Climate policy needs to be based on the best available climate science, including projections of temperature, average annual rainfall and, most importantly, measures of rainfall variability (ie flood, drought and changes in seasonality). Climate scrutiny reviews available sources and interprets them in a way that can be used for policy analysis. The key sources are usually

• Global climate models: especially IPCC Assessment Reports and Special Report on Extreme Events
• Downscaled models: where these are available, especially PRECIS studies
• Recent trends: climate data over the last few decades, if available
• Other evidence: including historical sources, which gives clue about the range of possible outcomes, especially for more radical changes

These three sources are often remarkably consistent but, where there are differences, the quality of each resource needs to be assessed and a headline scenario developed based on a triangulation of  each source.