Temporal variations of trends in the Central England Temperature series

Variations in trend rates of annual values of the Central England Temperature series (CET) over the period1659-2017 were analysed using moving windows of different length, to identify the minimum period in which the trend expresses a climate signal not hidden by the noise produced by natural variability. Trend rates exhibit high variability and irregular shifting from positive to negative values unless very long window lengths (of 100 years or more) are used. In general, as the duration of the length of the temporal window analysed increases, the absolute range of the trend rates decreases and the signal-to-noise (S/N) ratio increases. The relationship between the S/N ratio and the window length also depended on the total length of the series, so high S/N values are achieved faster when shorter time series are considered. This prevents suggesting a minimum window length for undertaking trend analyses.A comparison between CET and the average continental series in the Berkeley Earth Surface Temperature (BEST) database in their common period (1753-2017) repeats the patterns described for 1659-2017, although the average values of the rates, ranges and the "threshold period" in years change, and are more variable in CET than in BEST.Analysis of both series suggests that the recent warming started early and can be linked to the recovery of temperatures after the Little Ice Age. This process has characterised by progressively increasing trend rates, but also includes periods of deceleration or even negative trends spanning less than 50 years. The behaviour of the two long-term temperature records analysed agrees with a long-term persistence (LTP) process. We estimated the Hurst exponent of the CET series to be around 0.72 and 0.8, which reinforces the LTP hypothesis. This implies that the currently widespread statistical framework assuming a stationary, short-memory process in which departures from the norm can be easily assessed by monotonic trend analysis should not be accepted for long climatic series. In brief, relevant questions relative to the recent evolution of temperatures such as the distinction between natural variability and departures from stationarity; attribution of the causes of variability at different time scales; determination of the shortest window length to detect a trend; and other similar ones have still not been answered and may require adoption of an alternative analytical framework.

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 time series 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 two- to threefold increase in the frequency and duration of winter warm spells. A winter warm spell of 5 days in duration with daytime maxima above 13°C has a return period that was often over 5 years but now is consistently below 4 years. Weeklong 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.

Central England Temperatures Data Set: Key to Understanding the Cause of Climate Change

An analysis of Little Ice Age temperatures, using the Central England Temperature dataset (HadCET) shows that all temperature decreases were due to dimming sulfurous emissions from volcanic eruptions. There was no cooling effect, at any time, from the absence of sunspots.

Long-period weather observations elsewhere in the British Isles and Europe

This chapter summarises other long-period weather observations from both the British Isles and Europe. The Radcliffe Observatory possesses the longest continuous series of weather records in Britain for one site: the first observations date from the mid-1760s, with unbroken daily temperature records since November 1813. It includes references to Gordon Manley’s Central England Temperature series. There are brief descriptions of the longest-running weather stations in Europe, including Uppsala and Stockholm in Sweden, Padua and Milan in Italy, Hohenpeissenberg in Germany, and the British observatories at Kew, Armagh and Durham, many (like Oxford) starting life as astronomical observatories in the eighteenth or early nineteenth centuries. The chapter ends with a brief comment as to why such long weather records remain important in the present day.

Oxford’s urban growth and its potential impact on the local climate

This chapter deals with the growth of Oxford since 1767 and assessment of the potential influence of the expanding urban area on the temperature record from the Radcliffe Observatory, using long-period data from a semi-rural site at Rothamsted (Hertfordshire) and a more recent 3-year comparison with records from nearby Wallingford to assess the extent of, and changes in, Oxford’s urban heat island. The urban heat island effect remains small but is shown to have increased in magnitude in recent decades, and is likely to affect the homogeneity of the Oxford temperature record. In addition, the chapter provides a comparison of the data from the Radcliffe Observatory with that from the Central England Temperature series.