2 The climate models

A set of global and regional climate models have been set up by the Met Office Hadley Centre. An experimental design has been chosen that allows an estimate to be made of uncertainty of future climate projections.

Here we have combined the spread from the Met Office Hadley Centre models with that from alternative climate models produced by other international climate research institutes.

The Met Office Hadley Centre model ensemble is referred to as the Perturbed physics ensemble (PPE), whilst the international model ensemble is termed the Multi-model ensemble (MME). An understanding of the choice and experimental set up of climate modelling is important because these supply driving information for shelf sea and wave models reported in subsequent chapters. A particularly important aspect of the climate model output with regards to marine projections around the UK is changes in storminess and these are discussed here.

Key Findings

• The available climate models provide suitable driving data with which to force models of extreme sea level (Chapter 3 and Chapter 4), waves (Chapter 5) and shelf hydrography (Chapter 6). However, since the driving models for the marine scenarios may not sample the full range of known uncertainties, each uncertainty range quoted should be regarded as a minimum range.

• The ensemble of Met Office Hadley Centre models (PPE) typically shows a slight weakening and southward movement of the storm track over the UK.

• The ensemble containing models from other climate research centres (MME), typically shows a greater increase in storm intensity, but less latitudinal movement in track position. In contrast to the PPE, a MME latitudinal shift can be either northward or southward.

Introduction

The marine scenarios describe projected climate changes in the shelf seas around the UK. However, since the enhanced greenhouse effect (Figure 2.1), which drives these changes, involves the accumulation of radiatively absorbing gases in the atmosphere and takes place at a global scale the maritime models must be connected to climate models.