Greenhouse EffectTopic 5.2

The Carbon Cycle

The Carbon CyclePhotosynthesis takes CO2 out of the atmosphere

Cell Respiration by all organisms puts CO2 into the atmosphere

Transfer of carbon through food chainsUptake of CO2 by bodies of water and trapped as

limestone or in organisms shells. Fossilization - carbon becomes trapped in sediment

as coal, oil, and gasCombustion through the burning of fossil fuels and

trees

Changes in Atmospheric Carbon Dioxide Levels

The Greenhouse Effect

A natural phenomenon necessary for sustaining life by keeping temperature at a level where metabolic processes can occur.

How it worksEnergy in the form of solar radiation is

emitted toward earth. 26% is reflected, 19% absorbed, 55% reaches

earth’s surface. 4% of that is reflected to space and the remaining 51% is absorbed by earth’s surface and re-emitted as long wave infrared radiation.

In a greenhouse, light penetrates the glass – incoming short-wave radiation

Light energy is converted to heat energy and is re-radiated – outgoing long-wave infrared radiation causing the greenhouse to warm up.

The heat is trapped and warms the atmosphere

The atmosphere around the Earth acts like a giant greenhouse.

Selected Greenhouse Gases• Carbon Dioxide (CO2)

– Source: Fossil fuel burning, deforestation Anthropogenic increase: 30% Average atmospheric residence time: 500 years

Methane (CH4) – Source: Rice cultivation, cattle & sheep ranching, decay

from landfills, mining Anthropogenic increase: 145% Average atmospheric residence time: 7-10 years

Nitrous oxide (N2O) – Source: Industry and agriculture (fertilizers) Anthropogenic increase: 15% Average atmospheric residence time: 140-190 years

Summary

Greenhouse gases absorb infrared radiation and prevent it from escaping to space.

Carbon dioxide, methane, and nitrous oxide are very good at capturing energy at wavelengths that other compounds miss

Greenhouse Effect & Global Warming• The “greenhouse effect” & global

warming are not the same thing. – Global warming refers to a rise in the temperature

of the surface of the earth

• An increase in the concentration of greenhouse gases leads to an increase in the the magnitude of the greenhouse effect. (Called enhanced greenhouse effect) – This results in global warming

Montreal ProtocolWas called in 1987 because of health

concerns and fears of global warming.Signed by 180 nations, demanded CFC

production dropped by 50%. Several amendments now have dropped it to 95%.

Future of the ClimateScientists all agree earth’s climate is

warming due to increased greenhouse gas concentrations. They do not know how it will continue, however.

Some believe it will all work itself out.World Health Organization says immediate

and long term health benefits will come from reducing gas emissions.

Reducing Greenhouse GasesWe can build more efficient machines.

Automobiles are highly inefficient and transportation is second highest contributor to gas emissions in U.S.

Planting trees. An average tree intakes 13 pounds of carbon and carbon dioxide a year and maintains it for the life of the tree.

Consequence on Arctic Ecosystems

Consequence on Arctic Ecosystems

Increase of decomposition rates, therefore increase in heat and CO2 released

Decrease in permafrostDetritus previously trapped in permafrost now decomposing

Consequence on Arctic EcosystemsIncreased melting and loss of ice habitat –

great implication in arctic food chains, especially the polar bear.

decreased ice less algae effects entire food chain;

Polar bears hunt on ice. If there is less ice, there is less hunting

Increased expansion in range of habitats of temperate species (mosquitos where there were previous none; larger plants in the Tundra, instead of only mosses and lichens)

Increased success of pest species

Is it really getting warmer

1979 2003

© NASA

Precautionary Principle“If the effects of a human induced change would be

very large, or catastrophic, those responsible for the change must prove it will not do harm before proceeding”

Opposite to the “Burden of Proof” theory which states that those who are concerned about the impact have to prove it will do harm in order to prevent it.

The idea is that it is easier to prevent a problem now than try to fix it later.

This is particularly important when there is no scientific consensus on the outcome of the action

Examples: Addressing crime, GMO’s, Approval of Drugs, Climate Change

Everyday usage: "an ounce of prevention is worth a pound of cure", "better safe than sorry", and "look before you leap"

Considerations with respect to the greenhouse effect and global warmingRequires international cooperationInequality occurs between those contributing most to the

problem versus those who will be most harmed. Often those who suffer the consequences are not the ones creating the problem.

Economic impacts for a “maybe” versus the greater harm for future generations. Should farmers pay for technology that “may” help, even though there is no evidence that they are contributing to the problem)

Issues arise of when to apply the principle, where, and to what extent.

What are the consequences if some countries do and some countries don’t?

If the precautionary principle is not applied, by the time the effects are noticed, it would be too late to do anything about it.

The principle is similar to medicine, where it is preferable to prevent disease rather than wait for someone to get sick.