Anthropogenic Climate Change ACC

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Anthropogenic Climate Change (ACC)
Adapted slightly from presentation by H. LeTreut
to JSC
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Recommendation of JSC-28 concerning ACC

• A better capacity of WCRP to assert its role in
  and influence on the IPCC assessments, and
  contribute to the SBSTA expertise
• A more effective identification of the scientific
  priorities related to ACC issues, with a
  corresponding strategy and capability to address
  them within WCRP. The Learning from IPCC AR4
  Workshop was noted as an essential part of this
  identification process
• A better definition of the interface with the
  other ESSP components concerning these ACC
  priorities.
• Set-up of an ad-hoc group H. Le Treut, J.
  Church, G. Flato D. Griggs, V. Ramaswamy, A.
  Henderson-Sellers (ex officio),

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Actions during the past year

• The GCOS- WCRP-IGBP workshop Learning from the
  IPCC AR4 (October 2007)
• Links with UNFCCC / Nairobi Work Programme /
  SBSTA. Strong emphasis on the delivery of
  relevant scientific information at the local or
  regional level.
• - ESSP meeting at the past Bonn UNFCCC/SBSTA
  meeting
• - workshop at SBSTA-28 in June 2008 (Climate
  Scenarios, Modelling and Downscaling)
• Links with IPCC (participation in the Aspen
  meeting on the Strategy for Climate Change
  Experiments, and the Amsterdam meeting of the
  definition of scenarios)

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The role of the WCRP Support Group in Paris

• 1 permanent person (Catherine Michaut)
  scientists (H. Le Treut, J. Jouzel, P. Braconnot,
  J.L. Dufresne, S. Planton)
• Main role - help the core projects and the
  working groups in dealing with ACC issues. Two
  main aspects
• Organization of dedicated workshops
• Transmission of information (Web, leaflets, )
• Starting up phase in 2007-2008
• Initial meeting in Paris
• Teleconferences
• Proposal for an initial workshop

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ACC Activities (Draft GF 20/June/07)

• Quantitative projections of climate change, 21st
  century and beyond
• Organize/facilitate international multi-model
  ensemble
• WGCM core activity
• Anything we need to do to facilitate access to
  model output?
• Key improvements in climate models
• Clouds and aerosols (ACC ACPN GEWEX )
• Carbon cycle feedbacks (WGCM/AIMES collaboration)
• Metrics
• Forcing scenarios
• must balance science needs with impacts/policy
  needs
• Netherlands meeting (IPCC WG-3) WGCM contact
  point
• Serving the Impacts community
• Regional Downscaling (what can be done now
  comparing methods facilitating new research )
  WGCM? New group?
• Decadal Prediction (ocean initialization and
  other research areas WGCM, WGSIP, WGOMD, CliVar)
• High Impact or Emerging Issues
• Ice Sheets (mass balance acceleration of ice
  streams) CliC and PAGES?
• Extreme events CliVar
• Air quality coupled to climate change who does
  this?

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• Regional Downscaling in the WCRP
• ACC group has identified regional downscaling as
  a topic in which WCRP should be more active and
  visible.
• The issue
• As identified earlier, many users and
  decision-makers require climate change
  information (from seasons to decades to
  centuries) at spatial scales that reflect local
  and regional conditions. Global models typically
  do not provide this directly.

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• There are several approaches that can be taken to
  downscale from global to regional scale (as we
  know, climate predictions and projections must be
  done at global scale, because the systems
  response is fundamentally global).
• using a regional climate model (RCM) often
  referred to as dynamical downscaling. Note that
  this involves a two-step process, driving RCM at
  its boundaries by results from a GCM.
• making use of empirical relationships between
  large and smaller scales based on historical
  observations referred to as statistical
  downscaling. Note that this requires long-term
  and high-quality observations at the
  location/region in question.
• using a stretched grid global model, with high
  resolution over the domain of interest and lower
  resolution elsewhere. Note that this poses
  challenges for physical parameterizations, flow
  distortion, etc., but avoids problems at
  boundaries.
• use global climate model to produce high
  resolution time slices. Note that this avoids
  boundary problems, but there may be issues with
  initial conditions, parameterizations, ocean
  boundary conditions, etc.

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• Downscaling is dealt with to some extent in
  various parts of WCRP, particularly in WGCM and
  WGNE, but there is not a strong focus, and has
  mainly dealt with RCMs.
• Topic is not visible on WCRP web site or other
  material.
• Sydney Workshop and others have identified
  regional climate change information as a large
  and growing demand by various users.
• Not much guidance available on pros/cons of
  different methods not much quantification of
  relative merits or added value applicability
  at shorter time scales (seasonal to decadal).
• There remain many scientific questions related to
  all of these methods (and there may be merit in
  combing, e.g., dynamical and statistical
  downscaling techniques).

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• JSC agreed to establish a task group under WGCM
  and WGNE to
• Develop a synthesis document summarizing and
  updating existing information about different
  regional downscaling methods, their scientific
  basis, shortcomings, difficulties, etc., to serve
  as guidance for the climate change impacts
  assessment community. This would serve to
  disseminate the knowledge already amassed by the
  regional downscaling community and insure that
  full advantage is taken of this knowledge.
• Develop a longer-term vision for WCRP activities
  in regional climate downscaling, or more
  generally, in methods of providing regional-scale
  climate change information. (following on from
  upcoming Modelling Summit).
• iii. Establish a framework for the evaluation and
  intercomparison of regional downscaling methods
  (along the lines of AMIP and CMIP) to foster more
  critical analysis of these methods and more
  quantitative documentation of the uncertainties
  involved. This would be an ongoing activity aimed
  at promoting research and at informing users of
  regional climate information. The goal here would
  be to raise the profile of such activities and
  thereby make results more widely known.
• RCM workshop in Toulouse in February could be
  kick-off