Issues in the interpretation of climate model ensembles to inform decisions

Abstract

There is a scientific consensus regarding the reality of anthropogenic climate change. This has led to substantial efforts to reduce atmospheric greenhouse gas emissions and thereby mitigate the impacts of climate change on a global scale. Despite these efforts, we are committed to substantial further changes over at least the next few decades. Societies will therefore have to adapt to changes in climate. Both adaptation and mitigation require action on scales ranging from local to global, but adaptation could directly benefit from climate predictions on regional scales while mitigation could be driven solely by awareness of the global problem; regional projections being principally of motivational value. We discuss how recent developments of large ensembles of climate model simulations can be interpreted to provide information on these scales and to inform societal decisions. Adaptation is most relevant as an influence on decisions which exist irrespective of climate change, but which have consequences on decadal time-scales. Even in such situations, climate change is often only a minor influence; perhaps helping to restrict the choice of 'no regrets' strategies. Nevertheless, if climate models are to provide inputs to societal decisions, it is important to interpret them appropriately. We take climate ensembles exploring model uncertainty as potentially providing a lower bound on the maximum range of uncertainty and thus a non-discountable climate change envelope. An analysis pathway is presented, describing how this information may provide an input to decisions, sometimes via a number of other analysis procedures and thus a cascade of uncertainty. An initial screening is seen as a valuable component of this process, potentially avoiding unnecessary effort while guiding decision makers through issues of confidence and robustness in climate modelling information. Our focus is the usage of decadal to centennial time-scale climate change simulations as inputs to decision

Modelling climate impact on floods with ensemble climate projections

“…The use of ensembles of models and techniques is one way to get a handle on and to represent these uncertainties (e.g. Murphy et al, 2004;Stainforth et al, 2007;Cloke and Pappenberger, 2009;Weisheimer et al, 2011), and an ensemble of ensembles can be termed a grand ensemble .…”

An alternate approach to assessing climate risks

“…As a result, the possible range of climate changes might not be fully explored if an analysis relies exclusively on climate projections. Instead, climate model projections scope a "minimum range of irreducible uncertainty" [Stainforth et al, 2007]. In other words, the range of projections represents some of the uncertainty in the possible range of future climate but not the full range of possible climate changes.…”

Ensembles and probabilities: a new era in the prediction of climate change

“…There is a significant area of research in the impacts or applications of climate change which takes the raw climate information and uses further modelling techniques to produce societal-relevant information (New et al 2007;Stainforth et al 2007b). Impacts models are diverse and examples are available in the prediction of river flow and other hydrological variables, crop yield and energy demand.…”

“…Resolving the three-dimensional flow of the ocean and atmosphere in the finest grid practicable and including representations of unresolved sub-grid-scale processes, they are the most computationally expensive. Standard supercomputer resources can be employed to produce ensembles with tens to hundreds of members (Murphy et al 2007;Tebaldi & Knutti 2007): much larger ensembles have only been possible using highly novel computing techniques (Frame et al 2007;Stainforth et al 2007b). They are the only way of providing predictions at regional scales and for 'exotic' variables such as extreme precipitation, for example.…”