Combining information from decadal predictions and climate projections to phase in climate variability

Information about the near-term future climate evolution over Europe is available from a range of sources. In particular, on the EUCP target time scales of the next 40 years, global initialised (decadal predictions) and non-initialised (projections) model simulations, together with regional modelling data, form the basis of our research in Work Package 5 of EUCP. Global decadal predictions are updated every year by making use of the latest oceanic and atmospheric observations for their initialisation and run one decade into the future. In contrast, global climate projections are run once (e.g. a few years ago for the latest Coupled Model Intercomparison Project, CMIP6) and cover all of the 21st century. High-resolution regional model simulations are available for selected time slices of future projections.

For a user interested in the likely climate over a specific geographical region, the plethora of climate data from these different sources of future model simulations can be confusing. The different data sets may not agree on the outcome and there is some ambiguity as to which data to use if there is overlapping availability. Within WP5, we have thus been studying how information from decadal predictions and climate projections can be combined such that the advantages of each can be gathered without losing valuable information. One area of research explored the feasibility of constraining the variability of ensembles of future climate projections using the latest decadal predictions. We were able to demonstrate that, in the case of predicting temperatures over the North Atlantic, the forecasts’ quality improved due to these constraints even after the 10 years for which decadal predictions were available (see here for more). Another novel constraining method developed within WP5 takes into account global patterns of climate variability. It was shown that this approach was able to improve climate projections of the following 20 years. In addition to constraining methodologies, work is also ongoing to explore the strengths, limitations and practicalities of seamlessly merging initialised predictions and non-initialised projections.