A Balanced Carbon Cycle (Edexcel A Level Geography)

Human Interference

• A balanced carbon cycle is vital in sustaining other systems on earth 
• The carbon cycle plays an important role in regulating global temperatures and climate by controlling the amount of carbon dioxide in the atmosphere which in turn affects the hydrological cycle

The Greenhouse Effect

• The natural greenhouse effect is influenced by the concentration of atmospheric carbon (carbon dioxide and methane)
• The Earth’s climate is driven by incoming shortwave solar radiation
• Around 31% is reflected by clouds, aerosols and gases in the atmosphere and by the land surface
• The remaining 69% is absorbed with half being absorbed at the surface (e.g., oceans) and the other half is re-radiated into space as long-wave radiation 
• However, much of this long-wave radiation is deflected back to the Earth’s surface by clouds and greenhouse gases 
• This ‘trapping’ of long-wave radiation creates the natural greenhouse effect allowing life to be supported on Earth
• If the amount of carbon dioxide and methane increases then more long-wave radiation will be trapped causing global temperatures to rise

The Greenhouse Effect

Ocean & Terrestrial Photosynthesis

• The carbon cycle is dependent on ocean and terrestrial photosynthesis in regulating the composition of the atmosphere
• Plants photosynthesising play a vital role in helping to keep carbon dioxide levels relatively constant thus helping to regulate average global temperatures
• As a result, patterns in plant productivity and carbon density are evident
• Highest productivity NPP occurs either in warm and wet regions such as the tropical rainforest or in shallow ocean waters

Soil Health

• Soil health relies on the amount of organic carbon stored in the soil which is dependent on:
• The inputs - plant and animal residues and nutrients
• The outputs - decomposition, erosion and use in plant and animal productivity

Nutrient Cycle

• Carbon, within soil organic matter, helps provide soil with its water retention capacity, its structure and fertility
• Soil erosion is a major threat to carbon storage and soil health as organic carbon is mainly found in the surface soil layer

Fossil Fuel Combustion

• Fossil fuels have been burnt at an increasing rate since the Industrial Revolution and remain the main energy source

Global Fossil Fuel Use

• Without human activity, the carbon in fossil fuels would flow into the atmosphere very slowly through volcanic activity
• However, the burning of fossil fuels has increased this flow from slow to fast carbon cycling
• The balance of the carbon cycle has been altered by the burning of fossil fuels which has various impacts on:
  • Global climate
  • Ecosystems 
  • The hydrological cycle

Implications for the Climate

• The IPCC report in 2014, explicitly linked gas concentrations to fossil fuel emissions, rising global temperatures and sea levels
• Changing temperatures and salinity levels of the oceans, as a result of global warming, could affect the thermohaline current
• The North Atlantic Drift (NAD), also known as the Gulf Stream could slow or reverse
• The NAD keeps the UK temperatures 5°C higher than they would be otherwise during the winter

Implications for Ecosystems

• Ecosystems help regulate carbon and hydrological cycles as well as providing goods and services for humans and the planet
• Already, species with low population numbers, limited climatic ranges or restricted habitats are at risk
• Marine ecosystems are threatened by lower oxygen levels, higher rates of ocean acidification and food chain changes (resulting from rising temperatures)
• Coastal ecosystems are at risk from sea level rise
• Although most species will be impacted negatively, there are some that may benefit
• Cool, moist regions (e.g., UK) could provide habitats for more species

Implications for the Hydrological Cycle

• The hydrological cycle’s flows and stores are vulnerable to global warming

Changes to the Hydrological Cycle