Present day climate modelling – its status and challenges Ulrich Cubasch Institut für Meterologie Freie Universität Berlin sponsored by BMBF and EU

Lectures Present day climate modelling – its status and challenges Development of a climate m odel Projection of future climate change Modelling past climate

Gliederung Introduction The forcings Simulation of the Eemian Simulating the climate of the last 1000 years Scenario calculations Summary Outlook

Temperature-Reconstruction (treerings, corals, ice and sediment cores, historical evidence) of the temperature of the northern hemisphere from the year 1000 bis 1999 and instrumental temperature from 1902 to 1999 The „Mann et al“- curve (hockey-stick)

Temperature CO 2 CH 4 today The Vostock ice core

Scientific questions To what extend does a change in radiative forcing (sun, volcanoes, greenhouse gases, aerosols) influence the climate? –How does solar induced climate variability compare with anthropogenic influences? –How sensitive is the climate system? –How will the climate of the future look like? –Can a climate model simulate the historic climate variability? Does it confirm the reconstructions? Can it be used to substitute and/or assimilate proxy-data? –Can the climate model simulate paleo-climatic conditions like ice ages and warm periods as well as the transition between warm and cold stadials? Does it confirm the climate archives? Can it be used to substitute and/or assimilate proxy-data?

The forcings

The climate system External Forcing

Orbital parameter

Change of solar input by orbital parameters obliquity  tilt of the earth axis excentricity precession ~100 ky ~ 23 und 19 ky ~41 ky precession excentricity precession obliquity

Solar variability

Composite solar flux measured by satellites

Yearly averaged solar sunspot number

The solar forcing anomaly reconstructed by 3 different methods

Constituents of the atmosphere

Modelling

…with Earth? or …in the computer? climate change experiments

The physical laws It is assumed that the atmosphere follows physical laws: the Newtonian equations of motion (for the wind fields) the laws of thermodynamics ideal gas equation the continuity equation for mass

The grid representation of a 3-D model

Model Resolutions

Model validation

Validation By comparison of the mean state By comparison of the energy and momentum balance By comparison of the variability By comparison of the hydrological cycle By comparison of the processes (cyclons etc.) By reactions to observed sea-surface temperature changes

model error surface temperature DJF zonally averaged flux corrected not flux corrected CMIP

Simulations from past to future

Simulations of 125 ky BP (Eemian) and 115 ky BP

125 ka bp 115 ka bp Temperature CO 2 CH 4 today

Parameters of the simulations Eemianpresent- 125k115kday CO 2 [ppm] CH 4 [ppb] N 2 O [ppb] Eccentricity Obliquity Precession

125 ky BP 115 ky BP The radiation anomaly compared to present day

July temperature change 125 ka bp F. Kaspar Model Velichko et al., 1992 Reconstruction

125 ka bp 115 ka bp The near-surface temperature change (annual mean)

Thickness of snow in summer [m] F. Kaspar, K. Prömmel 125 ky BP (Eemian) 115 ky BP

Simulations of the last 1000 years

+ = Volcanism Solar Radiation Effective Forcing

Experiments 1. Erik starting at the year 1000  ECHO-G I 2. Columbus starting at the year 1500  ECHO-G II

Zorita et al, 2004 The solar and volcanic forcing and the model response Forcing Temperature- Response Trend

Comparison of modelled and reconstructed temperatures

A comparison with the Hadley-centre simulation HADCM nat. forc. Columbus Erik

Scenario experiments

The information chain leading to a climate projection

The globally averaged change of the near surface temperature relative to the years , Simulated with coupled ocean atmosphere models A2 B2

The annually averaged change of the near surface temperature for the years relative to the years , simulated by globally coupled ocean-atmosphere models for the A2-scenario

The annual mean change of temperature (map) and the regional seasonal change (upper box: DJF; lower box: JJA) for the scenarios A2 and B2

The temperature change for all SRES marker scenarios (simulated by a simplified model)

The temperature evolution of the last 1000 years and the projections for the next 100 years

Stott et al, Nature, 2002 Probability density function for different scenarios and time- intervals, as calculated by HADCM

The projected sea level change

The ocean conveyor belt circulation THC

The change of the thermohaline circulation in the North Atlantic for the IS92a scenario

Summary The paleo climate can be simulated with the coupled ocean-atmosphere models previously employed for climate change predictions The model simulates the Eemian and the transition to an ice age Simulations of the climate of the last 1000 years show a larger amplitude in the temperature variability than the proxy reconstructions The models predict a climate change between 1.4 and 5.8 K. If the uncertainty is taken into account, it might well extend beyond 8 K

Outlook

Probabilistic approach

Stott and Kettleborough, 2002 Probability density functions of temperature change simulated with the Hadley Centre model

Allen & Ingram, 2002 Probability density distribution of climate projection

Model improvements too many to name them all Here is just one example – the role of the stratosphere

The two states of the North Atlantic oscillation (NAO) high index low index

OCEANOCEAN TROPOSPHERETROPOSPHERE STRATOSPHERESTRATOSPHERE Pattern: AO & AAO Pattern: NAO & PNA ENSO & PDO Pattern: THC & GC Feature: SST-Anomalies Feature: Blockings over Pacific and Atlantic Feature: Midwinter warmings Forcing: QBO ozone solar-cycle Forcing: Aerosols, gravity waves Forcing: Seaice C o u p li n g Baldwin,'02 Kodera,'00 Shindell,'99 Hurrell,'01 Schlesinger,'00 ? Blessmann The coupling between ocean-atmosphere-stratosphere

The coupled ocean-troposphere- stratosphere model EGMAM ● atmosphere: ECHAM4 ● ocean: HOPE - G ● coupled: ECHO - G OCEAN TROPOSPHERE (STRATOSPHERE) STRATOSPHERE (MESOSPHERE) Level Blessmann

The power spectrum of the 19 level and the 39 level coupled ocean-atmosphere model for the NAO-index NAO Blessmann with stratosphere without stratosphere observations

Ultimate Goal

Technical infrastructure Earth simulator - hardware (Japan) ESMF (Earth system modelling facility) – software (USA) PRISM (PRogramme for Integrated earth System Modelling) – software – European Union

PRISM System - General principles - Standard physical interfaces - System architecture - Coupler and I/O - Software management - Vizualisation and diagnostics - GUI interface - Configuration editor - Diagnostics outputs The participating models The science : The technical developments: The users: - Atmosphere - Atmos. Chemistry - Ocean - Ocean biogeochemistry - Sea-ice - Land surface

On going PRISM / ESMF collaboration Coupling infrastructure Supporting software User code Running environment PRISM ESMF Earth System Model

Scientific projects ENSEMBLES (EU-Project) 70+ partners –Workpackage RT2A: climate change experiments as suggested by IPCC Climateprediction.com (NERC-project, UK) –Climate change experiments on home PC‘s, similar to

futurissimo Comprehensive simulation of the Holocene Simulation of the last glacial-interglacial Paleo-data assimilation