equilibrium
Coupled Vegetation-Atmosphere model initialised with different vegetation patterns (Claussen 1994)

9. Multiple Equilibrium
Initialised with “green” Sahara

10. Multiple Equilibrium
Final State

11. Renssen et al. 2006