Environmental Systems Science Centre, University of Reading MRC, London, April 5th 2005 The atmospheric hydrological cycle and climate feedbacks: past, present and future Richard Allan Environmental Systems Science Centre, University of Reading

Climate Change How the hydrological cycle responds to global warming is crucial to mankind (e.g. water supply, agriculture, severe weather, ecosystems)

Earth’s Radiation balance and climate S~1367 Wm-2 Thermal IR/LW or Outgoing Longwave Radiation (OLR) Solar/SW (S/4)(1-Albedo) – OLR = 0 (at balance) 2xCO2  ~ 4 Wm-2 less OLR  heating Feedback: response of system is crucial to magnitude and nature of climate change Don’t care about dTs, BUT effect on hydrological cycle likely scales with magnitude of dTs Need complex models to resolve myriad of regional interactions and feedbacks that determine response of the system, but…

Climate Sensitivity (K) How will climate and global water cycle respond to increasing greenhouse gases? IPCC(1990) 2xCO2 sensitivity dTs ~ 1.5 – 4.5 K Stainforth et al.(2004) Nature Need complex models of Earth-atmosphere system to resolve regional interactions between multiple feedback processes Climate Sensitivity (K)

Aims and Strategy Aim Strategy: to reduce uncertainty in climate prediction and climate impacts using EO data to understand the likely response of the hydrological cycle to increased greenhouse gases Strategy: Monitor present-day and past changes in hydrological cycle Identify physical models Uncover previously unidentified processes

Previously unidentified process involving cloudiness and ocean heat storage? An example of possibly unidentified process identified using EO and ocean data. IPCC (2007) in preparation, provided by B.A. Wielicki

Decadal-scale passive microwave data: monitoring column integrated water vapour

Identify physical models Note: Thermodynamic increase in WV  atmospheric LW radiative cooling  increase in global water cycle

water vapour and temperature Increases in water vapour with temperature imply an enhanced atmospheric hydrological cycle water vapour and temperature atmospheric cooling global water cycle

Concluding remarks Timeliness: why now? What is different? EO-data beginning to resolve decadal time-scales Apparent uncertainty in climate model predictions are becoming larger, not smaller! What is different? Encompass entire hydrological cycle – a 5-year challenge Earth-system strategy: analysing interactions between global water cycle, radiative cooling, latent heating and atmospheric circulation using EO data “Fast” and “Slow” feedbacks Regional and regime-dependent interactions

Work plan WP1 – Identification and intercomparison of datasets on hydrological cycle (year 1) e.g. SSM/I, CERES, CMAP, daSilva, CLAUS… Development of surface and atmospheric flux capability WP2 – Spatial and temporal variability (years 1-2) Spatial, daily, seasonal, interannual, ENSO, decadal WP3 – Identification of regional and dynamical regime feedbacks + techniques (years 2-4) WP4 – Identification of physical models (years 3-5) Reduction in uncertainty of climate sensitivity

Links ESSC Meteorology Department – Shine, Hogan Met Office, Hadley Centre Griggs, Ringer ESSC Imperial College Harries GFDL -Ramaswamy ECMWF - Simmonds Morcrette NASA Langley Wielicki, Wong Initial established links from ESSC as part of the project University of Miami - Soden