Climate change - the evidence so far and predictions for tree growth.

Abstract

Atmospheric carbon dioxide concentrations will continue to rise for the foreseeable future at a rate dependent on human activity and the success of the emission control policies prescribed at the United Nations Convention on Climate Change. Evidence suggests that this and other 'greenhouse' gases have already influenced our climate and may have had an effect on forest productivity during the course of the twentieth century. Predictions of future climate are now available, and the influence of climate change on forest growth can already be modelled through an analysis of spatial clines in climatic variables such as temperature and rainfall. The direct effects of atmospheric carbon dioxide concentrations and interactions with a changing climate are, however, more difficult to model. For these purposes, physiological or process-based models are required, in which the response of individual physiological processes to changing carbon dioxide concentrations is determined in controlled environment facilities and then parameterised for input into the growth models. The individual processes of these models can be validated by comparison with whole canopy water vapour and carbon dioxide flux data, while the growth predictions can be partially validated using historic climate and yield data. Only when these models are finalised and validated can we reliably predict the impact of climate change on forest growth.