Ch 4. The three modern global change problems.

1. Ch 4. The three modern global change problems.

2. Earth has been changing and will continue to do so. It is changing faster today than it ever has. The major reason is human activity. • Ozone depletion; Ozone hole in South Pole • deforestation; • Greenhouse gases and global warming

3. Ozone source: O and O2 makes it through chemical process. Location: in middle-layer atmosphere (stratosphere). roles: absorb ultraviolet radiation from Sun.

4. Vertical Structure of the Atmosphere 4 distinct layers determined by the change of temperature with height

5. Ozone depletion describes two distinct, but related observations: (1) a slow, steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere (ozone layer) since the late 1970s, (2) a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions during the same period.

6. Ozone ( ) is a form of oxygen, and protects the earth’s surface from Sun’s harmful ultraviolet radiation. Ozone depletion is the result of a complex set of circumstances and chemistry . Antarctic Ozone Levels in Fall 2003 The ozone hole is represented by the purple, red, burgundy, and gray areas that appeared over Antarctica in the fall of 2003. The ozone hole is defined as the area having less than 220 Dobson units (DU) of ozone in the overhead column (i.e., between the ground and space).

7. Image of the largest Antarctic ozone hole ever recorded (September 2006).

8. Ozone over Antarctic during Oct.

9. Mean total ozone over Antarctica during the month of October

10. It shows a sharp drop beginning in the early 1970s. The graph to the left shows long-term ozone levels over Arosa, Switzerland. Although ozone levels rise and fall in natural cycles, the average level remained constant from 1926 until 1973. Beginning in 1973, however, and continuing through 2001, ozone levels have dropped at a rate of 2.3 percent / decade.

11. Too much ultra-violet light can result in: • Skin cancer • Eye damage such as cataracts • Immune system damage • Reduction in phytoplankton in the oceans that forms the basis of all marine food chains including those in Antarctica. • Damage to the DNA in various life-forms. So far this has been as observed in Antarctic ice-fish that lack pigments to shield them from the ultra-violet light (they've never needed them before) • Probably other things too that we don't know about at the moment.

13. Global warming is the serious problem because: • It affects the greatest number of people • Migration of marine animals could result • Rising sea level could result • Cold climate species might die • Ozone depletion and deforestation are both confined to particular areas whereas global warming is truly global

14. Global warming is the serious problem because: • It affects the greatest number of people • Migration of marine animals could result • Rising sea level could result • Cold climate species might die • Ozone depletion and deforestation are both confined to particular areas whereas global warming is truly global

15. Why does a ozone hole form over Antarctica? The ozone hole is caused by the effect of pollutants in the atmosphere destroying stratospheric ozone. During the Antarctic winter something special happens to the Antarctic weather. • Firstly, strong winds blowing around the continent form, this is known as the "polar vortex" -  this isolates the air over Antarctica from the rest of the world. • Secondly, clouds form called Polar Stratospheric Clouds. Clouds turn out to have the effect of concentrating the pollutants that break down the ozone, so speeding the process up.

16. Deforestation

17. Deforestation affects Carbon balance Hydrological cycle Radiative energy balance Biodiversity

18. Statistics It has been estimated that about half of the earth's mature tropical forests — between 7.5 million and 8 million km2 of the original 15 million to 16 million km2 , have now been cleared since 1947. • North America and Europe – already done • 85% of old growth forests in US destroyed by settlers – most replanted • Parts of Pacific NW and Alaska – deforesting now as fast as Brazil Canada: One case of deforestation in Canada is happening in Ontario's boreal forests, near Thunder Bay, where 28.9% of a 19,000 km² of forest area had been lost in the last 5 years and is threatening woodland caribou. This is happening mostly to supply pulp for the facial tissue industry. In Canada, less than 8% of the boreal forest is protected from development and more than 50% has been allocated to logging companies for cutting.

19. Tropical Rainforest Earth's most complex biome in terms of both structure and species diversity; abundant precipitation and year round warmth. Climate: Mean monthly temperatures are above 64°F; precipitation is often in excess of 100 inches a year. Vegetation: 100 to 120 feet tall canopy. Soil: infertile, deeply weathered and severely leached. Red color because of high iron and aluminum oxides. Fauna: Animal life is highly diverse Distribution of biome: 10°N and 10°S latitude. Neotropical (Amazonia into Central America), African (Zaire Basin with an outlier in West Africa; also eastern Madagascar), Indo-Malaysian (west coast of India, southeast Asia)

20. Tropics • Rainforests 50 years ago covered 14% of the world's land surface and have been reduced to 6%,and that all tropical forests will be gone by the year 2090 • Brazil – slash and burn; Amazon – 200% increase in deforested area from 1979 - 1988 Some scientists have predicted that unless significant measures (such as seeking out and protecting old growth forests that have not been disturbed) are taken on a worldwide basis, by 2030 there will only be ten percent remaining.

21. The problem • Disappearing at a rate of tens of thousands of square miles per year • Land clearing in developing countries for farming and ranching (e.g., Brazil) • Wood as a fuel (e.g., 90% of Africans use wood as primary fuel) • Ballooning populations in developing countries • Loss of fauna associated with the forests • Current extinction rate of 50,000 species per year • Rate reflects fact that most fauna and flora in tropics are disappearing • Loss of soil value for farming (formation of laterites)

22. Effects • Lowered oxygen production levels • Increased CO2 • Changed climate (radiation, temperature) and hydrologic cycle • Loss of flora and fauna • Increased soil erosion (i.e., global erosion rate of 25.4 billion tons of top soil per year) • Increased effects of floods, especially coastal (e.g., 10x increase in catastrophic floods in Bangladesh) • Landslides • Cycle (vicious circle): • deforestation  soil erosion and loss of wood materials  lowered productivity of soil and loss of wood source  increased human needs  enhanced deforestation • e.g., 40-50 million trees removed in Haiti each year – correlates with 7x increase in food aid over last 20 years

23. Global warming

26. `The balance of evidence suggests that there is a discernible human influence on global climate' Intergovernmental Panel on Climate Change (United Nations), Second Assessment Report, 1996

27. `There is new and stronger evidence that most of the warming observed overthe last 50 years is attributable to human activity' Intergovernmental Panel on Climate Change (United Nations), Third Assessment Report, 2001

28. `Most of the observed increase in globally averaged temperatures since the mid-20th century is verylikely due to the observed increase in anthropogenic greenhouse gas concentrations’ Intergovernmental Panel on Climate Change (United Nations), Fourth Assessment Report, 2007

29. Joseph Fourier (1827) Recognized that gases in the atmosphere might trap the heat received from the Sun. James Tyndall (1859) Careful laboratory experiments demonstrated that several gases could trap infrared radiation. The most important was simple water vapor. Also effective was carbon dioxide, although in the atmosphere the gas is only a few parts in ten thousand. Svante Arrhenius (1896) Performed numerical calculations that suggested that doubling the amount of carbon dioxide in the atmosphere could raise global mean surface temperatures by 5-6°C. Guy Callender (1939) Argued that rising levels of carbon dioxide were responsible for measurable increases in Earth surface temperatures. Estimated that doubling the amount of CO2 in the atmosphere could raise global mean surface temperatures by 2°C. Discovery of the Greenhouse Effect

34. GREENHOUSE EFFECT? Glass allows visible radiation to pass through the glass which absorbs thermal radiation and re-emits some of it back into the greenhouse --- like a radiation blanket.

35. Heat Transfer --- Convection • Less dense warm air moves upward and more dense cold air moves downward. Convection is the dominant process for transferring heat in the troposphere.

36. The distribution of temperature in a convective atmos.(red line). The green line shows how the temperature increases when the amount of CO2 present in atmos. is increased (in the diagram the difference between the lines is exaggerated). Also shown for the two cases are the average levels from which thermal radiation leaving the atmosphere originates (about 6km for the unperturbed atmosphere).

37. Radiation is emitted out to space by these gases from level somewhere near the top of the atmos. – typically from between 5 and 10km high. Here, temperature is much colder -30 – 50C or so colder than at the surface. => emitting less radiation to space. So: absorb radiation emitted from the earth surface but then to emit much less radiation out to space.

38. Component of the radiation (in watts per square meter) which on average enter and leave the earth’s atmos. and make up the radiation budget for the atmosphere.

39. The enhanced greenhouse effect F = T4  = 5.67 x 10-8 W/m2/K4 average levels from which thermal radiation leaving the atmosphere originates

40. Blackbody rad. curves for Sun & Earth max = const./T Temp. T in K const. = 2898 m

46. Planetary energy balance • Earth is at steady state: Energy emitted by Earth = Energy absorbed ..(1) • E emitted = (area of Earth)   Te4 = 4 Re2   Te4 (Te= Earth’s effective rad. temp., Re= Earth’s radius) • E absorbed = E intercepted - E reflected • Solar E intercepted = S Re2 (solar flux S) • Solar E reflected = AS Re2 (albedo A) • E absorbed = (1-A) S Re2 • (1) => 4 Re2   Te4 = (1-A) S Re2

47. Magnitude of greenhouse effect •  Te4 = (1-A) S/4 • Te = [(1-A) S/(4  )]1/4 (i.e. fourth root) • Te = 255K = -18°C, very cold! • Observ. mean surf. temp. Ts = 288K = 15°C • Earth’s atm. acts as greenhouse, trapping outgoing rad. • Ts - Te = Tg, the greenhouse effect • Tg = 33°C

48. Greenhouse effect of a 1-layer atm. S/4 AS/4 Te4 Te Atm. Te4 (1-A)S/4 Ts4 Ts Earth • Energy balance at Earth’s surface: • Ts4 =(1-A)S/4 +Te4 ..(1) • Energy balance for atm.: • Ts4 = 2Te4 .. (2)

49. Subst. (2) into (1): Te4=(1-A)S/4 ..(3) (same eq. as in last lec.) Divide (2) by ; take 4th root: Ts= 21/4Te = 1.19 Te For Te = 255K, Ts = 303K. (Observ. Ts = 288K) Tg = Ts- Te = 48K, 15K higher than actual value. • Overestimation: atm. is not perfectly absorbing all IR rad. from Earth’s surface.

50. Weather forecasting also uses atm. GCMs. Assimilate observ. data into model. Advance model into future => forecasts. • Simpler: 1-D (vertical direction) radiative-convective model (RCM): Doubling atm. CO2 => +1.2°C in ave.sfc.T • Need to incorporate climate feedbacks: • water vapour feedback • snow & ice albedo feedback • IR flux/Temp. feedback • cloud feedback