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

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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


Chase et al 2000

Chase et al, 2000


Betts 2000

Betts, 2000


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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