A Tree-ring Stable Carbon Isotope Reconstruction of Summer Sunshine for the United Kingdom (1523 – 2000 CE)

Anthropogenic actions have altered the Earth’s climate system. To help improve future predictions of Climate Change, tree-rings can be used as a climate proxy to extend modern weather records back in time to provide a greater perspective. For this purpose, this thesis aimed to produce the first oak latewood stable carbon isotope (δ13C) reconstruction for the UK. Alpha cellulose was extracted from >18,000 latewood bands to produce one of the largest isotope datasets in the literature. The initial dataset was found to have a compromised common signal, and examination of the individual records highlighted anomalous events. It was hypothesised that both natural disturbances and forest management practices were the cause. It was concluded that the raw dataset would not be suitable for a climate reconstruction, but if the disturbances could be removed, then a reconstruction maybe possible. A homogenisation methodology adapted from climatology was tested and calibrated. It was found that the approach could remedy the disturbances in the δ13C dataset. This improved the common signal of the records to a level traditionally deemed suitable in dendroclimatology for climate analysis. It was assumed that this reflected an improvement in the extractable climate signal. Importantly, the method did not require the need for detrending or filtering, which would have compromised the long-term climate signal. Using the homogenised record, and a baseline non-treated chronology for contrast, climate analysis was conducted. Comparisons of the two masters with climate variables, demonstrated that the homogenised record was superior. With the results justifying a scaled reconstruction of late summer (July and August) solar radiation. The reconstruction covered 1523 – 2000 CE and was interpreted to indicate changes in cloud coverage. The reconstruction was also considered alongside reconstructions of temperature and precipitation for the region. The Little Ice Age was dominated by a time of increased sunshine and low temperatures. Some of the driest conditions in the whole reconstruction were also found during this period. However, the Little Ice Age also saw two periods of suggested storminess, marked by high precipitation and cloud coverage. The modern warm period (post-1800 CE) was characterised by increased temperatures and below average precipitation. Initially, the modern warm period was the cloudiest in the reconstruction, however, by the end of the 20th century, solar radiation approached the levels seen during the Little Ice Age. The UK solar radiation reconstruction reflected those from across Europe, suggesting a common forcing mechanism