Causes of the greenhouse effect

Objectives today:

1. Explain that energy can enter and leave an ecosystem, but that nutrients must be recycled

2. Recall process of the carbon cycle (to include photosynthesis, respiration, fossilization and combustion)

3. Describe the greenhouse effect

4. Explain what is meant by “enhanced greenhouse effect”

5. Give evidence for greenhouse effect

CARBON CYCLE

The Carbon Cycle:

• The amount of carbon on Earth is fixed.

• Minerals are constantly cycled one of the most important is carbon.

• 16 000 000 000 tonnes of carbon are cycled through the living world each year!

Video summary of Carbon Cycle

http://www.youtube.com/watch?v=0Vwa6qtEih8

Carbon cycle diagram

Key processes• Respiration• Photosynthesis• Combustion• Decay• Fossilisation• Ocean + Atmospheric gas exchange• Weathering

Feeding

CO2 in atmosphere and oceans

COW

Photosynthesis

Combustion

Respiration

Death

Excretion

Decomposers

Formation of Fossil Fuels

● Amount of atmospheric CO2 depends on the balance between carbon fixation during photosynthesis and the release of CO2 from respiration, combustion and decay by micro-organisms.

● Why do we see daily fluctuations in CO2 levels?

In the cycling of carbon in nature state in what forms inorganic carbon can exist in the:

● The atmosphere

● The lithosphere

● The hydrosphere

Q- How does digging up and burning fossil fuels affect the carbon cycle?

Q – How does cutting down rainforest to create cattle farms affect the carbon cycle?

The amount of Carbon on Earth is fixed. The proportion at any stage of the cycle depends on the balance of processes.

The Greenhouse Effect

The Greenhouse effect

● Greenhouse gases absorb and re-emit IR radiation.

Examples include:– CO2

– Methane CH4

– Water vapour

– Pollutants such as NOx and CFC also have greenhouse properties

The greenhouse effect is a natural process

High frequency IR from sun

Earth radiates in lower frequency IR

Earth

The Green House Effect

atmosphere

Mars Earth Venus

T/ºC

-57-47

-46

+ 477

-18+15

Size of greenhouse effects

The composition of the atmosphere changes over time

The concentration of greenhouse gases naturally fluctuates

Evidence : Ice core samples • Composition of gas bubbles = greenhouse concentration • Oxygen isotopes = temperature• Data for last 400 thousand years (Vostok)

Close correlation between temperature an greenhouse gas levels (evidence for greenhouse effect)

•Decline of both greenhouse gases and temp in glacial periods•Rapid rises of both in deglaciation•Climate has been relatively warm and stable last 10 thousand years.

The “enhanced greenhouse effect”

Since industrialisation the amount of CO2 in the atmosphere has increased dramatically. Monitored on Mauna Low since 1957 Seasonal fluctuations in CO2 Trend of annual increase

Levels of CO2 have fluctuated over the last 20,000 years it is the past 200 years that levels have been high and consistently rising.

• Previously rises due to weathering of chalk and limestone and volcanic activity. Today volcanoes contribute only 1% - what is main contributor now?

Does the rise in atmospheric CO2 correlate to temperature data?(fig 5+6 p179)

Its going to happen!

What scientist are debating is:

• By how much• How long will it take• What will the effects be

Questions:

1. What is the % change in mean atmospheric carbon dioxide between 1960 and 2000?

2. What processes have lead to the recent rise in atmospheric CO2?

3. Why is there seasonal variation in CO2 levels?

4. In which regions would you expect seasonal variation to be most pronounced? Why?

The precautionary principle:

• Better safe than sorry• No official definition it is when:

When an activity raises threats of harm, measures should be taken, even if a cause-and-effect relationship has not been established scientifically

Principle is used as justification for strong action to tackle threats posed by enhanced global warming:

To implement need to know the likely consequences and actions that may combat threats.

Energy from Sun

Energy lost to space

Balance when T is constant

BUT some molecules in the troposphere have polar bonds. These absorb photons of IR radiation whose energy corresponds to the gap between the vibrational energy levels of the molecule.

This increases the vibrational energy of the molecule and so increases the temperature of the stratosphere as the energy is passed on to other molecules when they collide.

Energy from Sun

Energy lost to space

With less energy lost to space there is now a net gain of energy by the earth – until a new balance is reached at a higher temperature.

Atmospheric Co2 ppm vol. source: Australian government

Atmospheric co2 concentration and global change in average temperature since 1880Source: NASA