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HUMANS AND ENVIRONMENTAL CHANGE. Learning objectives: Appreciate how the increase in human populations has altered the vegetation cover of the planet Describe the history of the human-environment interaction over the last 2 centuries

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humans and environmental change
  • Learning objectives:
    • Appreciate how the increase in human populations has altered the vegetation cover of the planet
    • Describe the history of the human-environment interaction over the last 2 centuries
    • Understand how the use of fossil fuels has impacted upon the climate
    • Describe how the carbon and nitrogen cycles have been perturbed
    • Describe the predictions of the impact of climate change on life on the planet
  • Environmental problems throughout civilization
    • Coal and wood burning throughout civilisation
    • Romans – metals caused a health hazard
    • Acute problem in industrial era – smog
      • Clean Air Act of 1957 when 4000 Londoners died in one week due to smog episode
    • Problems exacerbated with growth in motor cars
  • Environmental change on a global scale became a matter of public concern in the 1960’s
    • Silent Spring 1962 – Rachel Carson
    • DDT
    • Environmental change became part of western culture and international research agenda
land use population and food supply
Land Use, population and food supply
  • Malthus (1766-1834)
    • Growing population → resource depletion → starvation
  • Meadows et al. (1972) – The Limits to Growth
    • Neomalthusian
    • But their report failed to emphasise what is now important
  • So, what is the land use, food supply and population relationship?
  • Historical perspective
    • Agriculture flourished in many regions (e.g. China 8000 yrs ago)
    • Ships and navigation allowed colonisation
    • Modern era – explosive population growth
      • Increase in economic activity, energy usage, science and technology
      • Slow growth in rich countries, rapid growth in poor countries
  • Populations requirement for land
    • 6 billion people use about ⅓ of the land for grazing and crops
    • Achieved via removal of natural vegetation (wood, grasslands)
  • Deforestation
    • Occurred over hundreds of yrs (esp Europe and N America)
    • Extent is hard to assess, lack historical records (except palynology)
    • Presently widescale tropical deforestation
      • Extent is not well known except where remote sensing is used
      • Average = 5-6 million hectares per yr (0.5%/yr)
  • Climatic changes – from large scale alteractions from forest to farm
    • Complex interactions not fully understood
    • Release CO2, alters albedo, transfer of water to atmosphere
    • Forest protect soil from erosion

Figure 21.2

Source: After Moore et al.,1996


Figure 21.2cont.

Source: After Moore et al.,1996


Figure 21.2cont.

Source: After Moore et al.,1996


Table 21.3

Source: Compiled from data in Achard et al., 2002

climate change long term
Climate change: long term
  • Climate has always fluctuated
  • Evidence
    • Historical records, dendrochronology, palynology
  • Long term gradual changes - Milankovitch cycles
  • Catastrophic changes – mass global extinctions
    • Late Permian (245 million yrs ago) ½ families of marine animals lost
    • Cretaceous–Tertiary (KT) boundary (65 million yrs ago) – 75% plant species lost, 15% marine families, dinosaurs became extinct
    • Attributed to comets and asteroids throwing debris into atmosphere and causing global cooling, reduction in photosynthesis and collapse of food chains.
recent and future changes feedbacks and greenhouse gases
Recent and future changes: feedbacks and greenhouse gases
  • Intense area of research
  • Unprecedented rate of global warming = current concern
    • 0.7oC temperature rise over the last century
    • Glacier retreat, sea level rise, phenological changes
    • Linked to anthropogenic changes in atmospheric composition
  • ‘Greenhouse effect’
    • Without it the water on the planet would be mostly ice
    • CO2, NH4, N2O, water vapour, CFC’c
    • International acknowledgement Kyoto Protocol
  • Ozone depletion
  • Positive feedbacks
    • Warming causes increase CO2 release from biomass decomposition
    • Warming melts snow and increases global albedo
    • Tropical deforestation causes warming and drying and further forest decline
    • Warming causes decomposition of gas hydrates and methane release
  • Negative feedbacks
    • Deforestation causes increased soil erosion – atmospheric aerosol input, causing cooling
    • Increased transpiration in warm conditions causes more clouds, cooling the planet
    • Increased precipitation and ice melt increases fresh water runoff into sensitive parts of the oceans slowing down circulation into northern high latitudes

Figure 21.5

Source: After IPCC, 2001


Figure 21.6

Source: After IPCC, 2001

the carbon cycle
The carbon cycle

Figure 21.8

  • The various pools differ in magnitude and time a carbon atom resides in them – the dynamic behavior is complex
    • ‘average’ carbon atom resides in atmosphere for 5 yrs and ocean for 400yrs
  • Understanding the carbon cycle is vital to understanding all life
    • Principal constituent of all cells
    • Carbon content of dry biomass = 45-55%
  • Anthropogenic CO2 emission can force cycle out of equilibrium
    • 8 gigatons of carbon per yr are emitted from fossil fuel burning and clearing forests
    • 3 gigatons taken up by photosynthesis or dissolving in oceans – ‘sink’
    • Some prospect of enhancing sinks to slow down climate change
      • Planting forest, change agricultural practices to conserve carbon
      • Fertilising the ocean to increase phytoplankton productivity
the nitrogen cycle
The nitrogen cycle
  • Nitrogen is essential for life
    • Important constituent of proteins and nucleic acids
  • Unreactive dinitrogen (N2) = 79% of the atmosphere
  • Reactive N = ammonia (NH3), oxides NO, NO2, N2O
  • 2 processes covert N to reactive forms taken up by plant roots:
    • Lightening
    • Biological nitrogen fixation
      • Converts the largest amount
      • Bacteria – either freeliving or symbiotic with plants (leguminosae)
    • Cyclical processes
  • Human impact
    • Fertiliser (Nitrous oxide released as a GHG)
    • Internal combustion engines
    • Causes enhanced ammonia and nitrogen deposition, may increase plant growth or cause nutrient imbalance in acid rain

Figure 21.10a

Source: After Galloway et al. (1995) in Global Biogeochemical Cycles, 9,

Fig 3 and Fig 6


Figure 21.10b

Source: After Galloway et al. (1995) in Global Biogeochemical Cycles, 9,

Fig 3 and Fig 6

destruction of the ozone layer by cfc s
Destruction of the ozone layer by CFC’s
  • UV radiation is absorbed by DNA causing damage to the genetic code and interfering with protein synthesis and the control of cell division
    • Reduces immune system, causes skin cancer and damage to eyes
  • For the last billion yrs the Earth has been shielded from UV by ozone (O3) in the stratosphere – enabling life to develop on land
  • Ozone is diminishing from a chain of chemical reactions that begins with human induced chemicals – chloroflourocarbons
    • Inert and persist in the atmosphere
    • Cause breakdown of O3 to O2
  • Survey of ozone depletion began in the Antarctic in 1957 (ozone layer is thinnest at the poles)
  • Montreal Protocol 1987 – nations agreed to phase out CFC use
    • Hydroflourocarbons (HFC’s) and perflourocarbons (PFC’s) introduced
loss of biodiversity
Loss of biodiversity
  • Defined as the number and variety of species in ecological systems
  • Human activities are causing decline in species numbers (esp land use)
  • Impossible to know exact number of species but extinctions are generally well-documented
    • Since 1600, 490 plants and 580 animals extinct
  • Why is it important?
    • Keystone species – critical role in the ecosystem
    • Potential and actual economic importance (genetic pool)
    • Any species may be part of a human life-support system
  • Most species live in the tropics – where most disturbance is now occurring
  • ‘Hotspots’
    • Number of species threatened far exceeds our capacity to protect
    • Therefore need to concentrate conservation efforts in areas of high diversity
  • Future – climate change is likely to cause diversity loss from tropical forests
the future
The future
  • 1972 Club of Rome warned of the dangers faced by the world
    • threat of nuclear war at the time
  • Now – climate change is the main concern
    • Developing world is increasing in population and resource use
    • Optimism of nuclear power has been lost
      • nuclear accidents and cost of waste disposal
  • Reasons for optimism
    • Alternative sources of energy were developed between 1960-2000
    • Greater understanding of environmental systems
    • Humans are finally starting to accept human-environment relationships
  • World population growth has been associated with increased utilisation of the land for agriculture and deforestation
  • Human’s now consume or dominate 40-50% of the land’s biological production
  • Large scale changes in the land surface influence regional and global climates
  • Fossil fuel burning and chemicals such as CFC’s and nitrogen fertilisers all impact on the environment
  • Positive and negative feedbacks of the global environmental system
  • Technological improvements are continuously being made that may help cope and mitigate against environmental change
  • Increasing international recognition of environmental change