Imposed ozone calculationsQualitatively same behaviour in all models (which qualitiatively agrees with the observations).

Significant quantitative differences.

Radiation schemes?

Background ozone climatologies?

Care in comparing models with obs

Imposed greenhouse gas calculationsQualitative agreement, but surprising quantitative disagreement in upper stratosphere.

Non-CO2 greenhouse gases can’t explain.

Gas changes well contrained.

Presumably radiation codes?

Don’t compare models with obs!

SPARC Water Vapour Assessment (2000)Northern midlatitude trends

Imposed water vapour calculationsTwo classes of calculation

Global HALOE and Global Boulder!

This dominates the model differences.

Note especially the lower stratosphere

Don’t compare models with obs!

Relevance to understanding

forcing mechanisms and attribution

Adapted from Shine et al. QJRMS, 2003

Understanding stratospheric temperature trends

32 km

18 km

Coupled model calculations (O3, ghg, H2O?)

Spread in trends is no greater in coupled runs than in “imposed” runs, despite extra degree of freedom.

Disagreement with observations in middle and lower stratosphere.

Compare models with obs!

An attempt at a “synopsis” Upper stratosphere “OK”

Mid stratosphere – models overestimate cooling.

Why? “Error bars”? Ozone profile? Temperature data? “Linearised” view? Missing mechanism?

Lower stratosphere – (significant) role for water vapour?

Compare models with obs!

Imposed ozone changes

Tendency for GCMs to have smaller latitudinal gradient than FDH models.

Clear gap between observations and models in Northern Mid-latitudes at 50 hPa

Imposed Greenhouse Gas Changes

Most interesting aspect is GISS model response is quite different to all other GCMs in the intercomparison – does it have an extra degree of freedom, e.g. via its gravity wave scheme??

Coupled Models

Spread in models and no consensus even in the sign of the temperature change. High southern latitudes is the only “consensus” region.

Hint that coupled models underestimate 50 hpa cooling too.

Zonal-mean conclusions

• At 100 mbar, agreement between observations and models generally good with ozone change alone .. adding impact of water vapour improves agreement

• At 50 mbar, ozone incapable of explaining mid-latitude trends – would require considerable water vapour contribution to explain … or does it have a dynamical cause?

Where next?

• This comparison limited – concentrated on annual means and was to some extent an apples-and-oranges comparison

• Single model tests of impact of uncertainties in (e.g.) ozone profiles? Transient runs? Multi-model intercomparison of radiative codes (benchmarks are available)?

Annual-mean 11-yr Solar Cycle Signal in Temperature from ECMWF Reanalysis

Crooks and Gray, 2005

50 km

20 km

S N

Changes in ozone from solar minimum to maximum

Results…

• Blah

Temperature Change solar min to max [K] using ozone distribution shown earlier

Comparison with SSU

• Simplified solar cycle

• Superimposed on a linear trend