Why bother using climate projections when we know they are not perfect?

As is the case with most process models, no climate model is perfect. All models are only a representation of the real world and have inherent assumptions and limitations. However, the ability of models to represent the climate is improving over time, and we can test their reliability to a certain extent.

In detail

There is considerable confidence that climate models can provide reliable estimates of future climate change. This confidence comes from the fact that models use fundamental physics and chemistry to simulate processes within the climate system, and from their ability to reproduce the current climate and past climate changes. Confidence in model estimates is, however, higher for some climate variables (e.g. temperature) than for others (e.g. precipitation).

In UKCP09 each model variant has been weighted based on their performance of modelling past and current climate, and these results are factored into the resulting probabilities resulting from the method. An explanation of the assumptions and limitations behind UKCP09 will also be available to users. The UKCP09 projections are designed to make modelling uncertainty clear to users, and encourage them to assess their own attitude to risk. UKCP09 projections are designed to make more transparent the uncertainties of projecting changes in the climate system, which correspondingly allows for more robust decision-making.