The tolerable windows approach: Theoretical and methodological foundations

The tolerable windows (TW) approach is presented as a novel scheme for integrated assessment of climate change. The TW approach is based on the specification of a set of guardrails for climate evolution which refer to various climate-related attributes. These constraints, which define what we call tolerable windows, can be purely systemic in nature - like critical thresholds for the North Atlantic Deep Water formation - or of a normative type - like minimum standards for per-capita food production worldwide. Starting from this catalogue of knock-out criteria and using appropriate modeling techniques, those policy strategies which are compatible with all the constraints specified are sought to be identified. In addition to the discussion of the basic elements and the general theory of the TW approach, a modeling exercise is carried out, based on simple models and assumptions adopted from the German Advisory Council on Global Change (WBGU). The analysis shows that if the global mean temperature is restricted to 2 degrees C beyond the preindustrial level, the cumulative emissions of CO2 are asymptotically limited to about 1550 Gt C. Yet the temporal distribution of these emissions is also determined by the climate and socio-economic constraints: using, for example, a maximal tolerable rate of temperature change of 0.2 degrees C/ dec and a smoothly varying emissions profile, we obtain the maximal cumulative emissions, amounting to 370 Gt C in 2050 and 585 Gt C in 2100

The potential role of spectral properties in detecting thresholds in the Earth system: application to the thermohaline circulation

\enspaceA simple two-box model of the hemispheric thermohaline circulation (THC) is considered. The model parameterizes fluctuations in the freshwater forcing by a stochastic process. The dependence of the power spectral density and the lifetime of quasistationary states of the THC on the distance to the bifurcation point, where the THC collapses, is calculated analytically. It is shown that power spectral properties change as the system is moved closer to the bifurcation point. These changes allow an estimate of the distance to the bifurcation point

The Syndromes Approach to Scaling: Describing Global Change on an Intermediate Functional Scale

A dynamic description of Global Change on an intermediate functional scale on the basis of approximately independent sub-models is elaborated. Sixteen of these sub-models are primarily identified as Hazardous Functional Patterns (HFPs) generating nonsustainable trajectories (Syndromes) of the civilisation/nature system. After an ‘‘idealistic deduction’’ of the main concepts an iterative procedure – formally based on Qualitative Differential Equations – is introduced which allows the systematic generalisation of case study based knowledge to obtain consistent HFPs on a coarser functional scale. The method is illustrated with the Sahel HFP

Optimization of global CO2 emission based on a simple model of the carbon cycle

A simple model has been designed to describe the interaction of climate and biosphere. Carbon dioxide, understood as a major emitted gas, leads to a change of global climate. Economic interpretation of the model is based on the maximisation of the global CO2 cumulative emissions. The two most important profiles of emission have been obtained: optimal and multi-exponential suboptimal profiles, each displaying different characteristics