1 / 21

A few questions about climate models

A few questions about climate models. A paradox: The patterns of global climate change predicted 30 years ago and confirmed since then Continuous progress in weather forecast, oceanic forecast A lasting difficulty to quantify potential effects of climate change, and their regional properties.

aitana
Download Presentation

A few questions about climate models

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. A few questions about climate models A paradox: • The patterns of global climate change predicted 30 years ago and confirmed since then • Continuous progress in weather forecast, oceanic forecast • A lasting difficulty to quantify potential effects of climate change, and their regional properties.

  2. Pourquoi la modélisation climatiqueest-elle possible? • Henri Atlan : «Il y a un problème de crédibilité des modèles de changements climatiques et des prédictions qui en sont déduites. Ces modèles concernent en effet un domaine - le climat - où le nombre de données disponibles est petit par rapport au nombre de variables qui sont prises en compte dans leur construction, sans parler des variables encore inconnues. Cela implique qu'il existe un grand nombre de bons modèles, capables de rendre compte des observations disponibles, alors même qu'ils reposent sur des hypothèses explicatives différentes et conduisent aussi à des prédictions différentes, voire opposées. Il s'agit là d'une situation dite "des modèles par les observations", cas particulier de "sous-détermination des théories par les faits", bien connue des chercheurs engagés dans la construction de modèles de systèmes complexes naturels, où le nombre de données ne peut pas être multiplié à l'envi par des expérimentations répétées et reproductibles. Conséquence : les modèles sur les changements climatiques ne peuvent être que des hypothèses, mises en formes informatiques très sophistiquées mais pleines d'incertitudes quant à leur relation à la réalité ; et il en va de même des prédictions qui en sont déduites.»

  3. Temperature changes: CNRM IPSL A2 B1

  4. Precipitation changes A2 IPSL CNRM

  5. Two major constraints: (1) Energy conservation Earth radiative budget (W m-2)

  6. (2) Angular momentum conservation

  7. Two basic equilibriums: Geostrophic along the horizontal: Hydrostatic along the vertical

  8. Different types of blocking issues, all linked with scale problems and/or multiple nature of the climate system • Feedback mechanisms (WV, Lapse Rate, Clouds, Snow, Soil Moisture, …) : parameterizations + validation using process studies (and campaign, satellite data) • Natural variablity at synoptic scale: monsoon, MJO, ENSO, QBO, • Extreme events • Abrupt unpredrictable events • Link with « science of the impacts »

  9. Strategy Current Skill User Needs 10000 km 1000 km High Spatial Scales Low 100 km 10 km Unpredictable 1 km Day Minute 1 yr Season Week 100 yrs 10 yrs Time Scales

  10. Gastineau, Le Treut, Li, 2008

  11. Uncertainty is largely associated with some key feedbacks …. and a few more (soil mositure, state of vegetation, …)

  12. IPSL (2L22) ERBE

  13. Precipitation modeles, XXI-XXº change DJF [-1.5;0.3;1.5] mm/day Unities : [-15;3;15]% of pp(20c3m)‏

  14. IPSLCM4 Orchid é e LMD ZT LMD ORCALIM Z Atmospheric Circulation Oc é anique Continental surface Circulatio è n Glace de mer sols et v é g é tation STOMATE PISCES é Biog é ochimie et Biochemistry biologie marine Carbon CO2 Carbon INCA Chemistry CH , COV, DMS 4 Gases A é rosols Nutriments & A é rosols A é rosols Sels marins IPSL Earth System Model (CM4) Continents Atmosphere Oceans Physics Carbon Cycle Chemistry

  15. Climate projections on regional and local scales Performance of current AOGCMs (like those from CMIP3) deteriorate when looking at finer temporal and spatial scales which are needed for many impact assessment studies. Global Regional Continental Local Giorgi 2007

  16. IPCC, WG2

  17. Projects may : • Address model /data process studies at different scales • Propose an integrated view of a given region (include social aspects)

More Related