Human Activity on Carbon & Water Cycles (Edexcel A Level Geography)

Growing Resource Demands

• The biosphere sequesters about one quarter of fossil fuel carbon emissions every year, slowing down the rate of global warming
• However, the biosphere’s capacity to sequester carbon dioxide is being reduced due to land conversion 
• Land conversion is being driven by an increasing demand for food, fuel and other resources

Deforestation

• Forests cover 30% of the Earth’s land area and absorb rainfall and increase groundwater storage
• Deforestation occurs for either the timber or the space they occupy and is driven by the increasing demand for commodity production

• An estimated 10 million hectares are deforested every year
• Deforestation has impacts on the water cycle:
• Reduced interception by vegetation so infiltration to soil and groundwater changes
• Increased erosion and surface run-off, increasing sediment eroded and transported into rivers
• Deforestation has impacts on the carbon cycle:
• Reduced storage in soil and biomass
• Reduced carbon dioxide intake during photosynthesis
• Increased carbon influx to atmosphere by burning and decomposing vegetation

Afforestation

• Afforestation and reforestation are beneficial for carbon dioxide sequestration but can be controversial in its impacts:
• Commercial trees such as palm oil often store less carbon, use more water and are prone to disease

Grassland Conversion

• There are two main types of grassland which cover 26% of the Earth’s land area
  • Temperate grassland - no trees and a seasonal growth pattern linked to a large annual temperature range e.g. North America
  • Tropical grassland or Savannah- scattered trees with a wet and dry season e.g. Africa’s serengeti
• When grasslands are used too intensively for animals or agriculture it disrupts the carbon and water cycles
  • Rapid increase in population and changes from nomadic to sedentary farming along with the impacts of climate change and poor land management 
  • Soil and ecosystem degradation is now becoming a worldwide issue which is leading to a loss in carbon storage

Ocean Acidification

• Oceans are important carbon sinks but due to their increasing uptake of carbon dioxide from the atmosphere, their overall pH is decreasing leading to ocean acidification
• The acidity of the ocean today is estimated to be on average about 25% greater than it was during pre-industrial times
• Ocean acidification increases the risk of marine ecosystems reaching a critical threshold of permanent damage
• Ocean acidification will be exacerbated by other factors including warming temperatures, tropical storms and pollution
• Ecosystem resilience is important - if the rate of acidification is slow enough, the organisms may be able to adapt to the changes and be more resilient
• The Arctic Ocean is likely to be affected first due to its low pH threatening its ‘cold’ corals
• Globally, coral reefs are already experiencing bleaching from increasing temperatures
• Coral reefs are also affected by ocean acidification

The impacts of Ocean Acidification on Coral Reefs

Climate Change

• There is clear evidence that human activity is causing the enhanced greenhouse effect which is leading to climate changes
• Climate change may increase the frequency of drought due as a result of shifting climate belts, which will have an impact of the role of forests as carbon stores
• There are around 30 different climate zones which can be simplified as:
• Equatorial
• Tropical
• Temperate
• Polar
• These climate zones are not static and the increasing of earth’s temperatures could lead to 5% of the Earth’s land area shifting to a new climate zone
• There is already evidence of the expansion of subtropical deserts and poleward movement of stormy wet weather in mid-latitudes.

The Amazon's Changing Climate

• The Amazon acts as a global and regional regulator, pumping 20 billion metric tonnes of water into the atmosphere every day
• Since 1990, a more extreme cycle of drought and flood has developed in Amazonia, which can be linked to shifts in the Inter-tropical Convergence Zone (ITCZ)
• Rainfall has noticeably decreased downwind of deforested areas leading to São Paulo suffering a water crisis
• The Amazon rainforest which is already affected by deforestation is now being hugely impacted by droughts in 2005 and 2010