Western-European cold spells in present-day and future climate

Post date: Oct 18, 2014 6:46:28 PM

Wednesday, February 1, 2012. Climate is different everywhere. Given this notion it often pays off to scale the local climate variables using local mean and standard deviation. This then allows a better comparison between different locations. The same exercise can be undertaken to compare present-day and future climates. This approach has been undertaken for Western European cold spells. The results have now (finally) been published in Geophysical Research Letters with interesting results (doi:10.1029/2011GL050665).

Cold spell evolution. (left) Composite evolution centered at time of minimum. Horizontal lines denote the temperature threshold. Confidence intervals estimated using bootstrap. The dark (light) shading indicate confidence intervals (95%) for a 17-member (1-member) bootstrap. (right) As in the left plot but after scaling but mean and standard deviation. The grey band displays a confidence interval for the difference.

Abstract: “This paper discusses western European cold spells (where temperature falls below the 10% quantile of the winter temperature distribution) in current and future climate. It is demonstrated that many of the projected future changes in cold-spell statistics (duration, return period, intensity) can be explained by changes in the mean (increase) and var- iance (decrease) of the winter temperature distribution. After correcting for these changes (by subtracting the mean tem- perature and by dividing by the standard deviation), future cold-spell statistics display no major changes outside esti- mated error bounds. In absolute terms however, the future cold spells are projected to become $5°C warmer (and remain above freezing point), thus having a significant cli- matic impact. An important contributor to the projected future decrease of temperature variance is shown to be the reduction of the mean zonal temperature gradient (land- sea contrast). These results have been obtained using a 17-member ensemble of climate-model simulations with current and future concentration of greenhouse gases.”