The causes of climate change


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The causes of climate change

  1. 1. Anthropogenic Climatic Attentuation Global Warming
  2. 2. A. The evidence of past climates
  3. 3. Paleo-environmental reconstruction • Step #1 – find your evidence • Step #2 – date your evidence • Step #3 – examine you evidence • All spread over a bed of nice….. • UNIFORMITARIANISM
  4. 4. What is Paleoclimatology? • Scientists take samples from the centre of the coral. Clipperton Atoll, • Paleoclimatology is the study of past climates. Since it is not possible to go back in time to see what climates were like, scientists use imprints created during past climate, known as proxies, to interpret paleoclimate. Microbial life, such as diatoms, forams, and coral serve as useful climate proxies. Other proxies include ice cores, tree rings, and sediment cores (which include diatoms, foraminifera, microbiota, pollen, and charcoal within the sediment and the sediment itself). • Past climate can be reconstructed using a combination of different types of proxy records. These records can then be integrated with observations of Earth's modern climate and placed into a computer model to infer past as well as predict future climate.
  5. 5. Step #1 – find your evidence • • • • How Are Microbes Used As Proxies? Foraminifera, such as this Globigerinoides species, can be used as a climate proxy (copyright O. R. Anderson, accessed from the Micro Scope website). Foraminifera, also known as forams, and diatoms are commonly used microbial climate proxies. Forams and diatoms are shelled microorganisms found in aquatic and marine environments. There are both planktonic, or floating in the water column, and benthic, or bottom dwelling, forms. Foram shells are made up of calcium carbonate (CaCO3) while diatom shells are composed of silicon dioxide (SiO2). These organisms record evidence for past environmental conditions in their shells. Remains of foram and diatom shells can be found by taking sediment cores from lakes and oceans, since their shells get buried and preserved in sediment as they die. The chemical make up of these shells reflect water chemistry at the time of shell formation. Stable oxygen isotope ratios contained in the shell can be used to infer past water temperatures. These oxygen isotopes are found naturally in both the atmosphere and dissolved in water. Warmer water tends to evaporate off more of the lighter isotopes, so shells grown in warmer waters will be enriched in the heavier isotope. Measurements of stable isotopes of planktonic and benthic foram and diatom shells have been taken from hundreds of deep-sea cores around the world to map past surface and bottom water temperatures. Researchers may also use foram and diatom population dynamics to infer past climate. Relative abundance as well as species composition in particular areas may indicate environmental conditions. Typically, warmer weather will cause organisms to proliferate. In addition, since each species has a particular set of ideal growing conditions, species composition at a particular site at a particular time may indicate past environmental conditions.
  6. 6. Step #1 – find your evidence • • How Are Other Proxies Used? Combinations of proxy data are generally used to reconstruct records for past climate. In addition to forams and diatoms, common proxies and their respective analytical methods include: Ice core records- deep ice cores, such as those from Lake Vostok, Antarctica, the Greenland Ice Sheet Project, and North Greenland Ice Sheet Project can be analyzed for trapped gas, stable isotope ratios, and pollen trapped within the layers to infer past climate. Tree rings- can be counted to determine age. The thickness of each ring can be used to infer fluctuations in temperature and precipitation, since optimal conditions for the particular species will result in more growth, and thus thicker rings for a given year. Scars and burn marks can indicate past natural events such as fire. Sediment cores- can be analyzed in many ways. Sediment laminations, or layers, can indicate sedimentation rate through time. Charcoal trapped in sediments can indicate past fire events. Remains of microorganisms such as diatoms, foraminifera, microbiota, and pollen within sediment can indicate changes in past climate, since each species has a limited range of habitable conditions. When these organisms and pollen sink to the bottom of a lake or ocean, they can become buried within the sediment. Thus, climate change can be inferred by species composition within the sediment
  7. 7. B. What are the causes of climate change?
  8. 8. The Greenhouse Effect
  9. 9. Match the letters to the numbered boxes on your diagram A B E Human activity increases concentration of GH gases, resulting in global warming F G C D H
  10. 10. The Greenhouse Effect & Global Warming 2 7 8 5 1 6 3 4
  11. 11. The Greenhouse Effect & Global Warming 2 7 8 5 1 6 3 4
  12. 12. The Greenhouse Effect & Global Warming 2 7 8 5 1 6 3 4
  13. 13. The Greenhouse Effect & Global Warming 2 7 8 5 1 6 3 4
  14. 14. The Greenhouse Effect & Global Warming 2 7 8 5 1 6 3 4
  15. 15. The Greenhouse Effect & Global Warming 2 7 8 5 1 6 3 4
  16. 16. The Greenhouse Effect & Global Warming 2 7 8 5 1 6 3 4
  17. 17. The Greenhouse Effect & Global Warming 2 7 8 5 1 6 3 4
  18. 18. The Greenhouse Effect & Global Warming 2 7 8 5 1 6 3 4 Human activity increases concentration of GH gases, resulting in global warming
  19. 19. The Causes 1. Earth-Sun Geometry is best • The Serbian astrophysicist Milutin Milankovitch • • known for developing one of the most significant theories relating Earth motions and long-term climate change. Milankovitch dedicated his career to developing a mathematical theory of climate based on the seasonal and latitudinal variations of solar radiation received by the Earth. Now known as the Milankovitch Theory, it states that as the Earth travels through space around the sun, cyclical variations in three elements of Earth-sun geometry combine to produce variations in the amount of solar energy that reaches Earth: – – – • Variations in the Earth's orbital eccentricity—the shape of the orbit around the sun. Changes in obliquity—changes in the angle that Earth's axis makes with the plane of Earth's orbit. Precession—the change in the direction of the Earth's axis of rotation, i.e., the axis of rotation behaves like the spin axis of a top that is winding down; hence it traces a circle on the celestial sphere over a period of time. Together, the periods of these orbital motions have become known as Milankovitch cycles.
  20. 20. The Causes 1. Earth-Sun Geometry
  21. 21. The Causes 1. Earth-Sun Geometry
  22. 22. 2. Volcanic eruptions Scientists are quite certain that over a period of several million years, increased volcanism can create enough dust and soot to block out sunlight and produce climatic change. 512,000 cubic km = the 1980 eruption of Mount St. Helens produced 1 cubic km of volcanic material. 60-65 Myr BP For instance at the end of the Cretaceous period and beginning of the Tertiary (known as the KT boundary) there was increased volcanic activity, with huge volcanic eruptions spewing forth floods of lava. The Deccan traps in India are an example of K-T boundary ruptures in the Earth's surface, which may have lead to the extinction of dinosaurs.
  23. 23. 2. Volcanic eruptions • Example: • Mt Pinatubo June 15, 1991, 20 million tons of SO2 and ash particles 12 miles (20 km) high into the atmosphere. • In the stratosphere circled the globe for three weeks.
  24. 24. 2. Volcanic eruptions • Large-scale volcanic activity may last only a few days, but the massive outpouring of gases and ash can influence climate patterns for years. Sulfuric gases convert to sulfate aerosols, sub-micron droplets containing about 75 percent sulfuric acid. Following eruptions, these aerosol particles can linger as long as three to four years in the stratosphere. Major eruptions alter the Earth's radiative balance because volcanic aerosol clouds absorb terrestrial radiation, and scatter a significant amount of the incoming solar radiation, an effect known as "radiative forcing" that can last from two to three years following a volcanic eruption. "Volcanic eruptions cause short-term climate changes and contribute to natural climate variability," says Georgiy Stenchikov, a research professor with the Department of Environmental Sciences at Rutgers University. "Exploring effects of volcanic eruption allows us to better understand important physical mechanisms in the climate system that are initiated by volcanic forcing."
  25. 25. Do they warm or cool?  COOLING - Scientists are quite certain increased volcanism can create enough dust and soot to block out sunlight and reduce global temperatures in the short term (several weeks). Further more, for several years volcanic sulphuric acid aerosol clouds can help reduce temperature through ‘radiation forcing’ by scattering the sun’s radiation. The eruption of Mt Pinatubo in 1991 (20 million tons of sulphur dioxide and ash particles blasted more than 20km high into the atmosphere) is believed to have reduced global temperature by 0.20.5C.
  26. 26. What about warming?  WARMING - In the very distant past, there have been volcanic eruptions so massive that they covered vast areas in lava more than a kilometre thick and appear to have released enough CO2 to warm the planet after the initial cooling caused by the dust. But even with such gigantic eruptions, most of subsequent warming may have been due to methane released when lava heated coal deposits, rather than from CO2 from the volcanoes.
  27. 27. What about the past 50 years? • Measurements of CO2 levels over the past 50 years do not show any significant rises after eruptions. Total emissions from volcanoes on land are estimated to average just 0.3 Gt of CO2 each year (a hundredth of human emissions).
  28. 28. 3. Solar output
  29. 29. Relative to 1961-1990 average Relative to 1961-1990 average
  30. 30. Some interesting links Ecologists’ own goal: ozone saver is global warmer Great Global Warming Swindle 12345678 Erratum – Wikipedia's summary of the case against the film Inconvenient Truth Erratum – Wikipedia's summary of the case against the film
  31. 31. Who is to blame?
  32. 32. Emissions v Population (% ) 30.0 25.0 % of global CO2 emissions 15.0 % of global population 10.0 5.0 lia tr a Au s ad a C an U K di a In pa n Ja C hi na ex -U SS R Eu r op e 0.0 U SA % 20.0
  33. 33. Wealth v Pop:Gas ratio Pop : CO2 ratio 6.0 5.0 4.0 3.0 2.0 1.0 0.0 0 5000 10000 15000 GDP ($) 20000 25000