Human Impact on the Biosphere

Chapter 45

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, per capita resource use is low but growing, as is population size

• In developed countries, population growth has slowed but per capita resource use is already high

Pollutants

• Substances which have harmful effects on

humans and the natural world

• Substances with which an ecosystem has had

no prior evolutionary experience

• No adaptive mechanisms are in place to deal

with them

Air Pollutants• Carbon oxides burning fossil fuel• Sulfur oxides mostly from coal• Nitrogen oxides mostly from cars• Volatile organic compounds =

unburned Hydocarbons• Photochemical oxidants = ozone • Suspended particles = smoke, soot

Industrial (Gray) 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

• Reddishbrown-air smog

• Forms when sunlight interacts with

components from automobile exhaust

• Nitrogen oxides are the main culprits

• Hot days contribute to formation

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/Acid Rain

• 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

• Lets in more UV radiation

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 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

• 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

• Sustainable? Not for much longer

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 = desertification

• Amplification of the greenhouse effect

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 usually by over

grazing

• Conversions of cropland that result in

more than 10 percent decline in

productivity

The Dust Bowl

• Occurred in the 1930s in the Great Plains

• Farming marginal land prolonged drought left the ground bare

• 1934 winds produced dust storms that stripped about 9 million acres of topsoil

Ongoing Desertification

• Sub-Sahar 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

Aquifer Problems

Water Pollutants

• Sewage containing organic wastes become Oxygen Demanding Wastes

• Fertilizers stimulate algal growth• 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

(ODW)

• 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 like wood)

Fossil Fuels

• Coal, oil, natural gas

• Main energy source of developed

countries

• Burning of fossil fuels contributes to

global warming, air pollution, & acid

rain

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

• Good news, there is a lot of it. Bad

news, we have to use it

• Mining is very destructive

• Burning coal releases sulfur dioxides

that cause acid deposition. Sulfur

can be removed (at a cost)

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 dangerous 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

Humans and Change

• Unlike previous species, human

have the capacity to observe and

make decisions about the changes

they bring about

• Hopefully we will in time!