A balanced carbon cycle is important in sustaining other Earth systems but is increasingly altered by human activities

The Natural Greenhouse Effect
– A natural process that warms the Earth’s surface.
– When the Sun’s energy reaches the Earth’s atmosphere, some of it is reflected back into space and the rest is absorbed and re-radiated by greenhouse gases, such as water vapour, carbon dioxide and methane.
– The absorbed energy warms the atmosphere and surface of the Earth, maintaining global temperature at around 33 degrees Celsius warmer than it would otherwise be.
– CO2 is the most common greenhouse gas, accounting for 88% of the total.
– This can then be exacerbated by human activity, such as burning fossil fuels and agriculture which release greenhouse gases into the atmosphere, contributing to the enhanced greenhouse gas effect

Greenhouse Gases
– Carbon dioxide – 89% of greenhouse gases, 20% will stay in atmosphere for 800 years, released through burning fossil fuels and deforestation.
– Methane – stays in the atmosphere for 10 years, 7% of greenhouse gases, released through cattle and rice farming.
– Nitrous oxide – stays in the atmosphere for 100 years, 3% of greenhouse gases – released through jet aircraft and fertilisers.
– Halocarbons – 1% of greenhouse gases, used in industry, solvents and cooling equipment.

IPCC (Intergovernmental Panel for Climate Change)
– Believe human influence on the climate system is clear. At least half the observed warming since 1950 is as a result of human activity.
– The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen.
– Increase in anthropogenic GHG emissions have been driven by large economic and population growth.
Climate Patterns
– Amount of solar energy reaching the Earth’s surface varies in different locations, influencing temperature.
– Different characteristics of the Earth’s surface (e.g. light or dark) affect how much heat is absorbed or reflected – albedo.
– Solar radiation is most intense over the Equator, where rainfall is high all year, due to low air pressure.
– As air pressure rises, precipitation decreases.
– In the mid-latitudes, a mixture of characteristics meet and low pressure brings rainfall.
– Precipitation decreases in polar regions due to air cooling further and being dense and dry.

Regulating the composition of the atmosphere
– Photosynthesis is a vital process.
– Phytoplankton in oceans sequester CO2 through photosynthesis – pumping it out of the atmosphere and into the ocean store.
– Terrestrial photosynthesis allows plants to sequester carbon – released back into atmosphere through respiration and decomposition.
– Tropical rainforests and coral reefs are ideal for plant growth, promoting photosynthesis.
– In contrast, deserts have sparse vegetation, so little photosynthesis occurs.
The altered balance of carbon pathways and stores
– Precipitation in the form of snow could diminish, and rainfall and river discharge patterns may change – with greater flooding in winter and drought in summer.
– Increased thawing – accelerated the process of carbon release – faster pathway is emerging.
– Positive feedback – permafrost thaws – releasing more methane into the atmosphere – increased GHG concentrations reinforce global warming.

– short-term balance is reached.
Soil and Carbon
– Organic material is the way in which carbon passes through the system.
– Amount of carbon stores in the system depends on difference between inputs and outputs and size of the stores depends on different biomes.
– Healthy soils are usually dark, contain many worms/organisms, contain more carbon, retain moisture and provide air, water and nutrients for micro-organisms and plants to thrive.
Ecosystem productivity
– Around 1% of solar insolation reaching Earth is captured by photosynthesis and used by plants to produce biomass.
– The rate at which plants produce biomass is called primary productivity.
– Tropical rainforests have high primary productivity, whereas tundra ecosystems have lower productivity.
– If sources and sinks are equal, the carbon cycle is in equilibrium, stabilising global temperatures as the level of atmospheric carbon is steady.
– Human activities have increased inputs, causing a potential imbalance and rising temperatures.

Possible Exam Questions related to this Enquiry Question
– (Referring to a diagram of the carbon cycle) Explain how carbon moves from one store to another within the cycle. (6)
– Explain the role soil plays in the carbon cycle. (6)
– Explain the significance of carbon dioxide in maintaining the greenhouse effect. (6)
– Explain the processes by which carbon is released into the atmosphere. (8)
– Asses the significance of carbon sequestration within the carbon cycle. (12)
– Assess the potential environmental impacts of increased warming through enhanced climate change. (12)