Climate change I: climate trends

1. Climate change I:climate trends Bio 415/615

2. Questions 1. How much colder was the Earth during the last glacial maximum? 2. What are Milankovitch cycles? 3. How do we know the Earth is warming? 4. Why do scientists believe the warming is anthropogenic? 5. How does the greenhouse effect work?

3. BE SKEPTICAL • Don’t take anything at face value! • Earth science is complicated • Believe good data and well constructed empirical models • Remember Nero’s Dilemma: ‘science not yet good enough’ is usually not a legitimate policy position

4. Last 500 my: delta O18 in fossils Plate tectonics? Solar system properties? Veizer et al. (1999)

5. Why delta O18? • O18 is a stable isotope of O16, created in supernovae • water that evaporates and forms clouds is enriched in the lighter form of oxygen (O16) • glaciers are thus made out of relatively more O16, while the oceans are enriched in O18 • oxygen in sea shells in marine cores (e.g., CaCO3) can be sampled in the lab for relative abundance of each isotope, compared to a standard • tells how much water globally was in ice versus oceans • can perform same technique with hydrogen isotopes

6. Last 65 my: delta O18 in benthic marine fossils Last 3 mya: closing of isthmus of Panama Zachos et al. (2001)

7. Last 5 my: delta O18 in benthic marine fossils Shows Milankovitch cycles of 100 and 41 kyr Lisiecki and Raymo 2005

8. Milankovitch cycles • Earth’s movement goes through cycles that affect its climate • Named after one of its discoverers, Milutin Milankovic (Serbian engineer) • Explain 100,000-yr ice ages (glaciation cycles) • Not accepted until data were available to test it (late 1970s)

9. Milankovitch cycles 100,000 yr cycle: the earth’s orbit gets more or less circular 41,000 yr cycle: the earth’s orbit gets more or less tilted ~20,000 yr cycle: the earth’s tilt changes WHEN hemispheres ‘look away’ from sun

10. Last 450,000 yrs: deltaD samples in 2 Antarctic ice cores Shows glaciation cycles of about 100,000 yrs Northern Hemisphere was about 5 C colder (between 3 and 7 C, depending on dataset and region) at the last glacial maximum Petit et al. 1999

11. Last 12,000 yrs: multiple sources Sources include deltaD from polar ice cores, tropical ocean sediment cores, mountain glacier ice core (Kilimanjaro), extrapolations from pollen records Rohde 2008 (online)

12. Last 150 yrs: instrumental records UK met office

13. Recent compared to 1940-1980 mean NASA

14. Pleistocene: ice ages • The Pleistocene describes the first epoch of the Quaternary Period (our glacial age): 2 mya-10,000 years ago • The Holocene describes the last 10,000 years (human expansion), a relatively warm period (interglacial) • An ice age cycle last about 100,000 years, with relatively short interglacials (~ 20,000 years)

15. What happened as the climate warmed? • Why is this a significant question for conservation biology?

16. How do we know what happened to plants and animals? • Plants: fossils (e.g., cones, wood) and pollen (palynology) • Animals: fossils • All: genetics! Scots pine

17. Pollen diagrams Shows relative abundance of different pollen types in a lake sediment core. Core depths are aged by radiocarbon dating of macrofossils.

18. Vegetation shifts Margaret Davis, 1983 Species moved independently of one another. Moreover, the character of communities was constantly changing:many of the these communities have no modern analogue.

19. from McLachlan et al. 2005 New evidence for periglacial survival?

20. Is the world warming? Figure 3.1. Annual anomalies of global land-surface air temperature (°C), 1850 to 2005, relative to the 1961 to 1990 mean for CRUTEM3 updated from Brohan et al. (2006). The smooth curves show decadal variations (see Appendix 3.A). The black curve from CRUTEM3 is compared with those from NCDC (Smithand Reynolds, 2005; blue), GISS (Hansen et al., 2001; red) and Lugina et al. (2005; green). IPCC 2007

21. Is the world warming? “Comparison of measured sea surface temperatures in the Western Pacific with paleoclimate data suggests that this critical ocean region, and probably the planet as a whole, is approximately as warm now as at the Holocene maximum and within 1°C of the maximum temperature of the past million years.” Hansen et al. 2006, PNAS “Global warming was 0.7°C between the late 19th century (the earliest time at which global mean temperature can be accurately defined) and 2000, and continued warming in the first half decade of the 21st century is consistent with the recent rate of 0.2°C per decade.” Hansen et al. 2006

22. Are humans causing warming? Intergovernmental Panel on Climate Change, Fourth Assessment Report, Summary for Policymakers, 2007.

23. Are humans causing warming? IPCC 2007 • YES. THE ARGUMENT: • Carbon dioxide and methane are the most powerful anthropogenic greenhouse gases and significantly influence global temperatures. • CO2 and CH4 concentrations in the atmosphere are higher than at any time over the last 650,000 yrs. • CO2 and CH4 concentrations have increased largely due to fossil fuel burning (and agriculture), with rates of increase unprecedented for over 10,000 yrs.

24. BUT… Humans also cool the atmosphere, by putting aerosols in the air (small particles that block incoming radiation) and changing surface albedo (reflectance of solar radiation). But cooling effects are strongly outweighed by warming factors. IPCC 2007

25. Keeling curve: CO2 on the rise Before 1900, CO2 concentration was 275-285 ppm

26. CO2 during the recent Pleistocene From ice cores

27. Future of CO2 depends on emissions Marland et al. 2003

28. Greenhouse effect Think in terms of input and output of the Earth’s energy (radiation): • Solar radiation heats the Earth. • Earth loses heat through longwave (infrared) radiation (so do you by standing in front of a window… every body not at absolute zero emits this radiation). • Some gases in Earth’s atmosphere BLOCK longwave radiation due to their chemical properties. This energy thus gets ‘trapped’ inside the atmosphere, and changes the Earth’s radiation balance. • (This is NOT what happens in a greenhouse.)

29. Greenhouse effect

30. Greenhouse gaseswithout them, Earth would be uninhabitable (think Mars);too much of them also a problem (think Venus) • Water vapor: accounts for 1/3 to 2/3 of the greenhouse effect, but is relatively constant and not generally anthropogenic • Carbon dioxide: accounts for 1/10 to ¼ of greenhouse effect; is sequestered by biomass, oceans, soils, and within the Earth’s crust, and released by burning biomass, soils, and fossil fuels • Methane: a potent greenhouse gas but relatively rare, emitted by anaerobic microbes in wetlands, less than 1/10 of greenhouse effect • Ozone, nitrous oxide, CFCs: produced mostly as products or byproducts of industry • Most of the atmosphere is N2 and O2; these are NOT greenhouse gases (they neither emit nor absorb longwave radiation)

31. Carbon cycle The amount of carbon (CO2) in the atmosphere depends on how much is sequestered in plants, soils, the ocean, and rocks. Sometimes dead plant material does not decompose and is buried and transformed by heat and pressure underground, forming carbon-rich ‘fields’ of coal, oil, and gas (fossil fuels). Humans burns these fuels and put C back into the atmosphere.

32. No end in sight to fossil fuel burning? globalwarmingart.com

33. Have humans influenced climate since before industrialization? Methane: 5,000 yr anomaly? CO2: 8,000 yr anomaly? Ruddiman 2003

34. How fast will the world warm? • General Circulation Models (GCMs) achieved widespread acceptance in 1990s for the ocean (OGCMs) and atmosphere (AGCMs); a ‘full’ climate model is now an ‘AOGCM’ • Model fluids in 3D across ‘cells’ over the Earth • Includes physical properties like pressure, velocity, temperature • Land surface properties like albedo and hydrology • Atmospheric properties like cloud cover and water vapor, air chemistry • Significant sources of uncertainty remain: e.g., clouds (can both cool and warm)

35. Models are stochastic! Figure 10.1.Several steps from emissions to climate response contribute to the overall uncertainty of a climate model projection. These uncertainties can be quantified through a combined effort of observation, process understanding, a hierarchy of climate models, and ensemble simulations. In a comprehensive climate model, physical and chemical representations of processes permit a consistent quantification of uncertainty. Note that the uncertainty associated with the future emission path is of an entirely different nature and not addressed in Chapter 10. Bottom row adapted from Figure 10.26, A1B scenario, for illustration only. IPCC 2007

36. Models must predict what the future world will look like, in terms of population size, economic growth, and what energy economies will use. These 3 emissions scenarios vary in energy efficiency, rate of tech advancement, extent of globalization, etc. Figure 10.8.Multi-model mean of annual mean surface warming (surface air temperature change, °C) for the scenarios B1 (top), A1B (middle) and A2 (bottom), and three time periods, 2011 to 2030 (left), 2046 to 2065 (middle) and 2080 to 2099 (right). Stippling is omitted for clarity (see text). Anomalies are relative to the average of the period 1980 to 1999. Results for individual models can be seen in the Supplementary Material for this chapter.

37. Clearly, warming over the next century depends on how the global economy develops in relation to new technologies that do not involve fossil fuels. Most agree at least 3 C warming is inevitable, and perhaps as high as 7 C. IPCC 2007 Figure 10.29.Projections and uncertainties for global mean temperature increase in 2090 to 2099 (relative to the 1980 to 1999 average) for the six SRES marker scenarios. The AOGCM means and the uncertainty ranges of the mean –40% to +60% are shown as black horizontal solid lines and grey bars, respectively. For comparison, results are shown for the individual models (red dots) of the multi-model AOGCM ensemble for B1, A1B and A2, with a mean and 5 to 95% range (red line and circle) from a fitted normal distribution.

38. Water predictions Changes in precipitation are more difficult to predict. A warmer atmosphere holds more water, but this means different things in different places. IPCC 2007 Figure 10.12. Multi-model mean changes in (a) precipitation (mm day–1), (b) soil moisture content (%), (c) runoff (mm day–1) and (d) evaporation (mm day–1). To indicate consistency in the sign of change, regions are stippled where at least 80% of models agree on the sign of the mean change. Changes are annual means for the SRES A1B scenario for the period 2080 to 2099 relative to 1980 to 1999. Soil moisture and runoff changes are shown at land points with valid data from at least 10 models.

39. Water predictions Models agree that more water in the atmosphere means larger precipitation events—this makes rainstorms stronger, and days between rain longer. IPCC 2007

40. Warming side-effects: drought FAQ 3.2, Figure 1. The most important spatial pattern (top) of the monthly Palmer Drought Severity Index (PDSI) for 1900 to 2002. The PDSI is a prominent index of drought and measures the cumulative deficit (relative to local mean conditions) in surface land moisture by incorporating previous precipitation and estimates of moisture drawn into the atmosphere (based on atmospheric temperatures) into a hydrological accounting system. The lower panel shows how the sign and strength of this pattern has changed since 1900. Red and orange areas are drier (wetter) than average and blue and green areas are wetter (drier) than average when the values shown in the lower plot are positive (negative). The smooth black curve shows decadal variations. The time series approximately corresponds to a trend, and this pattern and its variations account for 67% of the linear trend of PDSI from 1900 to 2002 over the global land area. It therefore features widespread increasing African drought, especially in the Sahel, for instance. Note also the wetter areas, especially in eastern North and South America and northern Eurasia. Adapted from Dai et al. (2004b). IPCC 2007

41. Changes that will directly influence plants and animals Mean temperature itself may influence plants and animals in the future, but more relevant might be the length of growing seasons and high temperature extremes. Both are on the increase. IPCC 2007

42. Warming side-effects: sea level Sea level has risen about 18 cm since 1880, as measured by tidal gauges in 23 sites around the world (Douglas 1997). Sea level rises from land glacier melting AND thermal expansion. These projections are from the IPCC 2001 report; newer data suggest the higher end curves are more reasonable. globalwarmingart.com

43. Warming side-effects: glaciers Mountain glaciers are generally thinning out at a rapid pace, many over 1 m/yr. 83% of all glaciers are thinning. Those in Scandinavia are stable or increasing. These are two glaciers in Glacier Bay National Park, Alaska. Dyurgerov and Meier 2005; globalwarmingart.com