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Global Ecology

Global Ecology. Chapter 23. Outline. Atmospheric Envelope Greenhouse Effect El Nino Effects Tropical Deforestation Human Influence on Atmospheric Composition Depletion and Recovery of the Ozone Layer. Atmospheric Envelope.

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Global Ecology

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  1. Global Ecology Chapter 23

  2. Outline • Atmospheric Envelope • Greenhouse Effect • El Nino • Effects • Tropical Deforestation • Human Influence on Atmospheric Composition • Depletion and Recovery of the Ozone Layer

  3. Atmospheric Envelope • The earth is wrapped in an atmospheric envelope that makes the biosphere a hospitable place. • Clean, dry air at the earth’s surface is approx: • 78.08 % Nitrogen • 20.94 % Oxygen • 0.93 % Argon • 0.003 % Carbon Dioxide • 0.00005 % Ozone

  4. Greenhouse Effect • Heat is trapped near the earth’s surface by greenhouse gases: • (Water Vapor, Carbon Dioxide, Methane, Ozone, Nitrous Oxide, and CFC’s)

  5. Greenhouse Effect • Greenhouse gases absorb infrared and reemit most back to earth. • 30 % Solar energy reflected back by clouds, particulate matter, etc. • 70 % Absorbed by atmosphere/surface.

  6. Greenhouse Effect • Three aspects of global change caused by humans: • Changes in the nitrogen cycle • Changes in landscapes • Changes in atmospheric carbon dioxide.

  7. A Global System • The El Niño Southern Oscillation (ENSO), a large-scale atmospheric and oceanic phenomenon, influences ecological systems on a global scale. • During El Niño, a warm current appears off the coast of Peru. • Generally during Christmas season • Southern Oscillation refers to oscillation in atmospheric pressure that extends across the Pacific Ocean.

  8. Historical Thread • Walker(1924) discovered the correspondence between barometric pressure across the Pacific and rainfall during monsoons. • Reduced barometric pressure in the eastern Pacific was accompanied by increased barometric pressure in the western Pacific and vice versa.

  9. Historical Thread • Bjerknes: UCLA professor connected El Niño and Walker’s Southern Oscillation. • The gradient in sea surface temperature across the central Pacific produces a large-scale atmospheric circulation that moves in the plane of the equator.

  10. El Niño and La Niña • ENSO is a highly dynamic, large-scale weather system that involves variation in sea surface temperature and barometric pressure across the Pacific & Indian Oceans. • This system drives climatic variability around the globe.

  11. El Niño and La Niña • During mature phase, the sea surface in eastern tropical Pacific is much warmer than average and barometric pressure over the eastern Pacific is lower than average. • Promotes formation of storms over eastern Pacific, and increased precipitation to much of North America.

  12. El Niño and La Niña • During El Niño, sea surface in the western Pacific is cooler than average and barometric pressure is higher than average. • Produces drought over western Pacific.

  13. El Niño and La Niña • La Niña: Periods of lower sea surface temperatures and higher than average pressure in eastern tropical Pacific. • Drought to much of North America. • Higher than average precipitation in western Pacific.

  14. El Niño and Marine Populations • Under average conditions, coastal waters are relatively cool along most of the west coast of South America. • Tongue of cool water extends westward. • Cool water brought to surface by upwelling. • Upwelling is driven by southeast trade winds along the coast and by east winds offshore.

  15. El Niño and Marine Populations • During an El Niño event, easterly winds slacken and the pool of warm water in the Pacific moves eastward. • This warm water shuts down the upwelling, reducing nutrient supply, and reducing phytoplankton production. • Reproductive failure, migration, death occurs in fish populations.

  16. El Niño and Marine Populations • Remote sensing of phytoplankton pigments in surface waters around the Galapagos Islands shows that the 1982-83 El Niño reduced the average primary production and changed the location of primary production hot spots.

  17. El Niño and Marine Populations • These changes in rate & distribution of primary production caused the reproductive failure, migration, and widespread death of seabird populations in the Galapagos and along the coast of South America.

  18. El Niño and Marine Populations • The 1982-83 El Niño also had an impact on fur seal and sea lion populations, through reductions in food supply.

  19. El Niño and Great Salt Lake • Strong El Niños of 1982-83 and 1986-87 were the source of many storms deep into interior of North America. • Increased precipitation with Great Salt Lake basin. • 1983-87 lake rose 3.7 m.

  20. El Niño and Great Salt Lake • Wurtsbaughand Smith Berry found lake salinity dropped by 50 g/l and the lake was invaded by predaceous insect Trichocorixa verticalis.

  21. El Niño and Great Salt Lake • The invasion of the predator induced a trophic cascade. • Predator reduced population of brine shrimp from 12,000 to 74 per m3. • Phytoplankton biomass increased significantly. • By 1990, lake level fell 2.8 m, and salinity returned to 100 g/l. • All ecosystem changes were reversed.

  22. El Niño and Kangaroo Populations • Red Kangaroos (Macropus rufus) occupy most of Australia’s semiarid interior. • During wet periods with plenty of food, females will simultaneously have a joey following, a younger offspring in the pouch, and an embryo waiting to enter the pouch.

  23. El Niño and Kangaroo Populations • Under marginal conditions, most young die soon after leaving the pouch. • If food becomes scarce, females stop lactating and young die in embryo stage. • Kangaroos breed quickly and young enter the pouch within 60 days of onset of significant rainfall.

  24. El Niño and Kangaroo Populations • By reproducing large numbers of offspring under favorable conditions, kangaroos increase the number of adults that will face El Niño induced droughts. • Cairns and Grigg found a tight coupling of M. rufus populations to El Nino.

  25. Human Activity and Global Nitrogen Cycle • As human civilization developed intensive agriculture and industrial processes, we began to manipulate nitrogen cycle on massive scale.

  26. Human Activity and Global Nitrogen Cycle • Vitousek tallied natural and manmade sources of nitrogen: • N - fixing bacteria/plants 100 Tg/yr • Marine environments 5-20 Tg/yr • Lightning 10 Tg/yr • Total Non-Human sources 130 Tg/yr • Nitrogen fixing crops 30 Tg/yr • Fertilizer industry 80 Tg/yr • Burning fossil fuels 35 Tg/yr • Total Human sources 145 Tg/yr

  27. Human Activity and Global Nitrogen Cycle • Nitrogen fixation resulting from human activity fixes more nitrogen than all other sources combined.

  28. Human Activity and Global Nitrogen Cycle • Human contributions to the global nitrogen cycle have increased exponentially. • Large scale nitrogen enrichment threatens the health of ecosystems and biological diversity.

  29. Change in Land Cover • Rapid changes in global patterns of land use threaten biological diversity. • Agriculture and urbanization have significantly altered 1/3 to 1/2 of the ice-free land surface of the earth.

  30. Tropical Deforestation • Tropical forests support at least half of earth’s species. • Skole and Tucker reported tropical forests occur in 73 countries and once covered 11,610,360 km2. • Brazil contains 1/3 of total. • Highest deforestation rate. • Estimated by 1978, 78,000 km2 deforested. • Annual rate of deforestation 1978-1988 was 15,000 km2.

  31. Tropical Deforestation

  32. Edge Effects and Tropical Deforestation • When a forest fragment is isolated due to cutting, its edge is exposed to greater amounts of solar radiation and wind. • Physical environment along forest edges is hotter and drier and solar intensity is higher. • Fragmentation decreases diversity of many animal groups.

  33. Edge Effects and Tropical Deforestation • The majority of old-growth temperate forests in north-western North America has been cut. • Deforestation not limited to tropical areas.

  34. Human Influence on Atmospheric Composition • Human activity is changing the composition of the atmosphere. • Most of the atmospheric increase in carbon dioxide is due to the burning of fossil fuels.

  35. Human Influence on Atmospheric Composition • Record of atmospheric composition during last 160,000 years was extracted from ice cores in Greenland and Iceland. • Samples of atmosphere trapped in ice. • Core indicated two very large fluctuations in atmospheric CO2 concentrations. • 140,000 years ago. • 13,000 years ago.

  36. Human Influence on Atmospheric Composition • Periods of low CO2 correspond to low temperatures experienced during ice ages, while high levels correspond to interglacial periods.

  37. Human Influence on Atmospheric Composition • During 19th and 20th centuries, concentration of atmospheric CO2 increased dramatically.

  38. Human Influence on Atmospheric Composition • Fossil fuel burning alone produces more than enough CO2 (5,600 Tg/yr) to account for recent atmospheric concentrations (3,500 Tg/yr). • Three major periods of interruptions: • World War I • Great Depression • World War II

  39. Human Influence on Atmospheric Composition • Burning fossil fuels adds CO2 with little 14C. • The concentration of 14C was fairly stable from 1700 until 1850. • After 1850, 14C concentrations in wood declined significantly.

  40. Depletion and Recovery of the Ozone Layer • In 1985, British Antarctic Survey discovered major reduction in atmospheric ozone. • Ozone absorbs potentially harmful ultraviolet light. • UV-B radiation – capable of destroying biological molecules.

  41. Depletion and Recovery of the Ozone Layer • Attention focused on stopping chlorofluorocarbons (CFCs). • As CFCs breakdown, they release chlorine, which can act as a catalyst to break down ozone molecules. • Each chlorine can break down many ozone molecules. • 1987 Montreal Protocol – reduce/eliminate human generated substances that deplete ozone.

  42. Depletion and Recovery of the Ozone Layer • As a result of the 1987 Montreal Protocol, global production of CFCs has been reduced from over one million tons annually to less than 50,000 tons in 2003. • Even after the protocol went into effect, the hole continued to grow. • Largest hole to date in 2000. • 2003 saw first reported evidence the ozone layer is recovering.

  43. The Future • During the past century, the average global temperature has risen 0.7°C. • It is predicted that without reductions in greenhouse gases, global temperatures will increase and additional 1.5° to 5.5°C over the next century.

  44. The Future • Predicted consequences of this global increase in temperature include: • Increased frequency of intense hurricanes • Melting glaciers – rising sea level • More intense, more frequent heat waves in temperate areas • Increased summer drought in semi-arid areas • Increased coral mortality • Potential spread of insect-transmitted diseases • Dieback of forests due to increased disease & insects • Increased wildfires • Widespread extinctions • Release of CO2 and CH4 from arctic soils, accelerating global warming

  45. The Future • Knowledge of ecology will play a key role in our quest to reduce and reverse the damage we have caused to our planet.

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