The concentration of CO2 in the atmosphere has been steadily increasing since the onset of the industrial revolution (Houghton et al. 1990; Keeling et al. 1989). General circulation models (GCMs) of the earth's climatic system predict that the continued increase in the atmospheric concentrations of CO2 and other greenhouse gases will cause climatic warming (Houghton et al. 1990, 1992; Wigley & Raper 1992). This is a clear and neat solution. However, the global climate system is neither as neat nor as simple. The changes in global temperatures over the last 40 years do not closely mirror the changes in C02, so clearly the greenhouse effect of increased CO2 is not a simple relationship. The Intergovernmental Panel on Climate Change (IPCC) has investigated some of the atmospheric and terrestrial processes which influence the climate system (Houghton et al. 1990, 1992). Wigley & Raper (1992) describe how future climate can be influenced by a range of factors including changes in policies on greenhouse gas emissions, the influences of SO2 and sulphate aerosol production, cloud formation, uncertainties in the global carbon cycle and the negative feedback on halocarbon effects through the depletion of stratospheric ozone. New information on all of these influences leads to current model projections of global warming for the year 2050, which are about 1 ?C less than the 1990 report of the IPCC (Houghton et al. 1990). The model projections are still likely to be in error because the degree of the feedback between terrestrial and oceanic ecosystems and climate, through changes in the fluxes of CO2 and water vapour, is still unknown (Wigley & Raper 1992). The nature and degree of feedbacks between climate and parts of the climate system are major limitations to adequate predictions of future climate. Taking account of the new projections of climatic change (Wigley & Raper 1992) and the modelling of Climate Change Impact Review Group (CCIRG) (1991), then it is possible to suggest the following changes in UK temperatures by the year 2050: Summer Temperature + 1.1 ?C, uniformly over UK Winter Temperature + 1.7?C, northern limit of UK + 1.2?C, southern limit of UK (linear south/north gradient). GCM predictions of future precipitation are notoriously unreliable (Schneider 1992). However, CCIRG (1991) suggests that the summer precipitation is most likely to remain unchanged, while the winter totals may increase by about 4%. A future problem will be that the basically physical portrayal of the climate system will, increasingly, incorporate feedbacks which are under human control, e.g. C02, CH4, NO, and CFC emissions. Therefore the climate model will be more like an economic model (The Economist 1992) in which predictions from the model can lead to changes in climate, through changes in policy on emissions. If the economic analogy is carried on then it is likely that the fundamental uncertainties which characterise economic models may then spread to climate models, suggesting a decreased potential for adequate future predictions of climate. In spite of this consideration, it is important to consider the prospects for climatic change and for the probable influence of these changes on the biosphere. Just as there is a human effect on climate there is also a human effect on conservation of natural, living resources. If we are convinced of likely changes in climate then there must be argument and discussion about management responses to these changes. Although it may prove impossible to prevent changes in vegetation, for example, it is possible that greater weight should be given to the conservation of species and this must be accommodated somewhere in the models. This argument strongly favours the conservation and maintenance of diversity, in this case as an end in itself, and international bodies such as IGBP (1992), WCMC (1992) and SCOPE (1990) are now actively pursuing the importance of diversity to the continued functioning of ecosystems and their responses to environmental change. There are many aspects of the responses of British vegetation to global change which might be used to forecast changes in their ecology. In this paper we illustrate some effects of future climatic warming on the British landscape by reference to native and introduced species. Special emphasis is placed on the native pine forests of Scotland and two introduced and aggressively invasive species Fallopia japonica and Impatiens glandulifera. In the next 100 years the responses shown by pine forests to the climatic amelioration of the late-glacial (Dubois & Ferguson 1985) may be repeated as global change takes place, but this time the response may be to conditions which have not been previously experienced for at least the last 200 000 years (Houghton et al. 1990). For native pine 391
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Dec 1, 1994
Robert L Wilby 
Open Access