Ice Cores, Climate Change, and Polar See-saws

1. USNC INQUA AMQUA NAGT/DLESE “On the Cutting Edge” Teaching Climate Change with Ice Core Data, celebrating IPY, June 2, 2008, State College, PA G. Comer Foundation Please note: I work for Pennsylvania State University, And help UN IPCC, NRC, etc., But I am not representing them, Just me. Ice Cores, Climate Change and Polar See-saws: What Nature Does And Doesn't Do To Our Climate Richard B. Alley Penn State

33. Ice core on light table, central Greenland. Depths of 1411.8 m and 1411.9 m (slightly less than a mile) are noted. The mass-loss summer layers have made bigger-bubbled layers that appear dark here (blue bars), and compaction and ice flow have moved the layers closer together. These are about 8400 years old.

34. + Ice cores give wonderful climate records • Age from counting annual layers, etc. (checked many ways!); • Snow accumulation from layer thickness with flow correction, other ways; • Temperature at site in several ways; • Wind-blown dust, sea-salt, etc. from elsewhere; • Trapped bubbles of old air with swamp-gas methane, etc.; • All on common time scale.

35. + Dating (ice-core age) • Count annual layers; • Count more than once (I re-did half a mile of Greenland ice); • In more than one way (visible, electrical, chemical, isotopic indicators); • By more than one person (blind intercomparisons--no cheating!); • Check vs. independent ages (chemically fingerprinted fallout of historically dated volcanoes; radiometric, tree-ring & varve ages of abrupt climate changes); • Other correlations (esp. all ice cores share same gas record), flow models, etc.

36. + Snow accumulation rate • Annual-layer thickness, after flow correction; • Ice sheet spreads and thins, melting at edges or making icebergs; • Snowfall more-or-less fills space from thinning; • Layers moving halfway to bed thinned by ~1/2; • Mathematically un-thin (also correct for air in bubbles) to get original thickness; • Others (change of snow to ice controlled by temperature and accumulation rate, and recorded in gas isotopes and bubble number density, so measure these and estimate past temperature to learn past accumulation).

37. + Others • If it blows through the air, it lands on the ice; • Dust, sea salt, pollen, micrometeorites, cosmic-ray-produced nuclides, volcanic ash, pollutant; • Once you know snow accumulation rate, you can tell whether an ice layer is “dirtier” because it received more dirt, or less snow to dilute dirt; • Thus, the ice yields histories of cosmic-ray intensity (modulated by sun and magnetic field), space-dust infall, dust production and transport, pollution, volcanic eruptions, etc; • Can fingerprint things--e.g., central Greenland dust from Asia, Antarctic dust from Patagonia.

38. + Temperature--Isotopic Ratios • ~1 molecule in 500 in ocean has 1 or 2 extra protons in one or more atoms: 2H (also called deuterium) instead of 1H, or 17O or 18O instead of 16O; • The heavier molecules evaporate with greater difficulty, condense more easily; • As air mass moves over ice sheet, heavy preferentially condenses to fall as snow; • Colder-->more water removed from air--> more heavy removed-->less heavy left--> isotopically ”lighter” snow.

39. + Temperature--Borehole Temperature • In Greenland, ice ~1 mile down colder than surface and colder than bed, because not done warming from ice age (works in Antarctica, and in ground, too); • Consider cooking a turkey vs. hot-dog vs. your skin if you touch the stove burner--twice as big takes four times as long; • Temperature of ice today “remembers” how cold the ice-age was; • Fuzzy memory--can learn temperature last night, last winter, last century, last millennium, and last ice age.

40. + Temperature--Gas isotopes • After abrupt warming, takes ~100 years to warm ice 70 m down where bubbles are trapped from the air spaces in the snow; • Takes ~5 years for gas to diffuse through spaces to bubble-trapping depth; • If not wind-mixed, heavy gases go to cold end (well-known physics; even tried for isolating uranium isotopes for bombs); • Causes slight anomaly in trapped gases; • Anomaly size shows abrupt-warming size.

41. + Temperature--More • Count years between ice-phase and gas-phase record of abrupt warming; • Measure gas-isotopic anomaly caused by gravitational separation to bubble-trapping depth in non-wind-mixed firn=old snow (Todd Sowers discovered); • Measure bubble number-density, controlled by time and temperature to trapping depth; • All three depend on snowfall and temperature over time to bury snow to trapping depth; • So allow check on temperature, snowfall history estimates.

42. + Gases • Snow turning to ice traps old air; • Only reliable samples of old air known; • Reliable? Yes. • Good agreement with instrumental record; • Good agreement between records from different cores from different places with different snowfall, temperature and impurities; • Records of abrupt changes offset by firn depth, not where chemistry changed; • “Breaking points” fairly well known (too warm or too dirty and get poor agreement among cores or with instrumental record, and gas changes where chemistry changes).

43. + So, ice cores show: • Sun matters to climate, but: • Total output changes little; • Redistribution by orbits slow; • Volcanoes matter to climate, but mostly noisemakers rather than organized; • Magnetic field, cosmic rays don’t matter to climate (at least not much); • Space dust doesn’t change much, so doesn’t matter to climate changes; • CO2 matters to climate; • Ocean circulation, sea ice matter to climate.

44. Year Temperature 1700 1800 1900 Sunspots We can see solar effect on climate--real but small (and sun hasn’t done anything while temperatures rose last decades). Greenland temperatures do correlate significantly with sunspot numbers, but most Greenland temperature changes are not explained by sunspots. (GISP2 ice-core 18O, 5-20 yr bandpass, data from 1700-1930, shifted for optimal correlation; correlation is highly significant, but accounts for only 13% of the power in the passband. Other solar frequencies are also present, but again with small power. Stuiver et al., 1995)

45. Volcano erupts Acid falls on Greenland Cooling from volcanoes Big volcanoes cool (1-2oC for 2-3 years). But, big volcanoes can’t get organized, so they haven’t & won’t control climate. (Stack of GISP2, Greenland 18O records from 7 VEI 6-7 eruptions; Stuiver et al. 1995.)

46. Today Climate didn’t change Warmer Climate didn’t change When more cosmic rays reached Earth Cosmic rays, magnetic field don’t matter much to climate. From Muschler et al., 2005, QSR. 18O (proxy for temperature) from GRIP core (top), the concentration of 10Be (middle), and the flux of 10Be (bottom). The Laschamp event of near-zero magnetic field (red arrow) allowed increased cosmic-ray flux producing more 10Be, but with no apparent effect on climate.

47. Changes in space dust have been small, and haven’t affected climate much. Helium-3 is mostly from space dust. If space dust changed a lot, that might affect climate some. But there has been little change in space dust over last 30,000 years (ice-core data shown here) and beyond (other data not shown). (Very rarely, a big meteorite does matter, such as the one that killed the dinosaurs 65 million years ago.) Winckler & Fischer, 2006, Science

50. Petit et al., 1999