Integrating Homo sapiens into ecological models: Imperatives of climate change

Emergy unsustainability index for agricultural systems assessment: A proposal based on the laws of thermodynamics

The anthropic effects of agriculture call for more sustainable systems. Agricultural sustainability conventionally communicates an idea of perennity. However, the sustainability of living open systems, like agricultural systems, can be regarded as a mere utopian idea when the effects of the laws of thermodynamics are taken into account. Under such physical laws, what really exists is the fact that any system alone has the property of unsustainability. The rate of entropy production can denote the potential level of the unsustainability of a system. The higher the rate of entropy production in an agricultural system, the higher its potential for unsustainability. Directly measuring entropy in living open systems is unfeasible. Even so, such systems are subject to the laws of thermodynamics. Indirect measurements of entropy in living open systems can be assessed by approximation through an analysis of the energy flows of the system. We used emergy analysis to account for the energy flows and compare the unsustainability among agricultural systems. However, the indicators proposed by emergy analysts have been more aligned with the perspective of sustainability. To change this perspective, we propose an emergy unsustainability index applied in this paper specifically to agricultural systems (EUI_AS). EUI_AS is not a simple inversion of the ESI obtained by the ratio between the Emergy Yield Ratio (EYR) and the Environmental Loading Ratio (ELR). The use of renewable exergy stored from one production cycle to another is one of the peculiarities of long-term agricultural systems. Therefore, quantifying the renewable and non-renewable fractions of resources used is fundamental to the EUI_AS. A higher EUI_AS means that an agricultural system is more dependent on non-renewable economic resources than renewable resources, and, in general, environmental impacts are higher due to the use of non-renewable resources.

Mathematical Modelling of Plankton-Oxygen Dynamics Under the Climate Change

Ocean dynamics is known to have a strong effect on the global climate change and on the composition of the atmosphere. In particular, it is estimated that about 70% of the atmospheric oxygen is produced in the oceans due to the photosynthetic activity of phytoplankton. However, the rate of oxygen production depends on water temperature and hence can be affected by the global warming. In this paper, we address this issue theoretically by considering a model of a coupled plankton-oxygen dynamics where the rate of oxygen production slowly changes with time to account for the ocean warming. We show that a sustainable oxygen production is only possible in an intermediate range of the production rate. If, in the course of time, the oxygen production rate becomes too low or too high, the system's dynamics changes abruptly, resulting in the oxygen depletion and plankton extinction. Our results indicate that the depletion of atmospheric oxygen on global scale (which, if happens, obviously can kill most of life on Earth) is another possible catastrophic consequence of the global warming, a global ecological disaster that has been overlooked.