1. Ch 23. Global Climate Change Fig. 23.3 Fig. 23.9

2. Greenhouse effect Sunlight enters the atmosphere Radiation is backscattered in the form of longer wavelength radiation (infrared). Atmosphere works like the lid of a greenhouse. The more greenhouse gases, the more this heat radiation is trapped in the atmosphere, warming air and Earth’s surface. See Fig. 23.6

3. Effect of greenhouse gases  Without greenhouse gases, earth’s mean temperature would be 33°C colder (today’s mean temp of 15°C compared to -18°C).  In earth’s climatic history, cold (glacial) and warm (interglacials) stages have always been accompanied by low (180 ppmv) and high (280 ppmv) CO 2 levels, respectively.

4. Anthropogenic gases that contribute to the greenhouse effect Greenhouse GasRelative contribution Carbon dioxide (CO 2 )60% Methane (CH 4 )15% Nitrous oxide (N 2 O)5% Tropospheric ozone (O 3 )8% CFC-114% CFC-128%

5. Carbon dioxide is increasing in the atmosphere As a result of human activities, carbon dioxide in the atmosphere has increased by 30% since 200 years ago

6. Reasons for the rise in greenhouse gases:  Burning of fossil fuels (oil, coal and natural gas) release 5.5 Gt of carbon into the atmosphere per year  1.6 Gt C is released due to slash and burn practices in tropical rain forests. See Fig. 23.8

7. The anthropogenic carbon budget 1980-89 (IPCC, 1995) (Units are GtC/yr; uncertainties are 95% Confidence Limits) Carbon Dioxide Sources (1) Emissions from fossil fuel combustion and cement production: 5.5 ± 0.5 (2) Net emissions from changes in tropical land use: 1.6 ± 1.0 (3) Total anthropogenic emissions [(1)+(2)]: 7.1 ± 1.1 Partitioning Among Reservoirs (4) Storage in the atmosphere: 3.3 ± 0.2 (5) Ocean uptake: 2.0 ± 0.8 (6) Uptake by Northern Hemisphere forest regrowth: 0.5 ± 0.5 (7) Inferred sink [(3)- {(4)+(5)+(6)}]: 1.3 ± 1.5

8.  75% of CO 2 is emitted by 25% of industrialized world population.

9. Earth’s average temperature is rising Earth’s average surface temperature has risen at least 0.6°C (1.1°F) in the last 130 years

10.  Projection for global temperature rise until 2100: 1.4-5.8 °C (2.5-10.4 F) according to different climate Models (see Fig. 23.17) 6 5 4 3 2 1 0

11.  Projection for global temperature rise until 2100: 1.4-5.8 °C (2.5-10.4 F) according to different climate Models (see Fig. 23.17)

12. Drilling of ice cores Climate is recorded in ice cores What about CO 2 changes in the past?

13. Drilling at Vostok (Antarctica)  Warming and cooling phases in earth’s history were always accompanied by CO 2 changes.  But at least during the last 400,000 years have CO 2 levels not been as high as today. Data from an ice core CO 2 in Earth’s climate history

14. Predicted changes with increased greenhouse warming Higher than normal sea surface temperatures that affect world climate Melting of polar ice caps and glaciers Increase in sea-level (coastal erosion, inundation, high coast protecting coastal communities) More severe droughts (in subtropics) and increased precipitation in higher latitudes Changes in water supply, quality, increased competition for water Longer and more intense heat waves Shifts in ecological zones (distribution of plants and animals, change in forests) Change in crop yields, irrigation needs See Table 23.1

15. Global sea level rise due to global warming  50 cm until 2100 (avg.), range: 20-96 cm  57% due to thermal expansion  33% due to glaciers/ice caps melting

16. Fig. 23.18 Melting of the north polar ice cap.

18. Where does the CO 2 go?

19. Uptake mechanisms of CO 2 by the ocean  The physical pump: Cold water that is saturated with CO 2 sinks from high latitudes (mainly North Atlantic, Antarctica) to form deep water. This water is removed from contact with the atmosphere for hundreds of years.  Biological carbon pump is the particulate or dissolved organic carbon that is produced in the photosynthetic zone and ‘exported’ to deeper water layers and finally buried in the sediment. About 10% leaves the mixed layer and is called Export Production. This carbon is removed from contact with the atmosphere for 100s of years. Only about 0.1 % of what is produced in the surface reaches the sediment and is permanently buried (on geological time- scales).

20. Atlantic Ocean subsurface water masses North Atlantic Central Water

21. Conveyer-belt circulation What happens if global conveyor is turned off? See Fig. 16.28

22. A ‘switching off’ of the global conveyor belt could cause a sudden cooling of higher latitudes and may have been responsible for the cooling event of the Younger Dryas.

23. Biological Carbon Pump

24. Ch 23. Global Climate Change Geology and climate Continental drift (Plate tectonics) may cause continental masses to move over poles and cause build-up of ice shields, increasing Earth’s albedo. Increased albedo exerts a positive feedback on climate cooling (i.e. enhances cooling) by decreasing the energy earth’s surface receives from the sun. Melting of ice sheets due to global warming has the opposite effect effect, decreasing albedo, and reinforcing global warming by increasing the solar energy hitting Earth’s surface.

25. Ch 23. Global Climate Change Geology and climate Plate tectonics also cause changes of ocean currents, i.e. of continents block warm ocean currents to reach higher latitudes, heat flux is diminished, temperature differences between low and high latitudes increase. Pols cool leading to a formation of ice caps and climate worldwide cools (increased albedo will further amplify this effect).

26. Ch 23. Global Climate Change Geology and climate Tectonic uplift (such as of the Himalayas and the Tibetan Plateau) might have increased weathering rates, which subsequently consumed CO 2 from the atmosphere, contributing to cooling and onset of glaciations in the Pleistocene.

27. Ch 23. Global Climate Change Geology and climate Volcanic eruptions can temporarily cause cooling bblocking solar radiation from entering atmosphere, but in the longer term are as source of CO 2 and contribute to greenhouse gas blanket enveloping Earth (increased volcanic outgassing might have ended the global glaciation event of the “Snowball Earth”, see Ch. 16).

28. Some conclusions... Atmospheric CO 2 levels are rising to levels unprecedented in recent climate history. This greenhouse gas causes global warming and a rise in sea level. The oceans mediate the atmospheric CO 2 increase by the action of the physical and biological carbon pump, which absorb about one third of fossil fuel CO 2. Both are in turn subject to climate change. On long time-scales (>10,000 years) interaction of lithosphere with cryosphere, hydrosphere and atmosphere) have driven climate on Earth. That is, until man arrived….

29. Some MCs... Which of the following is the current warm interglacial period? A. Holocene B. Miocene C. Paleocene D. Pleistocene

30. Some MCs... Based on ice core data, how rapidly can Earth shift from glacial to interglacial temperatures? A. 10 to 30 years B. 100 to 300 years C. 1000 to 3000 years D. 10,000 to 30,000 years

31. Some MCs... How much did the average surface temperature increase during the twentieth century? A. approximately 0.3 °C B. approximately 0.6 °C C. approximately 1.2 °C D. approximately 2.4 °C

32. Some MCs... Which of the following processes removes carbon from the atmosphere? A. photosynthesis B. respiration C. volcanism D. all of the above

33. Some MCs... What proportion of the total amount of carbon dioxide emitted into the atmosphere each year stays in the atmosphere? A. approximately 25% B. approximately 50% C. approximately 75% D. approximately 100%

34. Some MCs... Which of the following has dramatically changed the carbon cycle over the past 150 years? A. burial of organic carbon B. burning of fossil fuels C. deposition of carbon-rich sediments D. volcanism

35. Some MCs... By the end of the next century temperatures are predicted to rise ________ because of global warming. A. less than 1.5 °C B. 1.5 to 6 °C C. 6 to 20 °C D. greater than 20 °C

36. Some MCs... Over the next century the warming and expanding of oceans due to global warming would result in a rise in sea level of as much as ____________. A. 90 centimeters B. 9 meters C. 90 meters D. 900 meters

37. Some MCs... If all human activities that generated carbon dioxide were to stop, how long would it take for atmospheric carbon dioxide to return to its preindustrial level? A. 2 months B. 2 years C. 20 years D. 200 years

38. Some MCs... How has the concentration of carbon dioxide in the atmosphere changed since the start of the Industrial Revolution? A. Carbon dioxide concentrations have increased 3%. B. Carbon dioxide concentrations have increased 10%. C. Carbon dioxide concentrations have increased 30%. D. Carbon dioxide concentrations have increased 100%.

39. Some MCs... If Earth’s atmosphere did not contain greenhouse gases, the Earth’s surface would be __________. A. approximately 33 °C cooler B. approximately 10 °C cooler C. approximately 10 °C warmer D. approximately 33 °C warmer

40. Some MCs... The greenhouse effect is caused by __________. A. carbon dioxide and water vapor that trap heat radiating from the Earth’s surface B. heating of homes and businesses, which releases excess heat into the atmosphere C. oceans that trap heat radiating from the Earth's seafloors D. too many plants on the surface of the Earth, which prevent cooling of the surface

41. Some MCs... Chemical analysis of ice cores demonstrates that as temperature increases, concentrations of atmospheric __________. A. carbon dioxide and methane both decrease B. carbon dioxide decreases while methane increases C. carbon dioxide increases while methane decreases D. carbon dioxide and methane both increase