Royal Netherlands Meteorological Institute; Ministery of Infrastructure and the Environment

Publications, presentations and other activities
Reliability of regional climate model trends
2013
by G.J. van Oldenborgh (KNMI), F.J. Doblas-Reyes (ICREA and IC3, Barcelona, Spain), S.S. Drijfhout (KNMI), E. Hawkins (University of Reading, Reading, U.K.),
Abstract
<p>A necessary condition for a good probabilistic forecast is that the forecast system is shown to be reliable: forecast probabilities should equal observed probabilities verified over a large number of cases. As climate change trends are now emerging from the natural variability, we can apply this concept to climate predictions and compute the reliability of simulated local and regional temperature and precipitation trends (1950-2011) in a recent multi-model ensemble of climate model simulations prepared for the Intergovernmental Panel on Climate Change (IPCC) fifth assessment report (AR5). With only a single verification time, the verification is over the spatial dimension. The local temperature trends appear reliable. However, when the global mean climate response is factored out, the ensemble is overconfident: the observed trend is outside the range of modelled trends in many more regions than would be expected by natural variability and model spread. Precipitation trends are overconfident for all trend definitions. This implies that for near-term local climate forecasts the CMIP5 ensemble cannot simply be used as a reliable probabilistic forecast.</p>
Observed trends 1950--2011 in a) GISTEMP temperature (decorrelation scale 1200 km) [K/K] and b) GPCC precipitation [%/K] as regression on the modelled global mean temperature equation (2) (white areas do not have enough data to compute a trend); c),d) corresponding CMIP5 multi-model mean trends; e),f) percentile of the observed trends in the CMIP5 ensemble at the same grid point; g),h) red line: rank histograms for the trends in temperature, precipitation and sea-level pressure North of 45&ordm;S, grey area: the 90% range obtained from the inter-model variations.

Biblographic data
Oldenborgh, G.J. van, F.J. Doblas-Reyes, S.S. Drijfhout and E. Hawkins, Reliability of regional climate model trends
Environmental Research Letters, 2013, 8, 1, 014055, doi:10.1088/1748-9326/8/1/014055.
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