A [simple] land cover change intercomparison

1. A [simple] land cover change intercomparison A. Pitman, R. Betts, R. Pielke Sr. et al.

2. Background • LCC affects ~45% of the terrestrial surface (Vitousek et al., 1997) • likely an underestimate (Williams, 2003) • Globally distributed but regionally centred

3. Background • Deforestation experiments demonstrate an impact on regional climates • But some are now attributing large changes in climate remote from LCC to LCC via teleconnections • Mechanisms include Walker and Hadley cell changes and Rossby wave propagation

4. Chase et al, 2000

5. Betts, 2000

6. Status • The IPCC (2001) notes possible regional impact of LCC; • some are interpreting GCM results as evidence of the global scale impact of LCC; • Others see LCC only in terms of radiative impacts • Some see any remote effects of LCC as ‘model variability’. • either might be true - but it is something that we need to know more confidently.

7. Status • There are problems with the design of all attempts to explore the climate impact of LCC using GCMs • Many use short (<20-year) simulations for natural and current vegetation; • Most perform single realizations; • Many perform standard t-tests that do not account for the autocorrelation in the data; • Spatial resolution tends to be quite coarse.

8. Proposal • A LCC intercomparison involving 10-15 groups with: • a common land cover perturbation (historical land cover to current). We might do a future scenario too; • AMIP-2 length simulations, using the AMIP-2 design; • multiple realizations with each model (5-10); • use appropriate statistics to determine whether there are regional impacts of LCC.

9. Proposal • a common land cover perturbation (historical land cover to current, but we might do a future scenario too); • Crops + other [Betts/de Noblet] • 1900 and 2000 snap-shots • Static vegetation • Modellers free to translate changes into pfts • Future scenario not decided

10. Proposal • AMIP-2 length simulations, using the AMIP-2 design; • Fixed SSTs • Limiting relevance but cheap and easy: inclusive • Easy for most groups • AMIP-2 standard output format (easy) • We need to recognise that the set of people who are pushing LCC as a major climate driver have limited overlap with core climate modelling groups … limits the level of experimental complexity that is possible. • It is more politically important to include these groups that have a larger sample of core climate modelling groups.

11. Proposal • multiple realizations with each model (5-10); • Advice from GLASS appreciate on the number required; • Advice welcomed on best way to perturb the sample

12. Proposal • use appropriate statistics to determine whether there are regional impacts of LCC • Again, advice encouraged.

13. Timeline • We wanted to mesh with IPCC [not possible] • Review paper from the community • Data sets available by November/December 2004 • Simulations performed by October 2005 • Analysis over the subsequent six months. • data will be made available to individual groups

14. Objectives • We do not aim to “answer” the LCC question; • We aim to start a process – if the LCC community conduct these experiments and the answers are interesting, we have a common foundation to build from • Our experiments are limiting – but we have to balance what is achievable by the specific community we are trying to involve • If GLASS thinks the experiments are too limiting then we would prefer to know now !

15. Questions • Is this worth doing ? • relatively cheap, but it is limited in scope; • too slow for IPCC 4th assessment • would force some to confront model variability cf. teleconnection issue • Is AMIP-2 ok as a framework ? • Advice on the LCC data ? • Realizations ? • Statistics ?