Project 9 (WP2): Grand Challenge on clouds and climate sensitivity

Project lead: Sandrine Bony

Post-doctoral researcher: Kenji Izumi

Project Start/End: September 2014 – August 2015

Since 2014, the L-IPSL supports activities related to the Grand Challenge on “Clouds, Circulation and Climate Sensitivity” (Bony et al. 2015), which is one of the six Grand Science Challenges (GCs) defined by the World Climate Research Programme (WCRP) for the next decade. This support takes several forms, ranging from:

  • Funding post-doctoral researchers (Kenji Izumi and Marco Gaetani partly, see Projet #8 )
  • Supporting visits of foreign researchers for seminars (e.g. Isaac Held from NOAA/GFDL) and/or research collaborations (e.g. Julia Hargreaves from BlueSkiesResearch and Aiko Voigt from Columbia University)
  • Supporting the participation of IPSL researchers to meetings or workshops directly related to this GC, such as the Ringberg workshop (Mar 2014) on the definition of the science questions around which the GC will focus over the next years, a workshop (Mar 2015) on reconciling Climate Sensitivity estimates from instrumental records, paleoclimatic data, comprehensive climate models, or process, or an MIT/Lorenz Center workshop on the role of water in the climate system (Feb 2014).

The post-doctoral work of Kenji Izumi, started on Sept 2014, has two main objectives: One is to identify robust relationships, in a multi-model context, between changes in tropical precipitation and large-scale atmospheric circulation in CMIP5 simulations of past (Last Glacial Maximum and Mid-Holocene) and future climates (1%CO2, abrupt4xCO2); preliminary results indicate that a generally consistent change in circulation between warm and cold climates which can be well explained by changes in mean temperature and in equatorial heat transport between the two hemispheres, but they also indicate a weak correlation in terms of magnitude (Izumi et al. 2015). The second objective is to explore the role of cloud-radiative effects on the northward shift of the ITCZ and African monsoon during the Mid-Holocene, and investigate how much the persistent inability of climate models to reproduce a shift consistent with observations could be due to a deficient representation of model clouds. Short simulations with the LMDZ GCM indicate some impact of cloud-radiative effects on the magnitude of the ITCZ shift, but longer simulations need to be run to ensure the statistical significance of the result.

Position offer and results (January 2017 update)