In the AR4, the IPCC presented this figure showing the consensus in precipitation projections for the 21st century, designed to be of use to planning for adaptation and mitigation. The coloured regions show where changes are likely to occur. My interest is in the white areas where models cannot agree on the sign of the change. This could mean that half the models predict a large drying and half predict a large increase in rainfall. But, it could also just mean that the changes are small, but that the sign is uncertain.
The figures below show the percentage of GCM consensus that the signal in precipitation change will be smaller than the natural decadal variability in rainfall (S/N < 1) for different seasons and lead times. This could also be of use to planners, indicating that adaptation to natural variability will also adapt to future changes. This helps move from ‘no consensus in a trend’, to ‘consensus in no trend’, which I think was missing from AR4.