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Thematic Guide to Integrated Assessment Modeling
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Ecological Impacts
Ecosystem responses to changed climate and accompanying changes in trace-gas concentrations (particularly CO2) can be of two kinds. Existing plants can change their functioning, and the spatial distribution of species can shift. Ecological research is under way now to increase understanding of both these phenomena.A traditional representation of the relationship between ecosystem types and climatic zones is that of Holdridge Zones, which express the broadly observed empirical correlation of certain vegetation types with certain conditions of temperature and precipitation. This zone system is now widely regarded as inadequate, both because it lacks a process-based explanation and because it is static.
Two recent projects seek physiological, process-based explanations of the problem of vegetation types and climate. Melillo et al. (1993) address the question of how changed climate and CO2 concentration will change the productivity and nutrient cycling of specific types of plants, without examining shifts in their spatial distribution. Prentice et al. (1992) use physiological models to predict which plant types will occur and which will be dominant under particular climatic conditions. Their model predicts the distribution of plant types under present climate and produces better agreement with the observed distribution than do traditional methods. Their method is clearly also applicable to predicting the movement of ecosystem types under climate change, but such analysis has not yet been presented.
Teams from various climate integrated assessment projects are working with both these approaches to attempt to represent climate change effects on unmanaged ecosystems, but this work is at an early stage. This is clearly one of the most difficult components of climate integrated assessment and one that will require further advances in disciplinary knowledge for a thorough understanding.
The next section is Socioeconomic Impacts.
