Climate Change: Past and Future ERTH 303, 3 December, 2009

Transcription

1 Climate Change: Past and Future ERTH 303, 3 December, 2009 a) Defining climate change b) Patterns of past climate change c) Causes of past climate change temperature relative to means ( ); 2006 ranks as the 6 th warmest year since 1880 (

2 (b) Patterns of Past Climate Change Sea Level Rise ~ 3.5 mm/yr mm Higher than predicted ( rates were 1.8 mm yr) IPCC 4 th Assessment, Fig. 6.3:

3 (b) Patterns of Past Climate Change Temperature~ 0.76 C IPCC 4 th Assessment, Fig. 6.3:

4 (b) Patterns of Past Climate Change Warm and cool periods strongly linked to levels of CO 2 IPCC 4 th Assessment, Fig. 6.3:

5 (b) Patterns of Past Climate Change Warm and cool periods strongly linked to levels of CO 2 CO2 levels = ppm Today? Future? IPCC 4 th Assessment, Fig. 6.3:

6 (b) Patterns of Past Climate Change Climate varies at multiple scales Multi-millennial millennial: glacial / interglacial periods IPCC 4 th Assessment, Fig. 6.3:

7 (b) Patterns of Past Climate Change Glacial-Holocene l l transition Younger Dryas (YD; 13,000-11,800 yr ago) Abrupt cooling, lasting 1200 yr Mechanism: change in salinity and shutdown of North ot Atlantic ta tcocean circulation

8 (b) Patterns of Past Climate Change Medieval Warm Period ( Medieval Climate Anomaly ) AD: Viking settlement of Greenland IPCC 4 th Assessment, Fig. 6.13: AD

9 (b) Patterns of Past Climate Change Little Ice Age AD: local temp. of C IPCC 4 th Assessment, Fig. 6.13: AD

10 (b) Patterns of Past Climate Change 20 th century warming > 0.8 C globally (from instrumental record) IPCC 4 th Assessment, Fig. 6.13: AD

11 Climate Change: Past and Future ERTH 303, 1 December, 2009 a) Defining climate change b) Patterns of past climate change c) Causes of past climate change temperature relative to means ( ); 2006 ranks as the 6 th warmest year since 1880 (

12 (c) Causes of Past Climate Change Mechanisms: Millennial time scale, global spatial scales: 1. Changes in Earth s orbital parameters 2. Changes in land configuration 3. Feedbacks Annual to centennial time scales, local to global spatial scales: 1. Variations in solar output t (e.g., sunspots) 2. Changes in atmospheric aerosols 3. Changes in radiation-absorbing bi gasses 4. Feedbacks

13 (c) Causes of Past Climate Change 1. Changes in Earth s orbital parameters Milankovitch Cycles: Changes Sun-Earth geometry that alter the distribution of insolation over millennial time scales; caused by changes in: a. Eccentricity b. Obliquity c. Precession (of the equinox)

14 (c) Causes of Past Climate Change Eccentricity: it Changes in Earth s orbit, over a 100,000- and 400,000-yr cycle, 1-11% difference in Earth-Sun distance (compared to 3% today).

15 (c) Causes of Past Climate Change Obliquity: it Changes in Earth s axial tilt, over 41,000- yr cycle; varies between ; 15% variation in available solar radiation in high latitudes.

16 (c) Causes of Past Climate Change P i ( f th i ) W bbl f E th Precession (of the equinox): Wobble of Earth s axis over 27,000-yr cycle, so poles point in different direcitons.

17 (c) Causes of Past Climate Change P i ( f th i ) Precession (of the equinox): Interacts with eccentricity

18 (a) Causes of Past Climate Change Net effect of eccentricity, it obliquity, it and precession: present past IPCC 4 th Assessment, Chap. 6, FAQ 6.1: ; 18

19 (a) Causes of Past Climate Change Mechanisms: Millennial time scale, global spatial scales: 2. Changes in land configuration Distribution of continents Mountain building: e.g. Rockies, Himalayas, and Andes modify Rossby waves during winter and promote monsoon circulation in the summer. 19

20 (c) Causes of Past Climate Change M h Mechanisms: Millennial time scale, global spatial scales: 3. Feedbacks: Ice-albedo feedbacks

21 (a) Causes of Past Climate Change Mechanisms: Annual to centennial time scales, local to global spatial scales: 1. Variations in solar output (e.g., sunspots) % change in Sun s output; 11-yr cycles Maunder Minimum 21

22 (a) Causes of Past Climate Change Variations in solar output: t Maunder Minimum, i minimal sunspot activity between , coincident with the Little Ice Age. IPCC 4 th Assessment, Fig. 6.13: Textbook Fig., pg

23 (a) Causes of Past Climate Change Mechanisms: 2. Changes in atmospheric aerosols: absorb incoming solar radiation, heating the atmosphere increase backscattering and reduce radiation reaching the surface increase absorption of outgoing, longwave radiation and increase nighttime temperatures t lead to more extensive, longer-lived, brighter clouds 23

24 (a) Causes of Past Climate Change Aerosols can lead to more extensive, longer-lived, brighter clouds: e.g., stratocumulus clouds from ship exhaust (e.g. aerosols) Textbook Fig., pg

25 (a) Causes of Past Climate Change Greenhouse gases can destroy and enhance aerosols Result = warming/cooling Science News Nov

26 (a) Causes of Past Climate Change Greenhouse gases can destroy and enhance aerosols Result = warming/cooling Science News Nov

27 (a) Causes of Past Climate Change 2. Changes in atmospheric aerosols can Tropospheric aerosols: sea salt, soot and gasses from fires, windblown dust, and more short residence times hours to days so their effects vary widely across space and are short lived NET EFFECT = reduce surface temperatures globally Thus, increased tropospheric aerosols have reduced the magnitude of greenhouse-gas induced d warming 27

28 (a) Causes of Past Climate Change 2. Changes in atmospheric aerosols can Stratospheric aerosols: volcanic eruptions (sulfur gases) longer residence time (weeks to months) NET EFFECT = promote globally ll lower temperatures e.g. El Chichon (1982), Mt. Pinatubo (1991) Textbook Fig., pg

29 (a) Causes of Past Climate Change Global l aerosol content t before and after Mt. Pinatubo: June 12, 1991 high content low content 29 Textbook Fig., 16-10

30 (a) Causes of Past Climate Change Annual to centennial time scales, local l to global spatial scales: 3. Changes in radiationabsorbing (aka greenhouse ) gasses CO 2, CH 4, N 2 Oall are effective absorbers of longwave radiation, thus warm Earth s climate. IPCC 4 th Assessment, Chapter 2: 30

31 (a) Causes of Past Climate Change Summary: 1. Obit Orbital parameters 2. Land configuration 3. Solar output 4. Atmospheric aerosols 5. Concentration of greenhouse gasses IPCC 4 th Assessment, Chapter 2: 31

32 (a) Causes of Past Climate Change Feedbacks: Positive feedbacks: amplify a change ice-albedo feedbacks i. temperatures ii. sea/land ice iii. albedo iv. temperatures 32 Textbook Fig., 16-12

33 (a) Causes of Past Climate Change Feedbacks: 33

34 (a) Causes of Past Climate Change Feedbacks: Positive feedbacks: amplify a change evaporation of water vapor i. CO 2 ii. temperatures iii. evaporation iv. increased water vapor, low clouds v. temperatures * Models suggest ½ current warming is due to increased water vapor! 34

35 (a) Causes of Past Climate Change Feedbacks: Positive feedbacks: amplify a change atmosphere-plant interactions i. temp., CO2 ii. dark veg. iii. albedo iv. temperatures Tundra vegetation (left) has a lower albedo than boreal forest Vegetation (right). Replacing light with dark vegetation can alter energy budgets and lead to overall warming. 35 Brooks Range, Alaska.

36 (a) Causes of Past Climate Change Feedbacks: Negative feedbacks: self-regulation Another side of the water vapor feedback i. temperatures ii. evaporation, water vapor, low clouds iii. albedo iv. temperatures 36

37 (a) Causes of Past Climate Change Feedbacks: Negative feedbacks: self-regulation ocean-atmosphere interactions involving thermohaline circulation: 37

38 (a) Causes of Past Climate Change Feedbacks: Negative feedbacks: self-regulation ocean-atmosphere interactions involving thermohaline circulation: i. temperatures ii. melting of ice (adding freshwater to ocean) iii. thermohaline circulation iv. temperaturest 38

39 16.01 The stratocumulus clouds show the presence of ships because the ships expel. 1. water vapor 2. clouds 3. smog 4. aerosols 39

40 16.01 The stratocumulus clouds show the presence of ships because the ships expel. 1. water vapor 2. clouds 3. smog 4. aerosols 40

41 16.05 During the most recent glacial maximum, the southernmost margin was at. 1. A A B 2. B 3. C 4. D C D Courtesy, CIA 41

42 16.05 During the most recent glacial maximum, the southernmost margin was at. 1. A A B 2. B 3. C 4. D C D Courtesy, CIA 42

43 16.07 The figure shows Earth s s. 1. eccentricity 2. obliquity 3. quasi-biannual oscillation 4. precession 43

44 16.07 The figure shows Earth s s. 1. eccentricity 2. obliquity 3. quasi-biannual oscillation 4. precession 44

45 16.08 The images show aerosols prior to and after the 1991 eruption of Mount. 1. Fuji 2. Shasta 3. Pinatubo 4. Rainier 45

46 16.08 The images show aerosols prior to and after the 1991 eruption of Mount. 1. Fuji 2. Shasta 3. Pinatubo 4. Rainier 46

47 16.15 The arrow on these temperature reconstructions shows a cool period known as the. 1. Younger Dryas 2. African Humid Period 3. Little Ice Age 4. Interglacial 47

48 16.15 The arrow on these temperature reconstructions shows a cool period known as the. 1. Younger Dryas 2. African Humid Period 3. Little Ice Age 4. Interglacial 48