Human Impact on the Biosphere

Intro to Environmental Science

Human Impacts

• Humans are using energy and altering

the environment at astonishing rates

• We are altering natural processes

before we even understand them

Developing vs. Developed

• In developing countries (LDCs), per

capita resource use is fairly low but

growing, as is population size

• In developed countries (MDCs),

population growth has slowed but per

capita resource use is very high

Pollutants

• Substances with which an ecosystem

has had no prior evolutionary

experience or adaptive mechanisms.

• Depends on concentration, location,

and timing.

Air Pollutants

• Carbon oxides

• Sulfur oxides

• Nitrogen oxides

• Volatile organic

compounds(VOCs)

• Photochemical oxidants

• Suspended particles

Industrial Smog

• Gray-air smog

• Forms over cities that burn large

amounts of coal and heavy fuel oils;

mainly in developing countries

• Main components are sulfur oxides and

suspended particles

Photochemical smog

• Brown-air to orange smog

• Forms when sunlight interacts with primary

release chemicals

• Nitrogen oxides are major culprits

• Hot days contribute to formation as does

thermal inversion

Thermal Inversion

• Weather pattern in which a layer of cool, dense air is trapped beneath a layer of warm air

cool air

warm inversion air

cool air

Acid Deposition

• Caused by the

release of sulfur and

nitrogen oxides

• Coal-burning power

plants and motor

vehicles are major

sources

Ozone Thinning

• In early spring and

summer ozone

layer over

Antarctica thins

• Seasonal loss of

ozone is at highest

level ever recorded

SouthAmerica

Antarctica

Effect of Ozone Thinning

• Increased amount of UV radiation

reaches Earth’s surface

• UV damages DNA and negatively

affects human health

• UV also affects plants, lowers

primary productivity

Protecting the Ozone Layer

• CFC production has been halted in

developed countries, will be phased out

in developing countries

• Methyl bromide will be phased out

• Even with bans it will take more than 50

years for ozone levels to fully recover

Generating Garbage

• Developed countries generate huge

amounts of waste

• Paper products account for half the

total volume

• Recycling can reduce pollutants, save

energy, ease pressure on landfills

Land Use

• Almost 21 percent of Earth’s land is used

for agriculture or grazing

• About half the Earth’s land is unsuitable

for such uses (non-arable)

• Remainder could be used, but at a high

ecological cost

Green Revolutions

• Improvements in crop production

• Introduction of mechanized agriculture

and practices requires inputs of

pesticides, fertilizer, fossil fuel

• Improving genetic character of crop

plants can also improve yields

Deforestation

• Removal of all trees from large tracts

of land

• 38 million acres logged each year

• Wood is used for fuel, lumber

• Land is cleared for grazing or crops

Effects of Deforestation

• Increased leaching and soil erosion

• Increased flooding and

sedimentation of downstream rivers

• Regional precipitation declines

• Possible amplification of the

greenhouse effect

Regions of Deforestation

• Rates of forest loss are greatest in

Brazil, Indonesia, Mexico, and Columbia

• Highly mechanized logging is

proceeding in temperate forests of the

United States and Canada

Reversing Deforestation

• Coalition of groups dedicated to saving

Brazil’s remaining forests

• Smokeless wood stoves have saved

firewood in India

• Kenyan women have planted millions of

trees

Destroying Biodiversity

• Tropical rainforests have the greatest

variety of insects, most bird species

• Some tropical forest species may prove

valuable to humans

• Our primate ancestors evolved in forests

like the ones we are destroying

Desertification

• Conversion of large tracts of grassland

to desertlike conditions

• Conversions of cropland that result in

more than 10 percent decline in

productivity

The Dust Bowl

• Occurred in the 1930s in the Great Plains

• Inappropriate cultivation techniques,

overgrazing and prolonged drought left the

ground bare

• 1934 winds produced dust storms that

stripped about 9 million acres of topsoil

Ongoing Desertification

• Sahel region of Africa is undergoing

rapid desertification

• Causes are overgrazing, overfarming,

and prolonged drought

• One solution may be to substitute native

herbivores for imported cattle

Water Use and Scarcity

• Most of Earth’s water is too salty for

human consumption

• Desalinization is expensive and

requires large energy inputs

• Irrigation of crops is the main use of

freshwater

Negative Effects of Irrigation

• Salinization, mineral buildup in soil

• Elevation of the water table and

waterlogging

• Depletion of aquifers

Ogallala Aquifer

• Extends from southern South Dakota to

central Texas

• Major source of water for drinking and

irrigation

• Overdrafts have depleted half the water

from this nonrenewable source

Aquifer Problems

Water Pollutants

• Sewage

• Animal wastes

• Fertilizers

• Pesticides

• Industrial chemicals

• Radioactive material

• Excess heat (thermal pollution)

Wastewater Treatment

• Primary treatment – Use of screens and settling tanks

– Addition of chlorine to kill pathogens

• Secondary treatment – Microbes break down organic matter

• Tertiary treatment removes additional toxic substances; rarely used

Water Wars?

• Per capita amount of freshwater

available is decreasing

• International conflicts over water use

and quality have already occurred

• Building dams or dumping pollutants

effect countries downstream

Energy Use

• Only 10 percent of energy used in

developed countries is from

renewable sources

• Less developed countries rely more

heavily on renewable sources

(primary biomass)

Fossil Fuels

• Coal, oil, natural gas

• Main energy source of developed

countries

• Burning of fossil fuels contributes to

global warming

Oil

• Reserves are declining

• Many reserves are in ecologically fragile

wilderness areas

• Environmental costs of extracting and

transporting reserves from such areas

are high

Coal

• Extensive reserves exist

• Mining is very destructive

• Burning coal releases sulfur dioxides

that cause acid deposition

Nuclear Energy

• Used extensively in some energy-poor developed countries

• Little support in the United States

• Emits fewer air pollutants than burning coal, but creates radioactive wastes

• Potential for meltdown

Chernobyl Accident - 1986

• Core meltdown at a nuclear power plant in the Ukraine

• 31 immediate deaths, radiation sickness and death for others

• Cloud of radiation spread by winds across Europe

• Long-term health impacts downwind

Solar-Hydrogen Energy

• Photovoltaic cells use sunlight

energy to split water

• Hydrogen gas produced in this way

can be used as fuel or to generate

electricity

• Clean, renewable technology

Wind Energy

• An indirect use of solar energy

• Wind farms are arrays of turbines

• Can supplement needs of some

regions but is not dependable

enough on it own

Fusion

• Energy is released when atomic nuclei fuse

• This process produces solar energy

• Attempts to mimic this process on Earth require use of lasers, magnetic fields

• Not yet a commercially viable energy source

Changes in the World of Life

• Adaptations of species have

changed the environment

• Photosynthetic organisms that

arose during the Proterozoic altered

the atmosphere by adding oxygen

• Change is natural

Humans and Change

Unlike previous species, human

have the capacity to observe and

make decisions about the changes

they bring about

The Big Picture

Environment

Socio-politics Economics

References

• Modified from presentation of Prentice Hall Publishers, 2002