Geological record of climate change

1. Geological record of climate change

2. Geological record of climate is fairly complete for the past 100,000 years • the record shows rapid climate change • Forcing factors and their time spans over which they could influence climate:

3. Three cycles in the changes in solar luminosity • 11-year sunspot cycle • 78-year Gleissbery cycle • 200-year sunspot cycle • Sunspots • dark areas on the Sun’s surface • colder than the surrounding area • 4,000 K (about 3,700° C) vs. 5,800 K (about 5,500° C) • causes cooling on Earth • Sunspots caused by changes in Sun’s magnetic field • Sunspots last from days to even months • number of Sunspots not always the same

4. Sunspots observed during a cycle of high sunspot activity, March 30, 2001 http://www.oneminuteastronomer.com/2009/09/11/sunspots/ E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our Energy Future, Columbia University Press. Source: SOHO/MDI Consortium

5. Variations in Earth’s orbit around the Sun has influence on Earth’s climate on a scale of tens of thousands to hundreds of thousands of years • Obliquity (tilt), Eccentricity, and Precession (wobble) • Obliquity • greater the tilt, the colder the winters and the hotter the summer • affects Northern Hemisphere much more than Southern Hemisphere because more land mass at the former

6. Eccentricity • affects distance of Earth to Sun, so alters total solar radiation received by Earth • nearer the Earth to the Sun, hotter • Precession • wobbling which causes the North Hemisphere to face closer to the Sun brings greater warming effect http://en.wikipedia.org/wiki/Axial_precession_(astronomy)

7. The Milankovitch cycles 21.5 to 24.5 current tilt E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our Energy Future, Columbia University Press. Source: R. Rohde, Global Warming Art

8. Variations in Earth’s orbit has much less effect on observed warming today than anthropogenic effects • without greenhouse gases, the variations in Earth’s orbit are actually causing global cooling • reducing climate forcing 0.035 Wm-2 per decade • with greenhouse gases, the climate forcing increases 0.2 Wm-2 per decade

9. Natural vs. anthropogenic forcing with human activities without human activities (natural forcing)

10. Climate record in Greenland ice • In 1989, two teams, one European and one American, begin drilling for ice cores in Greenland • In 1993, they obtained two complete drill cores through the entire ice sheet • American team drilled down to 3,053 meters • European team drilled down to 3,029 meters • These ice cores contained the continuous geological record of climate for the past 110,000 years

11. The location of Greenland Ice Sheet drill sites E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our Energy Future, Columbia University Press. Source: Geological Survey of Greenland

12. Greenland ice core E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our Energy Future, Columbia University Press. Source: NOAA

13. Ice forms as the snow laid down each year compacts and recrystallizes into ice during their burial by younger layers of snow • Newly fallen snow is porous and mixed with air • As the snow recrystallizes, some of the air is trapped to form bubbles in the ice • dust also accumulates, so the ice holds samples of ancient atmosphere and its dust • Greenland is the best place to obtain ice cores because of higher accumulation of snowfall in Greenland • 20 cm a year at Greenland • 2 cm a year at Antarctica

14. Annual layers in ice is determined by • variations in cloudiness which is caused by the differences in bubble and ice grain size • radiocarbon dating of entrapped CO2 • Calibration of age by comparing the date of a known event • such as high sulfuric acid content in a layer of the ice core with a known volcanic eruption date Annual layers of the Greenland ice core (1837 m depth) http://en.wikipedia.org/wiki/Dye_3

15. The site at Greenland was chosen for ice core drilling because • close to ice drainage divide (where ice flows in opposite directions) • less mixing of annual layers • bedrock is relatively flat • important because when ice flows, it folds and fractures, disrupting/mixing the annual layers

16. Ice cores • 18O (heavy isotope) and 16O (light isotope) • 18O is 0.2% of O2, the rest (99.8%) is 16O • When liquid water evaporates to vapour or when vapour condenses to liquid water, • 18O is enriched in the liquid and 16O is enriched in the vapour • As water-laden air flows northward and cools, it loses more and more of vapour as precipitation, so increasingly more 16O but increasingly less 18O in the air • In cool periods, ice formed in Greenland has more 16O than the ice formed during warm periods • air that provides the snow to Greenland loses more of its water before it reaches Greenland during cold periods than during warm periods

17. The concentration of Ca, Na, and Cl are also indicators of past climate • Ca is present mainly as carbonate and represents atmospheric dust • In cool periods, • the air circulation system scours dust from a wider land area, so more dust present in the air • air is drier, leading to more drier (arid) regions and more dust to be scoured by air • Na and Cl are from the ocean as sea salt • Both dust and sea salt reach Greenland in the late winter to early spring

18. Today The record of temperature in the Greenland ice cores E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our Energy Future, Columbia University Press. Data from Mayewski et al., 1997

19. The record of the Younger Dryas in the Greenland ice cores Years before present E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our Energy Future, Columbia University Press. Data from Mayewski and Bender, 1995

20. Santorini (?), Greece approx. 1627 B.C. The record of major volcanic eruptions in the Greenland ice cores E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our Energy Future, Columbia University Press. Data from Zielinski et al., 1994

21. Ocean sediments • Every year, 6-11 billion tons of sediment accumulate on the ocean floor • sediment consists of dead planktonic (near surface dwelling) and benthic (deep-water dwelling) • The marine sediment record is rather complete but burrowing organisms and ocean currents commonly disturb/mix the layers NOAA Image Gallery

22. Climate conditions can be deduced from the composition, abundance, and characteristics of the fossils in the sediment • 18O:16O ratio in the hard shells of sea-dwelling creatures • high ratio means high evaporation rates (leaving 18O behind in the sea), thus, indicating warm period • higher dust (from winds) content indicate cool periods • cool periods indicated by low humidity and stronger winds which scours more dust

23. Foraminifera, or forams, (protozoa) and diatoms (algae) are commonly used as microbial climate proxies • They are both planktonic (near surface-dwelling) or benthic (bottom- dwelling) creatures • Foram shells are made up of calcium carbonate (CaCO3) while diatom shells are composed of silicon dioxide (SiO2) • Their shell remains are taken from sediments and analyzed • warmer water tends to evaporate off more of the lighter isotopes (16O), so shells grown in warmer waters will be enriched in the heavier isotope (18O)

24. Diatoms http://starcentral.mbl.edu/microscope

25. Forams http://starcentral.mbl.edu/microscope/

26. The abundance of certain microorganisms is an indicator of sea surface temperature • determine the foram and diatom population dynamics • Relative abundance and species composition may indicate environmental conditions • Warmer weather will usually cause organisms to proliferate (population explosion) • Each species has a particular set of ideal growing conditions, so species composition (or combination) at a particular site at a particular time may indicate past environmental conditions

27. Lake sediments • Sediments in mid-latitudes lake • high carbonate contents correlate with extensive global ice volumes, reflecting low quantities of water entering the lake and more brackish (salty) lake water • low carbonate correlate with warm periods, when water level of lakes was high and the water fresher

28. Varves • alternating light and dark layers in sediment in lake valleys • In winter, lake surface is frozen, so no sediments enter water and microscopic organisms die from lack of light for photosynthesis. Fine clay still suspended in the lake will settle and accumulate at the lake bottom, producing a dark layer • In spring, sediments and nutrients (from runoff) enters the lake. The sediment settle and accumulate at the lake bottom as a light layer • Thickness of dark layers reflect summer biological activity/productivity • Thickness of light layers reflect the amount of meltwater entering the lake

29. Varves exposed on the campus of the University of Massachusetts, Amherst E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our Energy Future, Columbia University Press. Photograph by J. Beckett, American Museum of Natural History

30. Corals • Corals can be used to determine short term climate changes • Corals build skeletons by extracting Ca and carbonate from sea water • Corals formed during winter and summer have different densities • Ratio of 18O:16O reflect seawater temperature • Concentration of trace elements (such as Cd and Ba) can be analyzed to determine • upwelling and changes in windblown sediment or river runoff entering the ocean • high Cd and Ba indicate increased upwelling of water

31. Coral E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our Energy Future, Columbia University Press. Photograph by D. Finnin, American Museum of Natural History

32. Dendroclimatology • Each year, trees add a layer of growth between the older wood and the bark. This layer, or ring as seen in cross section, can be • wide = indicating a wet season (good growth) • narrow = indicating a dry growing season (poor growth) • Tree rings indicate good or bad growing seasons which reflect available moisture, temperature, and cloud cover • Limitations • past climate record not as long as ice cores • time span obtained so far is 11,000 years of climate record • tree growth is sensitive to local growing conditions • may not represent global climate at that time

33. Cross section of a tree trunk being prepared E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our Energy Future, Columbia University Press. Photograph by R. Mickens, American Museum of Natural History

34. http://www.priweb.org/globalchange/climatechange/studyingcc/scc_01.htmlhttp://www.priweb.org/globalchange/climatechange/studyingcc/scc_01.html http://www.beringia.com/climate/content/treerings.shtml

35. Stomata • Plant fossils from buried sediments are a relatively new tool being used to unravel Earth's carbon dioxide (CO2) history • Stomata are tiny pores on plant leaves which regulate carbon dioxide absorption and water vapor release • for photosynthesis (inhale CO2, exhale O2) • Lesser number of stomata indicative of high atmospheric CO2, and greater when atmospheric CO2 is low http://evolution.berkeley.edu/evolibrary/article/0_0_0/mcelwain_03

36. An illustration of the stomatal CO2 proxy. (Left) Photomicrograph of fossil leaf cuticle of the fern. (Right) The fern's nearest living relative, Stenochlaena palustris The stomatal index of the fossil cuticle is considerably lower than the extant cuticle, indicating that CO2 was higher directly after the K/T boundary than today. Photos courtesy of Barry Lomax (University of Sheffield, Sheffield, U.K.) (Scale bars, 10 μm)‏ Royer D L PNAS 2008;105:407-408

37. Stomatal Index, SI (%) = 100 x NS / (NS + EC) where NS is the number of stomata and EC is the number of epidermal cells Ph.D. dissertation of Tom van Hoof: "Coupling between atmospheric CO2 and temperature during the onset of the Little Ice Age“; http://igitur-archive.library.uu.nl/dissertations/2004-1214-121238/index.htm

38. Climate change : the science, impacts and solutions. 2nd edn. A. Barrie Pittock, CSIRO, Australia, 2009

39. Past climate • Using proxy data, Mann et al. (1998) reconstructed the climate for the past 1000 years • known as the famous “hockey stick” graph Mann ME, Bradley RS, Hughes MK (1998) Global-scale temperature patterns and climate forcing over the past six centuries. Nature 392:779–787. http://www.guardian.co.uk/environment/2010/feb/02/hockey-stick-graph-climate-change

40. Instrumental Temperature Record http://en.wikipedia.org/wiki/Temperature_record_of_the_past_1000_years

42. Richter, B. 2010. Beyond Smoke and Mirrors: Climate Change and Energy in the 21st Century. Cambridge University Press, New York

43. http://motls.blogspot.com/2006/07/carbon-dioxide-and-temperatures-ice.htmlhttp://motls.blogspot.com/2006/07/carbon-dioxide-and-temperatures-ice.html

44. The Antarctic temperature starts to change first, followed by CO2 • responds between 800- and 1000-year lag • Why CO2 lags temperature? • Oceans are large, and it simply takes centuries for them to warm up or cool down before they release or absorb gases • warm oceans hold CO2 lesser than cold oceans • so warming ocean releases CO2 slowly and gradually • this is why even if no more antropogenic CO2 is released today, the Earth will still warm because of “past CO2” being gradually released by the oceans

45. Climate tipping points World Development Report 2010: Development and Climate Change, The World Bank, Washington, 2010