About the experiments

The overall experiment design is in five parts.

First, a large number of different versions of the global and regional models will be used to simulate the period from 1960 to 2010 using observed changes in sea surface temperatures, sea ice, atmospheric greenhouse gases and aerosols. The simulated climates and patterns of change in weather events from the models will then be compared with observations over the same period to select a range of realistic model versions and document their behaviour. If, for example, we find that a particular version of the model tends to over-do the number of storms, we can take account of this when using this model to forecast future changes in storminess.

The second experiment is to produce a forecast of changes in weather events by the 2020s and 2030s. Using output from many different models with evolving oceans to provide the forecast sea surface temperatures up to this time, the regional model will tell us about the potential changes to patterns of weather events through the next three decades in unprecedented detail. Features such as changes in the likelihood of drought, flood and extreme heat or cold are likely to be of particular interest.

The third experiment returns to changes seen over the last 50 years, and attempts to quantify to what degree these changes can be attributed to the effects of human interference in the climate system. The driving conditions fed into the models are modified to reflect what they would have been like if we had not produced the greenhouse gas and aerosol emissions that we have over the past century. The difference between these simulations and the initial `baseline’ runs will provide the basis for assessing the human contribution to recent weather trends.

The fourth experiment returns to forecast mode but runs beyond the timeline of the second experiment, providing detailed information about changes in weather features in a world 2, 3 and 4 degrees warmer, globally, than today, representing a range of climates that might be encountered towards the end of this century or beyond. This experiment will provide some of the most detailed information to date on regional weather in such possible future worlds, which is essential to assess the range of potential impacts of climate change.

Finally, the fifth experiment looks back into the past – looking at snapshots of the weather at intervals over the past 10,000 years, a period of Earth’s history called the ‘Holocene’. This is the first time large numbers of regional models have been applied to such ‘paleoclimate’ (past climates) simulation: an unprecedented opportunity to explore the evolution of the weather over recent Earth history.

The project team aims to run as many of these experiments as possible, but please note that not all experiments will necessarily be performed for all regions.