Professor Myles Allen CBE FRS

Abstract:

We investigate the atmospheric response to doubled CO2 and stratospheric ozone depletion in three versions of a general-circulation model with differing vertical resolution and upper-boundary heights. We find that an approximate doubling of the vertical resolution below 10 hPa reduces the temperature response to a doubling of CO2 from 3.4 K to 2.5 K. Much of this difference is associated with changes in the cloud response. All model versions show an increase in the Arctic Oscillation index in response to a doubling of CO2, but the increase is no larger in the model with an upper boundary at 0.01 hPa than in the standard model with a top level at 5 hPa. All models also show general stratospheric cooling in response to doubling CO2. However, unlike some other authors, we find no cooling in the Arctic winter vortex below around 10 hPa in the stratosphere-resolving model, and a weakening of the zonal winds throughout this region. This effect is due to enhanced upward propagation of planetary waves from the troposphere, and is an effect found only in the northern hemisphere, probably because of its larger zonal asymmetries. All models show a small but significant surface cooling in response to a reconstruction of 1998 stratospheric ozone depletion, and an increase in the Antarctic Oscillation index in the southern summer. The cooling extends through most of the atmosphere, and reaches a maximum in the region of the Antarctic ozone hole in November and December.

Abstract:

The development of the demonstration release software which solves the modeling tasks such as climate simulation, was discussed. The package was designed in a modular fashion to simplify upgrades of separate sections without requiring large downloads. One central server will initially manage the ensemble of climate models and the data generated. The server implementation is based on a standard web servers and mySQL database.

Abstract:

We assess the robustness of previous optimal detection and attribution studies considering zonal-mean temperatures. Principal results, which have consistently pointed towards a demonstrable anthropogenic influence on recently observed upper air temperatures, are confirmed. Importantly our detection results are not critically dependent on the inclusion of stratospheric as well as tropospheric temperatures. We find that detection is dependent on input field pre-processing choices, and on the choice of detection algorithm. There are a number of cases where either no signals are detected, or results fail a consistency test.