Aren't the uncertainties too large to be of use?
By providing a range of results rather than single best estimate values, and the inclusion of an assessment of uncertainty, users get a much more detailed picture about the level of confidence they can have in different outcomes. It also encourages a flexible approach to dealing with a range of future climates.
Attaching probabilities to different parts of the range of outcomes helps you identify which parts of the range are more likely, and which less so, and helps to put a large range of results in context.
The probabilities cannot include every aspect of uncertainty. To ensure that users understand what has and has not been factored in to produce the results, guidance on the methodology can be found in Chapter 2 of the Climate change projections report.