World Human Population Energy Food Demand and Energy Consumption

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It is natural that the intensity of anthropogenic impact on the ecosphere depends (not usually in a linear way) on the size of human population, which grows as shown in Figure 2.

Two thousand years ago, there were a quarter of a billion people living on the planet. This had doubled to about half a billion by the sixteenth to seventeenth centuries. The next doubling required two centuries (from the middle of the seventeenth century to 1800), the following doubling occurred over only 100 years, while the last one took only 39 years.

Homo sapiens belongs to both the biosphere and anthropo-sphere. If we consider humans as animals, then all human energy requirements are satisfied through food, and the annual energy food demand per individual is 4 x 109J. Thus, in the year 2000, the annual energy food demand that determines the annual trophic flow to species H. sapiens in the world ecosystem must be 2.4 x 109J.

species with biomass 4.2 x 1014g (in the year 2000), constituting 2.8% of the total biomass of animals. Therefore, humans can use only 2.8 x 3 = 0.084% of the NPP, that is, 2 x 1018J. Thus, the food demand of mankind is more by almost 1 order of magnitude than the trophic flow, that is, the trophic chains including H. sapiens are very strained. It may bring in turn either global starvation or destruction of this chain, elimination of many species from the chain (or its elimination in the whole from the global ecosystem).

In 1650, human population was approximately 600 million, that is, an order of magnitude less than today (Figure 2). From this, it follows that that the trophic flow was equal to food demand, and the corresponding trophic chain was not strained. In other words, humans were still one of many species, coexisting within the biosphere.

On the other hand, if we consider the fate of H. sapiens from the point of view of physical theory of fluctuations, the probability of fluctuation, which could cause the elimination of H. sapiens, is equal to

Pr = exp energy demand for human population energy supply for all animals

At the time of the Neolithic revolution, the human population consisted of around 4 x 106 individuals, and required an energy supply of 1.6:

The Earth receives 3.5 x 1024J of solar energy Pr = exp[-1.6 x 1016/7.35

annually, providing the work of the 'green cover' with net primary production (NPP) equal to 5.5 x 1021Jyr_1 of new biomass. This energy flow also provides a steady state for 1.84 x 10 g of living biomass (or 3.5 x 1022J), and animal biomass constitutes only 0.8% of it, that is, 1.46 x 1016g. Animals consume only 3% of the NPP (7.35 x 1019Jyr~ ). Homo sapiens is one of the animal estimate this probability for the year 2000, then

If we we get

72.2%. Looking at these numbers one can say that H. sapiens as a biological species was very fortunate that it has not been eliminated before the anthroposphere arose. Namely, the industrial and accompanying agricultural revolution could mask the consequences of growing strain in the trophic chain.

8000 BC

7000 BC

6000 BC

5000 4000 3000 BC BC BC

2000 BC

1000 BC

1000 AD

2000 AD

Figure 2 Dynamics of the world population. From Heinke GW (1997) The challenge of urban growth and sustainable development for Asian cities in the 21st century. AMBIO 8: 130-143.

2-5 Million years

8000 BC

7000 BC

6000 BC

5000 4000 3000 BC BC BC

2000 BC

1000 BC

1000 AD

2000 AD

Figure 2 Dynamics of the world population. From Heinke GW (1997) The challenge of urban growth and sustainable development for Asian cities in the 21st century. AMBIO 8: 130-143.

Figure 3 Accelerating rate of use of fossil fuels and nuclear energy.

Year

Figure 3 Accelerating rate of use of fossil fuels and nuclear energy.

One of the main characteristics of the anthroposhere is the use of fossil fuels (traces of the past biospheres), and (at present) such 'nonbiosphere' energy as nuclear, with an accelerating rate (see Figure 3).

At the present time, the anthroposphere spends about 3 x 1020Jyr_1 to provide for its functioning. This is mainly energy of fossil fuels and nuclear energy (fraction of the 'pure' biosphere energy - hydropower station and firewood - in this balance is ~5%), and it constitutes about 13% of the global NPP, 2.3 x 1021Jyr~\ Nevertheless, this percentage is enough for the biosphere and anthroposphere to strongly compete for common resources, such as land area and freshwater. Contamination of the environment and reduction of biotic diversity are typical consequences of the competition.

Since the biosphere (considered as an open thermodynamic system) is at a dynamic equilibrium, all entropy flows have to be balanced as well. Therefore, the entropy excess, which is created by the anthroposphere, has to be compensated by means of two processes: (1) degradation of the biosphere, and (2) changes in the work of the Earth's climate machine (in particular, through increases in the Earth's average temperature).

The energy of dissipation, corresponding to the full destruction of biota (equivalent to its complete combustion), is equal to 3.5 x 10 J, while the energy dissipated by the anthroposphere is 3 x 1020J. Even if the rate of the energy consumption in the anthroposphere does not increase, then this 'anti-entropy storage' of biota can make up for the entropy, produced by the anthropo-sphere, in the next 120 years. If this 'technogeneric'

entropy could be compensated by soil destruction, then the agony would continue in the course of 300-400 years, since the storage of organic matter in soil is three- to fourfold larger than in biota.

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