What’s the difference between Predictions and Projections?

Science Highlights

Kirtman, et al 2013: Near-term Climate Change: Projections and Predictability. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Climate scientists use the terms ‘predictions’ and ‘projections’ to describe two different kinds of information that are both important on decision timescales. ‘Predictions’ describe the forecasted climate for the next few months or years, which are strongly influenced by natural year-to-year or multi-year cycles of natural variability.  We refer to the models used to make decadal predictions as ‘initialised’ because the most recent, observed climate conditions are important for forecasting the next few years. On the other hand, ‘Projections’ refers to the information for several decades ahead, which tell us how the climate might respond in the longer term to scenarios of greenhouse-gas emissions and associated socio-economic pathways.

Predictions and projections are generated using different modelling systems, reflecting the different factors involved, which makes it difficult combine the relevant information for a few years out all the way through to a few decades.  This is why EUCP is pioneering approaches that will allow users to use more seamlessly the information from initialised climate predictions and climate projections to span these different timescales.