Feedback mechanisms and tipping points

What is a feedback mechanism?

• A change in one environmental factor that may cause other factors to change

What are negative feedback mechanisms?

• An environmental change that causes other changes which decrease the rate of initial change or level of its impact

• There are 2 examples

1) Increase in low level cloud

1) Increase in temperature

2) Increase in evaporation

3) Increase in condensation

4) Increase in low level cloud formation

5) Increase in albedo= more sunlight (shortwave radiation) reflected

6) Reduction in insolation

7) Reduction in temperature

2) Increase in photosynthesis

1) Increase in temperature

2) Increase in rate of photosynthesis

3) Increase in the volume of CO2 taken in by plants

4) Decrease in atmospheric CO2

5) Decrease in temperature

What are positive feedback mechanisms?

Environmental change causes other changes which increase the rate of the initial change or level of its impact and thus increases the fact of the original change

• This sequences increases temperature directly or increase concentration of GHGs which will cause further temperature rise

• There are 7 examples

1) Soil decomposition

• Carried out by bacteria which are dependent on enzymes, warmer temperature means enzymes can work faster

• CO2 is released by bacteria as they carry this out

1) Increase in temperature

2) Increase in rate of aerobic respiration

3) Increase in CO2

4) 1 again

2) Melting permafrost

1) High levels of greenhouse gases in the atmosphere cause global temperatures to rise

2) Increasing temp causes permafrost to thaw

3) Thawing exposes previously frozen organic matter to decay

4) As organic matter decays it releases CO2 (and sometimes methane) into the atmosphere

5) Atmospheric CO2 and methane levels increase

6) REPEATS

3) Ocean acidification

Nearly half the CO2 released into the atmosphere since the IR has been dissolved into the ocean

1) Increased CO2 in the atmosphere dissolves into ocean, producing carbonic acid

2) This reduces coral survival and reduces the carbon sequestration by coral

3) decreases the CO2 stored in carbonate of coral

4) More CO2 in ocean and atmosphere- repeats

4) Ice and snow melting

This impacts insulation

1) Increased snow and ice melt

2) Reduces surface albedo

3) Increases absorption of infrared radiation

4) Increased global temperatures

5) Repeats

5) Release of methane hydrate

Dead organic matter in deep sea sediment has decomposed and produced methane which forms a frozen solid methane hydrate

1) Atmospheric temps rise

2) Deep ocean temps rise

3) Methane hydrates stored in deep ocean sediments melt

4) Releases methane gas into the atmosphere so more infrared radiation is absorbed

5) Repeats

6) Increased forest and peat fires

Many peat bogs have waterlogged soils, when these warm they will dry out

1) Increase atmospheric temps

2) Peat and forest fires become more common

3) CO2 released into atmosphere from combustion

4) Repeats

7) Increase water vapour

Cirrus cloud- thin, wispy clouds, usually found at altitudes over 6000m. These clouds can reflect infrared energy emitted by the Earth’s surface and emit infrared produced from absorbed sunlight

1) Increased CO2 in earths atmospheric temperature

2) Increased ability of air to hold moisture

3) Increased evaporation

4) Increased water vapour

5) Increase in high altitude clouds increasing GHG effect

6) Repaeats

Tipping points

The concept that human actions cause climate change may cause changes in natural processes that themselves cause climate change to the extent that the human actions are no longer needed for climate change to continue

• If climate change is to be controlled it needs to be done before tipping points are reached

Examples of natural processes which may become uncontrollable:

• Faster soil decomposition

• Release of CO2 by forest and peat fires

• Snow on land melting, reducing albedo and warming occurring