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

Impact of Increasing Demand for Food, Fuel & Other Resources

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 means 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

  • Since pre-industrial times the ocean pH has dropped from 8.2 to around 8.1, a 26% increase in acidity

• Ocean acidification increases the risk of marine ecosystems reaching a critical threshold of permanent damage

  • Coral, shellfish, sea urchins and pteropods all build shells or skeletons from calcium carbonate

  • As the pH drops, carbonate ion concentration falls, making it harder for these organisms to calcify and causing existing shells to dissolve

• 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 bleaching events are becoming more frequent; the Great Barrier Reef has lost over 50% of its coral cover since 1995

• Coral reefs are also affected by ocean acidification

  • This impacts coastal fishing communities in developing countries that are highly dependent on reef ecosystems and shellfish harvesting

• Some species of phytoplankton and seagrass benefit from higher CO₂ concentrations, growing more rapidly

• This may partially offset food web losses, but ecosystem restructuring may reduce biodiversity

Enhanced Greenhouse Effect

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 the 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 the 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