Polar Climate Predictability Initiative - Understanding Changes and Improving Predictions

1. Report to PPP SC meeting, Reading, 12 December 2012 WCRP Polar Climate Predictability Initiative (PCPI) Ted Shepherd Department of Meteorology University of Reading

2. Scientific Context • Important and puzzling changes are occurring at the poles • Record Arctic sea-ice minimum in Sept 2012 • Record Antarctic sea-ice maximum in Sept 2012 • Agreement between models and observations is not particularly good in polar regions • Polar regions appear to be important for global climate, not just “canaries in coal mines” (e.g. role of Southern Ocean) • Polar regions may contain sources of predictability on both seasonal and decadal time scales (subpolar seas, snow cover, sea-ice extent, stratosphere…) • Forced component of predictability may be strong on decadal timescale, especially in the Arctic

3. Programmatic Context • Polar climate predictability cuts across all elements of WCRP; but tends to fall between the cracks • WCRP Working Groups need process expertise in polar regions to help improve products and strategies • WMO Global Producing Centres for Long-range Forecasts • Global Framework for Climate Services • WMO EC-PORS is promoting a Global Integrated Polar Prediction System (GIPPS) • WWRP Polar Prediction Project: hours to seasonal • WCRP PCPI: seasonal to multi-decadal • Will liaise closely, have a common coordination office

4. Programmatic Context, continued • There are existing international programs specifically focused on the polar regions: IASC for the Arctic, and SCAR for the Antarctic • Need to avoid duplication or competition (or confusion) • WCRP brings the global perspective and strength in global modelling • Within WCRP, the PCPI will constitute a sub-initiative of the “Cryosphere in a Changing Climate” Grand Challenge • The PCPI can be an ‘incubator’ to generate community research efforts that could be adopted, in the longer term, by more permanent components of the WCRP or of partner organizations

5. Key Scientific Questions • How predictable is Arctic climate? • Why are the climates at the two poles changing so differently to each other (with the Arctic changing rapidly, and the Antarctic unevenly), and differently to global climate? • Why are climate models generally unable to capture the observed behaviour in polar regions? • What does high latitude climate change mean for lower latitudes? • Do the ongoing amplified changes in the Arctic have an influence on extremes in the Arctic? • Is the stability of ice sheets changing?

6. Opportunities for Significant Progress • Recent expansion of the ocean observing system • New measurements of sea-ice thickness and other important surface variables • New reanalysis products • More comprehensive global models • The pieces are in place • Much progress can be achieved just by bringing together previously disparate scientific communities to work on common problems that involve a strong coupling between the different components of the climate system • Interest of the scientific community • Synergy with the WWRP-PPP

7. Specific Initiatives (not prioritised) • Improve knowledge and understanding of past polar climate variations (100+ years) • Assess reanalyses in polar regions • Improve understanding of polar climate predictability on seasonal to decadal timescales • Assess performance of CMIP5 models in polar regions • Develop methods to calibrate long-term predictions of polar climate change • Improve understanding of how jets and non-zonal circulation couple to the rest of the system in the Southern Hemisphere

8. Status • Planning meeting was held in Toronto (April 2012), joint with IASC-Atmosphere (~30 participants) • Built strongly from the much larger Bergen workshop in October 2010 (report published in SPARC Newsletter) • Led to a crowd-sourced implementation strategy • Subsequently polished and broadly circulated; finalized in early November 2012, and provided to JSC • Now need to move ahead with specific, targeted activities ranging from focused workshops to coordinated efforts of up to 2-3 years’ duration • The WCRP Workshop on Climatic effects of Ozone Depletion in the SH (Buenos Aires, Feb 25–Mar 1) can be part of this

9. Status, continued • Grand Challenges are being carried forward by the Core Projects as a supplement to their core activities • There will be a separate WCRP budget line for GC workshops • PCPI is under the overall leadership of CliC (since part of the Cryosphere GC), but SPARC will lead the PCPI • Secretariat support available from SPARC IPO (Dr. Diane Pendlebury, funded by the Canadian Space Agency)

10. Potential connections with PPP Also via WGNE, GASS, WGSIP

11. Thoughts on connections with PPP • Improved observations of ocean, snow cover, and sea ice are certainly of common interest • Model errors in polar regions are of great interest to PCPI — e.g. stable boundary layers — but the spatial resolutions of the models are rather different • PCPI should try to foster increased use of short-term predictions to identify errors in climate models, through WGNE — but only works if initial condition is reasonable • Synergy on data assimilation is limited as the real assimilation mainly takes place in NWP centres anyway • Mechanisms of predictability at seasonal timescales is an obvious common interest (e.g. stratosphere)