Conclusions F 4.3 237 F 4.3 Conclusions For ecosystems, the anticipated climatic outcomes may either be catastrophic or mild, such is the wide range of known effects and so varied are the proven effects.As the final result of a structural change in the entire Earth System, small-scale and large-scale biotopes can in many instances be seen as the ‘victims’ of anthropogenic remote impacts (Graßl, 1999). In addition, they are subject to a whole host of direct human activities that cause long-term disruptions in the regulatory function they perform for the global Earth System (Chapter E, Section F 3). To that extent, viewing the atmospheric impact on any ecosystem type in isolation is a scientifically necessary task, but the experimental findings are all too fragmentary and uncertain (Chapter J). For a realistic assessment ofthe ‘behaviour’ ofthe biosphere in global transition we lack the work that will put the individual pieces ofthe puzzle back together.And so, in the view ofthe Council, incorporation of all interactions into a comprehensive, coherent explanatory approach to global climate-biosphere-interactions remains the challenge for the research community. More exact results with regard to the reaction of individual organisms, their population momentum andthe interaction between populations may be expected from a further development and combination of physiological and behavioural models (Orians, 1996). It is only via that route that in future effective prognostic theories on ecosystem reactions to climate change can be developed. In light ofthe diversity ofthe individual effects within an ecosystem, only a few generalized, global recommendations for action may be made. First of all, the steps under the Framework Convention on Climate Change have certainly not been implemented sufficiently in order to demonstrate any recognizable impact on ecosystems. For that reason effective implementation ofthe Kyoto Protocol remains an urgent imperative. Secondly, since all measures to reduce greenhouse emissions help in principle to maintain the functionality ofthe biosphere, the full spectrum of local and regional climate protection projects should receive unqualified support.
F 5 Critical elements ofthe biosphere in the Earth System F 5.1 Feedback mechanisms In the history ofthe Earth there has never been a completely stable biosphere. Gradual changes in a seemingly unpredictable manner seem to have been succeeded by erratic and sometimes disastrous upheavals (Crowley, 1996). Cosmic disasters alone, such as meteors hitting the Earth, cannot explain these completely. Apart from the Milankovic Cycles (eg Broecker and Denton, 1990) which explain the majority ofthe semi-periodically occurring Ice Ages, the variability of solar irradiation may possibly actually play a relatively minor role. Although in the course ofthe Earth’s history solar irradiation has increased by approx 30 per cent and demonstrates considerable variability in short timescales (Lean and Rind, 1996) the only similarities that have been found are those between the changes in the surface temperature ofthe seas andthe intensity fluctuation ofthe sun’s radiance. No such connection has been recognized between irradiation andthe temperatures on land (Schönwiese, 1992b; Nisbet, 1994). Even though these results certainly do not provide any definitive assessment ofthe role of external influences on the living conditions on Earth, they cannot explain the surprisingly sudden changes that are seen in the paleoclimatic data. Reconstruction of climate history by means of analysis of ice cores shows convincingly that climate activity often demonstrates abrupt changes.Within just a few years the temperature conditions seem to have changed completely although solar irradiation changed relatively slowly. The unmistakable message ofthe ice cores is that the climate is fragile, can change swiftly and drastically but also shows phases of high degrees of stability. The climate system therefore seems to have a ‘switch’ that is moved at certain very specific thresholds. This image should not be pushed too far however. Of course it is not a switch in the sense of a simple electrical circuit. It is even doubtful whether any single element in the Earth System demonstrates that sort of inconstant characteristic. This is true in particular ofthe biosphere. Non-linear systems theory provides appropriate explanations for the switch function: in its thermodynamic structure the Earth is a ‘semi-open non-equilibrium system’. It permanently receives energy from the sun that drives a number of processes within the Earth System. From direct warming ofthe Earth’s surface in accordance with the respective reflective capacity (albedo), absorption of long-wave thermal rays in the atmosphere, right through to balancing out thermal differences through transportation of heat there is a cascade of effects and processes. In this context, individual processes could demonstrate what is called a non-linear response behaviour. Minute changes in irradiation could have much greater impact for example on the hydrological cycle. If this were to be true generally, however, the climate system would be a great deal more unstable which, at least for the last 10,000 years, has not been the case. Therefore, the only explanation that remains is one of a systemic behaviour that results as a consequence of coupling various processes. And that sort of coupling usually involves the biosphere to a large extent. Process coupling can in principle only manifest itself in two forms: two or more processes can attenuate one another, which is termed negative feedback, in the form of a regular process that attenuates the stronger external influence, or they can amplify one another. This leads to a greater overall effect and is termed a positive feedback (Section F 3). As a result of an external (or internal) disruption the timing ofthe system in both feedback effects and can demonstrate unstable behaviour in the form of dramatic effects. F 5.1.1 Dramatic changes as marginal patterns of negative feedback effects Through negative feedback loops, systems can be constructed that respond in a stabilizing fashion within certain limits. As an example, let us take the