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Climate Change Across The Macaronesian Geographical Region, 1850 - 2100

Cropper, Thomas E (2015) Climate Change Across The Macaronesian Geographical Region, 1850 - 2100. PhD thesis, University of Sheffield.

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Abstract

The Macaronesian geographical zone extends from 10-40°N, 325-355°E and primarily includes the island chains of the Azores, Madeira, the Canary Islands and Cape Verde. This thesis presents a wide-ranging analysis of the physical climate and oceanography of the region back to 1850, in order to place recent climate change within a historical context. Subsequently, this thesis presents the most complete documentation of the physical climate of Macaronesia in the English language literature. One of the main outputs of this thesis is the creation of a long-term, monthly surface air temperature record for each island chain (from 1865 for the Azores and Madeira, 1885 for the Canary Islands and 1895 for Cape Verde). These temperature records exhibit generally coherent patterns of variability, and a post-1976 increase in temperature - most probably reflecting an anthropogenic climate signal - is the most ubiquitous, significant rise (or fall) in the record. Precipitation variability is also analysed, although only trends from Cape Verde are particularly significant, where a slight precipitation recovery - after the turn of the Twenty-first Century since drought conditions in the mid-late Twentieth Century - is apparent. Climatological extreme indices, based on calculations that assimilate daily temperature and precipitation data, were also analysed for the recent past (1979-2011) and point towards warmer conditions. An assessment of potential future changes in the mean state and extreme indices of climate across the islands by the end of the Twenty-first Century is provided. Warming magnitudes for the 2071-2100 period range between 0.8-3.0°C above the 1976-2005 mean temperature. Precipitation is expected to decrease across the Canary Islands and Madeira, whereas the Azores is expected to experience more extreme precipitation events and precipitation changes across Cape Verde are uncertain. In addition to the analysis of temperature and precipitation changes, a daily North Atlantic Oscillation index extending back to 1850 using historical sea-level pressure data from the Azores was constructed. The temporal length of this newly created index exceeds the length of any previously available long-running, daily-resolution series by a hundred years and should be of great value to researchers across multiple disciplines. The spatial and temporal variability of the North Atlantic Oscillation was analysed, finding an increase in post-2004 winter variability, alongside a post-1991 negative summer trend. A novel method to characterise the strength of the Trade Winds by using data from the Azores and Cape Verde was also developed. The newly-defined Trade Wind index has been steadily increasing since 1973. An additional analysis was a comprehensive overview and reconciliation of multiple data sources to answer the question of whether coastal upwelling has been increasing across the Canary Upwelling Ecosystem along the northwest African coastline. This analysis determined that the Bakun upwelling intensification hypothesis developed in 1990 appears to be realised in the summertime coastal upwelling indices. The North Atlantic Oscillation was discovered to be strongly related to upwelling magnitudes for all seasons except summer, in addition to exerting a strong control on temperatures and precipitation across the three northernmost Macaronesian island chains. The small-scale features affecting island climates and the large-scale modes of variability that influence the Macaronesian region are also discussed.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Social Sciences (Sheffield) > Geography (Sheffield)
Identification Number/EthosID: uk.bl.ethos.651271
Depositing User: Mr Thomas E Cropper
Date Deposited: 17 Jun 2015 11:38
Last Modified: 03 Oct 2016 12:10
URI: http://etheses.whiterose.ac.uk/id/eprint/9244

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