Human activity as a thermodynamic process

In the last chapter before the summary, we extend the thermodynamic description to human activity to formulate the last link represented in Fig. 1.5. This application of thermodynamics to human activity is rather important, as human activity increasingly shapes the functioning of the Earth system. As we will see in this chapter, thermodynamics can provide a generalized view of human activity, its limits as well as its impacts within the Earth system.

The impacts of human activity are noticeable at the planetary scale and are reflected in, for instance, the increase in atmospheric greenhouse gases such as CO2 resulting in global climate change, stratospheric ozone depletion, the expansion of croplands and pastures, with about 40% of the land surface being placed under human use (Foley et al. 2005), and the alterations of the global cycles of nitrogen and phosphorus. The impact of human activity has reached such an extent that it has been suggested that the present day can be referred to as the new geologic era of the “Anthropocene” (Crutzen 2002). As the size of the human population as well as its energy consumption is likely to grow in the future, the effects of human activity on the Earth system are likely to increase as well. A description of the thermodynamics of the Earth system would be incomplete without a characterization of human activity and its effect on the Earth system.

Yet, the human role is often described as if it were separate from the functioning of the Earth system. There are certain aspects that are taken from the Earth to sustain human activity, such as food production or fossil fuels, as shown in Fig. 11.1a. Human activity then has impacts on the Earth system, for instance, in terms of land cover changes associated with food production, or global climate change due to the emission of CO2 resulting from the combustion of fossil fuels. The purpose of this chapter is to describe human activity as a dissipative process that is embedded within the functioning of the Earth system, just as it was done for the other processes in the previous chapters.