The possible effects of climate change on the spatial and temporal variation of the altitudinal temperature gradient and the consequences for growth potential in the uplands of northern England
This thesis studies the potential impacts of lapse rate changes on the altitudinal thermal resource gradient in Northern England and hence of climate change on upland climate. The extreme marginality of the Pennine uplands in terms of climatic potential for plant growth is explained by reference to the maritime climate. Because the ground-based temperature lapse rate controls the altitudinal thermal resource gradient, the variation of daily temperature lapse rates by season and airflow is described, using 22 stations ranging from 8 to 847 metres above sea-level. Multiple regression models developed for each airflow in each month successfully describe surface temperature variation in most cases. Such models are used as a basis upon which to describe altitudinal variations in growing season parameters such as accumulated temperatures and frost frequency, for the present climate. Airflow scenarios, based on the regression models, describe the effects of changes in relative frequencies of airflow patterns. The altitudinal gradient in, and absolute values of, growing season parameters depend strongly on relative frequencies of Atlantic westerlies and more blocked conditions. Assuming the annual l000 dºC (degree-day) isotherm to represent the altitudinal limit to agricultural cultivation, individual annual elevations between 1801 and 1990 vary by over 300 metres. Extreme sensitivity to the circulatory pattern is also illustrated. Effects of temperature variability within airflows are at least as strong as those of mean conditions in many cases. The use of General Circulation Model output (UKHI 2 times C0(_2)) leads to strong changes in climatic potential. For example, few areas retain an annual temperature accumulation below 1000 dºC. Changes in frost parameters are also marked. Other climatic and non-climatic factors would have to be considered to predict land-use change. Preliminary analysis suggests that changes in other climatic elements (e.g. windiness or precipitation) will complement the effects of a temperature increase.