a simple land cover change intercomparison
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A [simple] land cover change intercomparison. A. Pitman, R. Betts, R. Pielke Sr. et al. Background. LCC affects ~45% of the terrestrial surface (Vitousek et al., 1997) likely an underestimate (Williams, 2003) Globally distributed but regionally centred. Background.

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a simple land cover change intercomparison

A [simple] land cover change intercomparison

A. Pitman, R. Betts, R. Pielke Sr. et al.

background
Background
  • LCC affects ~45% of the terrestrial surface (Vitousek et al., 1997)
  • likely an underestimate (Williams, 2003)
  • Globally distributed but regionally centred
background1
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
status
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.
status1
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.
proposal
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.
proposal1
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
proposal2
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.
proposal3
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
proposal4
Proposal
  • use appropriate statistics to determine whether there are regional impacts of LCC
    • Again, advice encouraged.
timeline
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
objectives
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 !
questions
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 ?
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