1. Global Warming

2. Climate
Climate: the average weather conditions over a period of years in a particular place
Climate is influenced by a variety of processes, including geologic processes
Volcanism
Sea-floor spreading
Configuration of landmasses due to plate tectonics
Climate changes impact geologic processes
Rates of erosion and deposition
Types of sediments deposited and sedimentary rocks formed
Geomorphology (surface features)
Fossil record

3. The Climate System Multidimensional System, many interacting parts
Atmosphere, hydrosphere, geosphere, biosphere, and cryosphere
Exchange of energy and moisture

4. The Climate System

5. Paleoclimatology – the study of past climates.
Earth’s climate varies in cyclical fashion over a number of time-scales
The study of natural climate processes is important to understand the role of humans in climate change.
Scientists measure climate change in the past in many different ways, depending on the time-scale.

6. Paleoclimatology – Study of past climates
What can paleoclimatology tell us about climate change that is relevant to society in the future?

7. Is the last century of climate change unprecedented relative to the last 500, 2000, and 20,000 years?
Do recent global temperatures represent new highs, or are they just part of a longer cycle of natural variability?
Is the recent rate of climate change unique to the present or was it commonplace in the past?
Can we find evidence in the paleoclimate record for mechanisms or climate forcings that could be causing recent climate change? 7

8. Proxy Climate Indicators
Instrumental records (from thermometers, rain gauges, etc.) only exist for the last 150 years.
Proxy climate indicators provide indirect indications of climate change. These include:
Seafloor Sediments
Oxygen Isotopes
Glacial Ice Cores
Corals
Pollen
Historical Data

9. Proxy climate indicators and their useful time range
Figure 21.5 Several methods, each with its own useful time range, allow scientists to determine historical and ancient climates. Source: Adapted with permission from T. Webb III, J. Kutzbach, and F. A. Street-Perrott in Global Change,T. .F. Malone and J. D. Roederer, eds.,pp. 212–218. Copyright 1985 by Cambridge University Press, U.K.

10. Climate Data from Historical Records
Wine is a serious business in Europe! Careful records of the first day of the grape harvest in Europe have been kept since the 14th century. Trends in these records show changes in climate, as the harvest started earlier or later in the year.

11. Tree rings Trees can live for thousands of years.
The width of tree rings provides information about growing conditions, including temperature conditions and CO2 concentrations.

12. Oxygen Isotope Analysis
One of the most important ways that proxy data indicators reveal climate information is through the use of oxygen isotope analysis.

13. Oxygen Isotope Analysis
Isotope – varieties of an element with different numbers of neutrons, resulting in different atomic masses.
The most common isotope of oxygen has an atomic mass of 16 and is called 16O. A heavier, less common variant is 18O. Both occur naturally, and neither is radioactive. You breathe both kinds. Both isotopes bond with 2 hydrogen atoms to make water, H2O.
Water made of 16O evaporates more easily. Water made of 18O condenses more easily.
18O has two extra neutrons

14. Oxygen Isotope Analysis
During colder weather, more light 16O evaporates, leaving ocean water with more heavy 18O.
This oxygen is incorporated into coral, plankton shells and sediments at the ocean bottom.
In colder climates, these proxy indicators will be enriched in 18O.
The ratio of 18O to 16O, (δ 18O) can be correlated to temperature. For benthic (deep-water sediments), colder temperatures are related to higher values of δ 18O.

15. Reading the Graph
Horizontal (x) axis: Note older data as you move right.
Left vertical (y) axis - δ 18O ratios. A value of zero indicates the “standard” value for ocean water. The higher the value, the more 18O, and the colder the ocean waters. Note colder is down on this graph.
Right vertical (y) axis - ∆T (temperature difference from “normal” annual average ocean temperature) Zero (dashed line) indicates “normal”.

16. Oxygen Isotope Analysis
Conversely, glacial ice cores are made of evaporated water that precipated.
Precipitation water always has a negative value of of δ 18O.
Colder temperatures are related to lower (negative values) of δ 18O.
The arrow points to a sudden cooling event that occurred over , 000 years ago, known as the Younger Dryas Event.

17. Great website explaining oxygen isotope analysis

18. Left: The type of fossil can indicate the temperature range in ocean waters.
Their shells can be analyzed chemically to measure CO2 concentrations and oxygen isotope ratios
Oxygen isotope analysis (below): the ratio of O-18 (heavier, less common) to O-16 (lighter, more common) is a proxy measurement of temperature.

19. Ice Cores – a very valuable proxy data indicator
Ice cores have annual rings, like trees, so age of core can be determined
Air bubbles trapped in the ice can be analyzed for oxygen-isotope data, carbon dioxide concentration, presence of aerosols etc.
The ice itself can be melted and analyzed for these proxy data indicators.
Figure 21.6 Scientists remove an ice core from a glacier in Greenland. Studies of ancient ice provide information about past climate. 19

20. Vostok Ice Core Data
This is partial data from an ice core from Antarctica.
Temperature data from oxygen/hydrogen isotopes.
Interglacial” is a warm period between ice ages.
Peak of last ice age about 20,000 years ago.

21. The modern atmosphere Two most abundant gases:
Less abundant gases (< 1%)
Argon
Water vapor
CO2 (only about .035%) It’s up to almost .040% now!
Non-gaseous components
water droplets
dust, pollen, soot and other particulates

22. FIGURE 17.6 Composition of the modern atmosphere.
Fig. 17.6, p.437

23. Thermal Structure of Atmosphere: Upper Layers
Troposphere - Extends to about 12 km (40,000 ft) elevation. Where we live.
Stratosphere – heated primarily by solar radiation
Ozone (O3) layer absorbs UV energy, causing temperatures to rise
Above 55km (stratopause) temps fall again
Mesosphere – thin air (can’t absorb energy), very cold up to 80km
Thermosphere – above 80km, temps rise rapidly (to just below freezing!)

24. Solar Energy (Insolation)
Also called solar radiation, although NOT radioactive!
Composed of electromagnetic waves with different properties depending on wavelength, frequency
Longwave (low frequency): includes heat (infrared), radio waves
Shortwave (high frequency): includes visible light as well as ultraviolet, x rays, gamma rays
Electromagnetic spectrum – shows EM wavelengths by frequency and wavelength.

25. Electromagnetic Spectrum

26. Solar Radiation in the atmosphere
Reflection/scattering – bounces off with no effect
Absorption – eventual re-emission in a different form

27. Reflection and Albedo
Reflection–electromagnetic radiation bouncing of from a surface without absorption or emission, no change in material or energy wavelength
Albedo – proportional reflectance of a surface
a perfect mirror has an albedo of 100%
Glaciers & snowfields approach 80-90%
Clouds – 50-55%
Pavement and some buildings – only 10-15%
Ocean only 5%! Water absorbs energy.

28. Typical Albedos of Materials on the Earth
Figure 18.4 The albedos of common Earth surfaces vary greatly.

29. Absorption and Emission
Absorption of radiation – electrons of absorbing material are “excited” by increase in energy
Increase in temperature; physical/chemical change
Examples: sunburn, cancer
Emission of radiation – excited electrons return to original state; radiation emitted as light or heat
Earth absorbs short wave radiation from sun (i.e. visible light) and emits longwave (infrared or heat) into the atmosphere.

30. Figure 18.7 The greenhouse effect can be viewed as a three-step process. Step 1: Rocks, soil, and water absorb short-wavelength solar radiation, and become warmer(orange lines). Step 2: The Earth re-radiates the energy as long-wavelength infrared heat rays (red lines). Step 3:Molecules in the atmosphere absorb some of the heat, and the atmosphere becomes warmer.

31. “Greenhouse gases” (water vapor, carbon dioxide, methane, etc
“Greenhouse gases” (water vapor, carbon dioxide, methane, etc.) let shortwave energy pass, but absorb longwave energy radiated upward by the Earth. The longwave energy is then re-radiated by the gases in all directions, some of it returning to the Earth’s surface.

32. The greenhouse effect keeps our atmosphere at a livable temperature of about 15 degrees C (59 degrees F). If all heat escaped, the average temperature of Earth would be about -200 C (00 F).

33. How CO2 in atmosphere relates to temperature

34. How CO2 in atmosphere relates to temperature

35. Human Impact on Climate
Our planet has been through many cycles of climate change in the past.
At the present time, we are undergoing a period of global warming.
There is almost no disagreement on this point in the scientific community.

36. Human Impact on Climate
Most also agree upon that there has been an increase in greenhouse gases, notably CO2 in the Earth’s atmosphere, and that human activity is responsible for at least a part of it.
It has been shown that CO2 and temperature are related.

37. The Controversial Questions
Is this increase part of a natural cyclical process, such as has occurred in the geologic past?
Or, is human activity primarily responsible?

38. Until the 19th century, ice core data show atmospheric CO2 levels at less than 300 parts per million (ppm)
Rapid increase in CO2 concentrations since the Industrial Revolution (mid 19th century) is apparent
Present-day levels exceed 390 ppm. This represents a 30% increase.

39. In 1958, Roger Revelle and Charles David Keeling started direct monitoring of atmospheric CO2 from the Mauna Loa Observatory.

41. Addition of Keeling Curve to the Vostok Ice Core Data

42. Comparison, using thermometers for temperature data and direct sampling of atmospheric CO2

43. Temperature Deviation Map for 2009. Note Arctic

44. Does this mean that human activity is responsible for global warming?

45. Those who say Yes would argue the following:
The Earth’s yearly average temperature has increased in the last century.
Atmospheric concentration of CO2, a principal greenhouse gas, has increased since the mid-19th century (the Industrial Revolution). Rise has been especially rapid since the 1950s.
It is a known fact that humans emit carbon dioxide into the atmosphere due to transportation and industrial processes.
Loss of forested land exacerbates this process, since photosynthesis is a process that removes CO2 from the atmosphere.

46. And those who would say No?
Is it possible that Global Warming is occurring naturally?
It is only through the reconstruction of past climates that we can truly evaluate the magnitude of this present warming trend.

47. Ocean temperatures from 60 million years ago
Climate change is the norm, not the exception.
Overall trend in the Cenozoic Era (Age of Mammals) has been a temperature decrease.
For the last 800,000 years, the planet has alternated between cold ice ages and warmer interglacial periods.
Compare last interglacial period at about 120,000 years ago to present.

48. Evidence of past temperature comes from multiple sources

49. Which came first, the increase in CO2 or the increase in temperature?

50. American Impact on Climate Adds up to over 16 metric tons annually

51. CO2 emissions by country (1995)
Emissions by country. In the last year, China has overtaken us.
Present Populations
China: 1300 million
US: million

52. CO2 emissions by country (1995) B
CO2 emissions by country (1995) B. Per capita emissions by country US number closer to 40 metric tonsHaves vs. have-nots

53. The Kyoto treaty on greenhouse warming
Dec. 1997, 160 nations met to discuss global warming
By Feb a treaty was ratified by many of them
Creates a global trading market for CO2 emissions
Sets limits and goals
Caps and goals tied to nations’ economies
Developing nations, eg China, India excluded from CO2 caps

54. Figure Fifty-five nations representing 55 percent of all industrial carbon dioxide emissions are needed to ratify the Kyoto Protocol.
Fig , p.521

55. 21.9 The Kyoto treaty on greenhouse warming
The U.S. has never ratified the treaty
Treaty supporters argue:
Wealth not necessarily tied to fuel consumption
Curbing consumption and emissions could help the economy
Models show the longer we wait, the worse it will get
Consider the alternatives: runaway temperature changes, famine, global unrest.
The treaty expires in 2012 – the sequel is looking less than inspired.

56. Natural Causes of Climate Change
Astronomical
Tectonic
Position of the Continents
Volcanic Eruptions

57. Astronomical Causes – Sunspot cycles
The sun’s output varies over time - Local activity such as sunspots and solar storms has effect on solar output
Some studies show relationship between changes in global temperature and sunspot cycles, which change solar intensity by a minute amount.
This change in solar radiation may be responsible for a very small part of world temperature change.

58. Astronomical Causes – Milankovitch Cycles
These large-scale cycles (100,000, 41,000 and 26,000 respectively) are visible in the climate record and do not correspond to the rate of temperature change we see today.

59. Changes in seawater chemistry attributed to – Milankovitch Cycles
Changes in seawater chemistry which resulted in alternating layers of limestone and carbon-rich marl.
Many researchers say that these cycles have a small effect on world temperatures and are not responsible for recent changes

60. Tectonics and climate change
The position of the continents influences winds and ocean currents.
North and South America joined, separating Atlantic from Pacific in the tropics.
Current configuration of continents keeps Arctic Ocean landlocked.

61. Tectonics and climate change
200 mya, the single continent Pangea was near the south pole
Continental interiors tend to have more severe winters. For a single large landmass, even more so.
Influences winds and ocean currents

62. Volcanoes and climate change
Volcanoes emit ash, particulates and sulfur compounds, which block sunlight and so cool the atmosphere.
Volcanoes emit large quantities of CO2, which leads to warming of the atmosphere.

63. Possible Consequences of Global Warming
Sea-level changes – sea-level has risen markedly from 1900 to 2000
water expands when warm
Glacial (ice on land) melting is increasing
Effects on people
Tropical diseases flaring up in new areas
Population stress on food and water supplies as well as other global systems

64. Figure 21.16 Predicted consequences of global warming.
Fig , p.515

65. Thermohaline circulation – how global warming could cause global cooling or “the day after tomorrow”
Warmer sea surface temperature could slow or stop vertical currents
This would stop, or re-route the Gulf Stream, which would cool the Earth
Thermohaline currents have decreased 30% from

66. If the Labrador Current (Cold) is too fresh to sink, it may block passage of the N. Atlantic Drift (warm) which moderates the climate of Great Britain and Scandinavia
Figure Major ocean currents of the world.

67. Figure Some climate models indicate that warmer temperatures may shut off the Gulf Stream and North Atlantic drift, which could result in subsequent global cooling.
Fig a, p.519

68. Figure Some climate models indicate that warmer temperatures may shut off the Gulf Stream and North Atlantic drift, which could result in subsequent global cooling.
Fig b, p.519

69. Figure (A) Antarctica is surrounded by ice shelves, which are particularly extensive on the western edge of the continent. (B) About 5.3 million cubic kilometers of ice has broken free and floated into the ocean since the last ice age maximum about 20,000 years ago. The Ross Ice Shelf has retreated up to 900 km and retreat has accelerated in the past decade.
Fig ab, p.518

70. Figure (C) A complete collapse of the West Antarctic Ice Shelf would raise global sea level by five meters and drown low lying regions such as south Florida. Source: Ross Ice Shelf. Scientific American, Dec 2002, p. 101.
Fig c, p.518