Overshooting

It is difficult to predict the outcome of current changes. Exponential growth of some components (such as world population) or some factors (temperature of the oceans, level of CO2) indicates the direction of change, but cannot provide sufficient information to allow us to guess the future of the Gaia system. The Earth is an extremely complex environment, and growth curves are crude instruments for understanding it. In reality, we do not know where or when “overshooting” of limits will take place. At best, these tools give us a slight indication of the risk.

We must remember that natural processes never follow a linear or exponential path indefinitely. Once they reach a ceiling, a change takes place, and new relationships are established. Sometimes factors that are overlooked may be increasing or decreasing exponentially, and their effects may be felt suddenly. The greenhouse effect produces an increase in temperature, which in turn increases evaporation; this leads to increased cloudiness and an increase in the albedo of the planet, reducing radiation and decreasing temperature. Even a relatively simple model like this can be difficult to quantify, however, mainly because the data and relationships are poorly understood. For example, if we introduce the role of algae and photosynthesis in the upper layer of the oceans or the effect of ice melting at the poles, the situation becomes more complex. A model of the planet requires understanding and measuring thousands of variables, some of which are biological or anthropogenic in nature.

Although much can be done toward solving the riddle of our environmental future, we must remain cautious about forecasts. Because so little is known and the risk is so great, survival strategies must rely on the best interpretation of existing data. We may, in the end, “go beyond the limits inadvertently” because of inattention, inadequate information, a slow response, or simply the momentum (Meadows et al. 1992). On this “spaceship Earth,” however, we cannot afford to risk overshooting the limits, whatever they may be; we may not have a second chance.