Geology Reference
In-Depth Information
most insidious pollutants today is carbon dioxide, which paradoxically is also an essen-
tial nutrient for plants, which they harvest from the atmosphere. But it is also a green-
house gas, and too much of it causes the climatic mayhem that leads to extinctions.
P
opulation:
This refers to the explosive growth in human numbers, especially since
the industrial revolution. The current world population stands at 6.4 billion, and is pro-
jected to level off at around 10 billion by 2150. People need land, water food and shel-
ter, and have to satisfy these needs by destroying wild nature. But it is not just a ques-
tion of sheer numbers, for the amount of resources consumed by each person is what
really makes a difference to our impact on the planet. Paul Erlich devised his famous
I=PAT equation (pronounced IPAT) to make this point. 'I' stands for impact; 'P' stands
for population, 'A' stands for affluence and 'T' stands for technology. Human impact is
a product of the last three terms, so that it is possible to have a high population so long as
people don't have much money to spend on industrial products. In the current economic
climate, all the terms on the right hand side of the equation are increasing alarmingly.
Today, the world's middle class number about 20% of the population, but they consume
about 80% of the available resources. An oft-quoted fact: if everyone in the world were
to consume as much as the average American, three to four extra planets would be re-
quired to provide the raw materials.
The huge pressures of the human population drive all the other causes of extinction,
including the last of them all, over-harvesting.
O
ver-harvesting:
About one third of endangered vertebrates are threatened in this
way. Often the over-harvesting is carried out by poor rural people left with no other
means of surviving after they have been forced off their lands by global economic
forces. The rich countries of the North are also responsible for over-harvesting, and are
especially responsible for driving several key fisheries to the point of extinction—the
Grand Banks and the North Sea cod fisheries are sad examples. Many of the world's
great whales—the right, the bowhead and the blue—had been pushed to the edge ex-
tinction by the early 20th century. Detailed mathematical models designed to calculate
'maximum sustainable yield' for some of these species were spectacular failures that
led to catastrophic declines. Illegal whaling has been blamed for this, but the difficulties
of observing and quantifying whale behaviour in the wild were also responsible. Many
whale species have been protected to some extent since 1946, and a few, like the minke
whale, are recovering, but many smaller cetaceans such as dolphins are killed every year
when they become entangled in the nets of the fleets that are decimating the world's
fisheries.
Vanishing Species
