Trends in winter warm spells in the Central England temperature record

An important impact of climate change on agriculture and the sustainability of ecosystems is the increase of extended warm spells during winter. We apply crossing theory to the Central England Temperature timeseries of winter daily maximum temperatures to quantify how increased occurrence of higher temperatures translates into more frequent, longer lasting and more intense winter warm spells. We find since the late 1800s an overall 2-3-fold increase in the frequency and duration of winter warm spells. A winter warm spell of 5 days duration with daytime maxima above 13°C has a return period that was often over 5 years but now is consistently below 4 years. Week-long warm intervals that return on average every 5 years now consistently exceed ~13 °C. The observed changes in the temporal pattern of environmental variability will affect the phenology of ecological processes and the structure and functioning of ecosystems.