HUMANS AND ENVIRONMENTAL CHANGE

1. 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

2. Introduction • 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

3. 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

4. Table 21.1

5. …cont • 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

6. Figure 21.2 Source: After Moore et al.,1996

7. Figure 21.2cont. Source: After Moore et al.,1996

8. Figure 21.2cont. Source: After Moore et al.,1996

9. Table 21.3 Source: Compiled from data in Achard et al., 2002

10. Figure 21.3

11. 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.

12. Figure 21.4

13. 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

14. …cont • 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

15. Figure 21.5 Source: After IPCC, 2001

16. Figure 21.6 Source: After IPCC, 2001

17. Table 21.4

18. The carbon cycle Figure 21.8

19. ..cont • 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

20. Table 21.5

21. 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

22. Figure 21.9

23. Figure 21.10a Source: After Galloway et al. (1995) in Global Biogeochemical Cycles, 9, Fig 3 and Fig 6

24. Figure 21.10b Source: After Galloway et al. (1995) in Global Biogeochemical Cycles, 9, Fig 3 and Fig 6

25. 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

26. 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

27. 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

28. Summary • 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