Chapter 23 Humans and the Environment The Biodiversity Crisis
A Global Connection
Convection cell- patterns of rising and falling air
Groups of convection cells form the system of global air circulation that helps determine climate
In the southern Pacific Ocean, the usual pattern of convection cells creates a wind that blows from east to west and pushes warm surface water from South America toward Australia.
Along the South American coast, cold water rises from deeper in the ocean and replaces the warm water.
This rising current is called an upwelling and it brings with it organic material and nutrients that support an abundance of plankton.
The plankton in turn supports an abundance of fish.
The Peruvian economy along with sea birds depends on normal atmospheric conditions.
But sometimes, usually in December, the normal east-to-west winds do not form over the Pacific Ocean.
Instead, winds push warm water eastwards toward the coast of South America.
When these conditions occur, the warm surface water cuts off the upwelling of nutrients.
The event is called El Nino.
Consequences of El Nino
The fish populations decline and Peruvian anchovy exports decrease because of the halted upwelling.
Fewer anchovies mean fewer birds and reduced guano population.
Peruvians need guano for fertilizer.
Northeastern Australia can suffer summer drought leading to reduced grain production there.
The southeastern United States gets higher rainfall in El Nino years, boosting agriculture while also decreasing forest fires.
Ozone is a naturally occurring gas in the upper atmosphere that is vital to life on Earth.
Ozone protects life from deadly ultraviolet rays.
Humans if exposed to UV light can suffer skin cancer and cataracts.
Several kinds of human-made chemicals are diminishing the ozone shield.
A major chemical that destroys the ozone is chlorofluorocarbons or CFC’s.
CFC’s are used in coolants in fridges, air conditioners and in aerosol cans.
Consequences of Ozone Depletion
Due to the ozone depletion, UV rays are negatively affected life on Earth.
Plants and algae are also damaged by UV rays.
The rise in skin cancer indicates the ozone layer is still thinning.
A global agreement has been reached that has cut CFC’s by 75%.
Hopefully, the ozone will recover within 50-100 years.
Increasing Carbon Dioxide
Carbon dioxide or CO 2 , is a naturally occurring gas that is the raw material of photosynthesis and a byproduct of respiration.
It is released when fossil fuels are burned.
This includes, natural gas, coal and petroleum.
Around the middle of the 19 th century, humans began to use fossil fuels more frequently.
Carbon dioxide levels and global temperatures have risen as a result of the increased use of fossil fuels.
Effects of Rising CO 2 Levels
There is a correlation or cause and effect relationship exists between global temperatures and carbon dioxide levels.
As carbon dioxide levels increase due to increased use of fossil fuels, global temperatures will rise causing drastic changes to our environment.
Future Population Growth
The human population is currently just above 6 billion and growing at a rate of about 90 million per year.
The United Nations estimates that by the year 2050 the world’s population could be more than double.
How would the doubling of the human population affect the environment?
The Biodiversity Crisis
Biodiversity- the variety of organisms in a given area; can be measured different ways
Evenness- the number of individuals belonging to particular species
Genetic diversity- amount of genetic variation
Genetic diversity is an important measure of biodiversity
Species richness is the number of different types of species.
Measuring Earth’s Biodiversity
Biologists estimate that there are at least 10 million species on Earth and possibly as much as 30 million.
Mammals are actually a small portion of the Earth’s biodiversity.
Most species are insects, plants and crustaceans.
Biologists estimate that up to 20% of existing species may become extinct by the year 2030.
There have been 5 major extinctions in the past and the 6 th is currently happening.
The 6 th extinction is different in that it is being caused by humans instead of natural causes.
The greatest threat to biodiversity is destruction of habitats.
Since the discovery of agriculture 10,000 years ago, more than ½ of the world’s tropical rainforests have been destroyed.
Rainforests contain the most biodiversity so their destruction is especially damaging to the world.
Ways to Save Biodiversity
Many countries that have tropical rainforests are some of the economically poorest nations on Earth.
In a process called debt-for-nature swap, richer countries or private conservation organizations pay off some of the debts of a developing country in exchange for the country to protect their biodiversity.
This could be setting up a preserve, launching educational programs, or promoting ecotourism.
Importance of Biodiversity
Utilitarian value- thinking of economic benefits that biodiversity provides humans
Some species are valuable as sources of medicines.
Nonutilitarian value- life-forms have value simply because they exist apart from any human uses.
Many people have both reasons to preserve biodiversity.
Why is the upwelling on the coast of Peru important to that country?
Describe the consequences of El Nino?
How have CFC’s affected the atmosphere? How might this change affect humans?
Describe some possible effect of a continued increase in the human population.