Geoscience Reference
In-Depth Information
Table 1.9 Energy systems, their duration, daily consumption (in kcal per capita) and yearly
consumption (in GJ per capita)
Energy systems
Duration (years)
Per capita energy
per day (kcal)
Per capita energy
per year (GJ)
7
×
10
6
Food
2,000
3
10
5
Fire
5
×
4,000
7
10
4
Agriculture
1
×
5,000
6,000
8
-
5
×
10
2
Fossil Fuels
37,000
56.5
Source see text. See also, with different results, the estimates by Cook (
1971
)
1.5 Conclusion
The long history of energy consumption until today can be thus summarized
(Table
1.9
)
22
:
the age when food was the only energy input extended over 5
7 million years
and energy consumption per day could average about 2,000 Cal (that is 3 GJ per
year);
-
the age of
re was the only carrier except food)
lasted some 1,000,000 years. Consumption can be established around
4,000
re (that is the epoch when
5,000 Cal per day or 6
8 GJ per year;
-
-
the age of agriculture lasted some 10,000 years and World daily energy con-
sumption per capita was about 5,000
6,000 Cal or 7
9 GJ per year;
-
-
the age of fossil fuels lasted about 500 years and will
nish this century or the
next. Daily World consumption has been around 37,000 Cal or 56.5 GJ per year
(according to a weighed average, based on population in the last two centuries).
The following data on energy consumption, although speculative, are not
implausible.
Calculations of the number of humans since the origins are naturally uncertain
and tentative depending on several assumptions; among which the epoch of the
beginning of our species is of particular importance. If we accept that the hypothesis
of 100 billion humans from 1 million years ago until today (an estimate proposed in
the 1990s), is low and that our species was born 7
10 million years ago (such as the
paleologists are nowadays inclined to believe), we must add at least 20
-
30 billion
people. If the amount of people ever born from the origins numbers some 120
-
-
130 billion, today 5 % of our species is alive, and 18 % of the total World
population has lived in the age of fossil fuels, beginning around 1600. This neg-
ligible part of the population, during the 0.01 % of time since the beginning of the
species, consumed about 80 % of the energy ever consumed by humans. If the more
recent period between 1700 and 2000 is observed, humans consumed 32 % of the
whole wealth in fossil fuels. Consumption of coal was negligible in the 18th century
-
22
Both on past and future energy consumption see the useful reconstruction by Beretta (
2007
).
