Atmospheric Carbon

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The Greenhouse Effect

The Natural Greenhouse Effect keeps the earth at the optimum temperature to support life. Human activity has affected this, leading to impacts on temperature and precipitation.

Greenhouse gases

Greenhouse gases are gases that lead to the greenhouse effect.
These gases include methane (CH₄) and carbon dioxide (CO₂).
These greenhouse gasses are naturally emitted through respiration and out-gassing.

Natural greenhouse effect

Solar radiation enters the earth’s atmosphere it passes through the greenhouse gases layer.
This solar radiation is mostly absorbed by the earth's surface whilst some is reflected.
Some of this reflected radiation will pass back into space.
The greenhouse gas layer acts as a blanket, which stops the majority of this reflected radiation leaving the earth's atmosphere again.
This allows the Earth to be at a high enough temperature to support life.

Enhanced greenhouse effect

Human activity causes there to be an increase in greenhouse gases in the atmosphere.
- E.g. the burning of fossil fuels in vehicles.
These greenhouse gases add to the natural 'blanket' layer in the atmosphere.
This results in a larger amount of the reflected radiation being retained in the earth's atmosphere than normal, leading to warmer temperatures.

Impacts of the Greenhouse Effect

The greenhouse effect has impacts on the distribution of temperature and precipitation throughout the world.

Temperature distribution

Different locations on the Earth receive differing levels of solar energy.
The angle of the sun's rays result in the Equator receiving the most concentrated radiation, whilst at the Poles the same radiation is dispersed over a greater distance.

The albedo effect

The colour of the surface of the earth (how light or dark it is) impacts on how much radiation is absorbed.
This is called the albedo effect.
The white snow of glaciers and ice caps reflects the majority of heat whilst relatively dark oceans and forests absorb heat.
This heat is then redistributed via air circulation and ocean currents.

Precipitation distribution

The heating of the Earth’s surface leads to warm air rising, cooling, and condensing to form clouds.
The intense solar radiation at the Equator leads to warm air rising, causing high levels of rainfall all year.
At 30^oN and 30^oS, the air cools and sinks again resulting in high pressure where rainfall is rare.
At 60^oN and 60^oS, different air masses meet resulting in frontal rainfall.
The Poles are cold, resulting in air sinking, causing little rainfall.

Atmospheric regulation

Plants both in the ocean and on land are extremely important at regulating atmospheric carbon levels.

Photosynthesis' role

Marine phytoplankton sequesters around 5-15Gt of carbon a year.
Terrestrial primary producers sequester around 100-120Gt of carbon a year.
Tropical rainforests can sequester 2200g of Carbon per m² a year. This is significantly larger than open oceans.
Arctic sea ice melt is increasing, leading to greater areas of oceans being exposed to sunlight for longer, causing algal bloom. Algae sequesters CO₂ but alters marine ecosystems.

Soil health

The amount of carbon stored in the soil depends on:
- The size of the store in different biomes
- The total input (the amount of plant litter and animal waste)
- The total output (the amount of decomposition, erosion and uptake by plant growth).
Stored carbon is important for soil health. Healthy soil will be dark in colour, contain worms and organisms and have good infiltration rates.

Seasonal change

The cooler weather and reduced hours of sunlight means that there is less photosynthesis occurring, so less CO₂ is being taken up by the plants.
The difference in global atmospheric carbon is therefore higher in the winter than summer.
Climate change could mean that winters become shorter. If this is the case less CO₂ will be released.