1. G. Comer Foundation The Biggest Control Knob The more we learn of the large natural changes of the past, the more confident we are that humans are driving today Richard B. Alley, Penn State Please note: I work for Penn State University, And help UN IPCC, NRC, etc., But I am not representing them, Just me. Meteorology, 2011

2. Paleoclimatology What happened? Reconstruct past climate; When did it happen? Date past events; Why did it happen? Reconstruct possible causes of climate change, such as drifting continents, changes in the sun’s output, shifts in Earth’s orbit, eruptions of sun- blocking dust or fall of meteorite dust, changes in greenhouse gases, etc.

3. CO 2 Paleobarometers Gold standard is ice-core record; So far “only” 800,000 years, duplicated to 450,000 yrs, and multiply duplicated younger; How do we know it works?  Youngest samples agree with instrumental record  Antarctic sites with different temperature, snowfall and impurities give same record  Sensible “failures”; e.g., in rare refrozen- meltwater layers expect and find excess CO 2 localized, so diffusion isn’t smearing record. In warm tropical-glacier ice with dead bugs, find anomalously high CO 2 as expected.

4. CO 2 Paleobarometers Many others, based on influence of CO 2 abundance on something else that is preserved in sedimentary record, plus data- driven biogeochemical modeling; Nothing as simple and easy as ice-core data; Systematic errors of the different techniques are largely independent, so look for agreement among multiple techniques;

5. CO 2 Paleobarometers  13 C of alkenones, soil carbonates, or liverworts: faster diffusion of lighter species allows preferential use in plants if CO 2 abundant, but heavier used if CO 2 scarce;  11 B or B:Ca of foraminiferal shells: B(OH) 3 enriched in 11 B vs. the B(OH) 4 - incorporated in shells, and B residence time long, so  11 B or B:Ca paleo-pH meters linked to CO 2 Plant leaves grow more stomata when CO 2 lower; Offspring-of-BLAG modeling—track inputs and outputs of CO 2 from independent data (e.g., more volcanoes release more CO 2, and more fossil-fuel formation removes CO 2 from air)

6. History of Climate No instruments way back, so use proxies Find sediment-climate relations Past sand dunes, glaciers, or lakes easy to identify, tell different things about climate Some are mainly physics (Greenland’s ice is colder a mile down than ice above or below because still warming from ice age, tells how cold ice age was) Some based on assuming little change in modern correlations (e.g., relation between temperature and who lives where)—for such, we look for agreement among multiple independent indicators

7. History of Climate Find ages of sediments in many ways Oldest tree ~5000 years, but overlapping pattern of thick and thin rings in living and nearby dead wood to >12,000 years; we counted >100,000 years in Greenland ice (match historical volcanic fallout, etc. as far back as written history goes) Older, a host of damage-accumulation and radiometric-dating techniques Again, look for agreement among multiple ways

8. Big volcanoes cool (1-2 o C for 2-3 years). But, big volcanoes don’t get really organized (a little; Huybers & Langmuir, 2009), so explosive volcanoes don’t control climate. (Note that flood-basalt eruption does seem to warm.) (Stack of GISP2, Greenland  18 O records from 7 VEI 6-7 eruptions; Stuiver et al. 1995.) Volcano erupts Acid falls on Greenland Cooling from volcanoes

9. Figure 6.14. Simulated temperatures during the last 1 kyr with and without anthropogenic forcing, and also with weak or strong solar irradiance variations. Global mean radiative forcing (W m –2 ) used to drive climate model simulations due to (a) volcanic activity, (b) strong (blue) and weak (brown) solar irradiance variations, and (c) all other forcings, including greenhouse gases and tropospheric sulphate aerosols (the thin flat line after 1765 indicates the fixed anthropogenic forcing used in the ‘Nat’ simulations). (d) Annual mean NH temperature (°C) simulated by three climate models under the forcings shown in (a) to (c), compared with the concentration of overlapping NH temperature reconstructions (shown by grey shading, modified from Figure 6.10c to account for the 1500 to 1899 reference period used here). ‘All’ (thick lines) used anthropogenic and natural forcings; ‘Nat’ (thin lines) used only natural forcings. All forcings and temperatures are expressed as anomalies from their 1500 to 1899 means; the temperatures were then smoothed with a Gaussian-weighted filter to remove fluctuations on time scales less than 30 years. Note the different vertical scale used for the volcanic forcing compared with the other forcings. The individual series are identified in Table 6.3.

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

11. 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

12. Vostok, Petit et al.

16. CO 2 and temperature changed essentially together over ice- age cycles, as shown by Antarctic ice-core data.

17. But, the science shows that a bit of the warming happened over a few centuries before the CO 2 rose. The temperature never went far without the CO 2, but the CO 2 appears to have lagged temperature. What does that mean for CO 2 causing warming?

18. First, a modern analogy…

19. Overspending

20. Going into debt

21. Overspending Going into debt Interest payments

22. Overspending Going into debt Interest payments More debt

23. Overspending Going into debt Interest payments More debt Interest lags debt. How do we know interest adds to debt?

24. Overspending Going into debt Interest payments More debt Interest lags debt. How do we know interest adds to debt? We can’t explain size of debt without interest (and, economics says so)

25. Overspending Going into debt Interest payments More debt Interest lags debt. How do we know interest adds to debt? We can’t explain size of debt without interest (and, economics says so) Climate of the past

26. Overspending Going into debt Interest payments More debt Interest lags debt. How do we know interest adds to debt? We can’t explain size of debt without interest (and, economics says so) Orbits

27. Overspending Going into debt Interest payments More debt Interest lags debt. How do we know interest adds to debt? We can’t explain size of debt without interest (and, economics says so) Orbits Warming

28. Overspending Going into debt Interest payments More debt Interest lags debt. How do we know interest adds to debt? We can’t explain size of debt without interest (and, economics says so) Orbits Warming CO 2 rise

29. Overspending Going into debt Interest payments More debt Interest lags debt. How do we know interest adds to debt? We can’t explain size of debt without interest (and, economics says so) Orbits Warming CO 2 rise More warming

30. Overspending Going into debt Interest payments More debt Interest lags debt. How do we know interest adds to debt? We can’t explain size of debt without interest (and, economics says so) Orbits Warming CO 2 rise More warming CO 2 lags warming. How do we know CO 2 adds to warming?

31. Overspending Going into debt Interest payments More debt Interest lags debt. How do we know interest adds to debt? We can’t explain size of debt without interest (and, economics says so) Orbits Warming CO2 rise More warming CO 2 lags warming. How do we know CO 2 adds to warming? We can explain changes if and only if we include physics of CO 2 (places getting more sun cooled when CO 2 fell, and places getting less sun warmed as CO 2 rose) e.g., Jansen et al., 2007

32. CO 2 as part of ice-age cycling Ice ages paced by orbit Climate everywhere changed the same way, but orbits just moved sunshine around on the planet ~5-6 o C globally averaged surface temperature change despite almost zero change in total sun; Less summer sun in Canada  more ice  higher albedo (also more dust, changing vegetation, etc.); Set these to ice-age values in a climate model and get about half the cooling (but this is cheating, because need help from CO 2 to get these); Add greenhouse-gas changes and get the rest ( e.g., Jansen et al 2007 IPCC; Hansen et al 2008; Alley 2003; Cuffey & Brook 2000 )

33. Figure 4.24 Atmospheric CO2 and continental glaciation 400 Ma to present. Vertical blue bars, timing and palaeolatitudinal extent of ice sheets (after Crowley, 1998). Plotted CO2 records represent five-point running averages from each of four major proxies (see Royer, 2006 for details of compilation). Also plotted are the plausible ranges of CO2 derived from the geochemical carbon cycle model GEOCARB III (Berner and Kothavala, 2001). All data adjusted to the Gradstein et al. (2004) time scale. Continental ice sheets grow extensively when CO2 is low. (after Jansen, 2007, that report’s Figure 6.1)

34. CO 2 and climate over longer times Strong correlation of past CO 2 and temperature; Known physics of CO 2 explain most of this; Other things did contribute at some times (drifting continents, volcanic eruptions, etc.) But others physically inadequate to explain most large changes and not strongly correlated Warming increases CO 2 over “short” times but decreases CO 2 over long times (>≈500,000 years).

35. CO 2 (gas) CaSiO 3 (solid) Volcano— eruption rate independent of climate Rock Weathering— CaSiO 3 +3H 2 O+2CO 2  Ca +2 +H 4 SiO 4 +2HCO 3 - Faster when warmer Shell Growth— Ca +2 +H 4 SiO 4 +2HCO 3 -  CaCO 3 +SiO 2 +3H 2 O+CO 2 Shell subduction CaCO 3 +SiO 2 Walker, J.C.G., P.B. Hays and J.F. Kasting, 1981 Rock-Weathering Thermostat—Too cold, and CO 2 builds up to warm.

36. Many events show CO 2 -climate connection Faint young sun of 4 billion years ago; Snowball Earth’s of a billion or so years ago Ordovician glaciation End-Permian extinction “Saurian Sauna” of the Cretacteous Ocean Anoxic Events and black-shale formation Paleocene-Eocene Thermal Maximum Cooling since the Eocene Mid-Pliocene warmth I won’t subject you to all of them here, but we go over them in class

37. Climate sensitivity to CO 2 from paleo-history Overall, tests of climate models against paleo- record show that models are pretty good; Various suggested values range from <1 o C to ~12 o C; history excludes low and high values with fairly high confidence; ~3 o C warming for doubled CO 2 over decades, and somewhat larger over centuries to millennia, may not be too bad (see Hansen et al., 2008); No evidence that warming lowers sensitivity (ice- albedo isn’t that big for modern and warmer); Suggestion that there is something missing in models in warm climates in polar winters.

38. So, where does that leave us? If higher CO 2 warms, climate history sensible, as CO 2 caused or amplified the main changes; There is now no plausible alternative to this; If higher CO 2 does not warm, we must explain how radiation physicists are so wrong, and how a lot of really inexplicable climate events happened; CO 2 may be forcing or feedback—no matter how a CO 2 molecule got into air, it affects radiation; Paleoclimatic data show climate sensitivity similar to values in modern models (~3 o C for doubled CO 2 ), perhaps with somewhat higher values over long times especially in polar regions.

39. So, where does that leave us? Lots of knobs control the Earth’s climate system; The “Sun” knob isn’t twiddled very much over short times, and hasn’t done very much over long times because of CO 2 ; If cosmic-ray, space-dust, magnetic-field, other “space” knobs matter, available evidence indicates that they do no more than fine-tune, and even that is not demonstrated; Lots of things on Earth matter regionally—moving a continent from equator to pole cools it—but evidence weak for major control of global climate, except through CO 2