Climate projections are a key part of the climate adaptation research toolbox. The most likely direction and magnitude of change under a given emissions pathway can strongly inform adaptation plans. Also, robust decision making using a risk management approach needs to consider ‘low-probability, high-impact’ (or ‘worst case’) outcome, as well as the ‘best case’ outcome as well. The range of results from a set of climate models can be used to indicate the range of possible climate changes for a given emissions pathway, and the Climate Futures tool can be used to explore this*. Additionally, it is useful to use various other lines of evidence such as physical theory to explore limits to change. This exploration may suggest changes outside the range of models, or alternatively we may be able to narrow the range of results from climate models.

Here we examine key lines of evidence regarding temperature projections for Australia, and rainfall projections for southern Australia to explore limits to change, and define some best and worst cases. Analysis of climate sensitivity suggests that temperature changes above and below the modelled range are possible, and analysis of atmospheric circulation features suggest that we can reduce the current range of projected rainfall change. We outline these limits and discuss what they mean for climate adaptation planning.

* See: www.climatechangeinaustralia.gov.au