Relationship between

global mean sea-level, global mean temperature and heat-flux in a

climate simulation of the past millennium

Hans von Storch, Eduardo Zorita and F. González-Rouco

GKSS Research Centre, Geesthacht, Germany

Universidad Complutense Madrid

Factors governing 20th century global annual sea-level rise:

Thermal expansion of the ocean

Mass balance of land ice

Management of natural and artificial aquifers

Factors governing 20th century global annual sea-level rise:

Thermal expansion of the ocean

Mass balance of land ice

Management of natural and artificial aquifers

Estimated by climate models, though uncertain (20-60 cm rise for 2100 )

Uncertain, not estimated by current global climate models

d (sea-level)/dt ~ Temperature

sea-level rate

temperature

Rahmstorf 2007

<-200 years->

Semi-empirical methods linking global temperature and sea-level (rate)

Rahmsorf, 2007; Grinsted et al, 2009

Idea:

-design a statistical model with global temperature as

predictor to infer global sea-level (rate) changes:

SL (t) = function (global T and some parameters)

-Estimate the value of the parameters by fitting F to

the observational record

-Predict SL(future) from the simulated future global T

The risk of correlation analysis with non-stationary series

global sea-level rateglobal mean temperature

Rahmstorf 2007

The risk of correlation analysis with non-stationary series

global sea-level rateglobal mean temperature

The observational record is short and shows a strong trend

How to test whether the estimated parameters are correct?

Test the whole idea in the virtual reality produced by global coupled

atmosphere-ocean model for long periods of time (with temperature ups

and downs -> more real degrees of freedom)

Advantage: everything is known

Disadvantage: land ice melting is poorly represented

Global climate simulation of the past millennium

Model ECHO-G (but results from HadCM3 simulation will be also shown)

ECHO-GModel used in IPCC AR4

Atmospheric model ECHAM4

19 levels, 3.75x3.75 deg res.

Ocean model HOPE20 levels, 2 x2 deg res.

Flux correction appliedspatial average zero

How realistic is the simulation of the thermosteric sea-level variations?

Energy-balance-upwellling-diffusion modelECHO-G

full-blown IPCC climate model

Realistic simulation of recent thermosteric sea-level rise

Possible predictors to determine sea-level rise

The relationship between global T and global sea-level rate of change dH/dt

is not stable through time

Unstable relationship between global T and global sea-level rate through time

More stable relationship between global T rate and global sea-level rate

Conclusions

-The relationship between global temperature and thermosteric

sea-level can be more complex than a simple linear regression

-Heat flux into the ocean seems to be a good predictor for the

thermosteric sea-level rise.

-To explore the relationship between external climate forcing and

sea-level rise