clim 690: scientific basis of climate change paleoclimate jim kinter18 feb 2010 ipcc working group...

CLIM 690: Scientific Basis of Climate Change Paleoclimate Jim Kinter18 Feb 2010 IPCC Working Group I: Chapter 6

CLIM 690: Scientific Basis of Climate Change WHAT IS CLIMATE?

CLIM 690: Scientific Basis of Climate Change WEATHER WHAT IS CLIMATE?

CLIM 690: Scientific Basis of Climate Change WEATHER CLIMATE WHAT IS CLIMATE?

CLIM 690: Scientific Basis of Climate Change Climate is a statistical representation of the slowly-varying conditions in the atmosphere, oceans and land surface during a given epoch of geologic time (the study of climate is a branch of the geosciences) WHAT IS CLIMATE?

CLIM 690: Scientific Basis of Climate Change Climate is a statistical representation of the slowly- varying conditions in the atmosphere, oceans and land surface during a given epoch of geologic time (the study of climate is a branch of the geosciences) WHAT IS CLIMATE? AGE OF DINOSAURS FORMATION OF FOSSIL FUELS (?)

CLIM 690: Scientific Basis of Climate Change Climate is a statistical representation of the slowly- varying conditions in the atmosphere, oceans and land surface during a given epoch of geologic time (the study of climate is a branch of the geosciences) WHAT IS CLIMATE? QUATERNARY - LAST ~2 MILLION YEARS: FOCUS OF RECENT CLIMATE

CLIM 690: Scientific Basis of Climate Change Questions for Paleoclimate Studies Obs & Methods How has climate varied before the historical record, and how do we know? What are the "proxies" of climate that can be observed by examining geologic and other records? How can we date these proxies? Is there evidence of climate change in the pre-monitoring past that is similar to what is being observed today in terms of magnitude and rapidity of fluctuation? Is there evidence of a direct link between greenhouse gas concentrations and other climate indicators (temperature, moisture, etc.)? Can a cause-effect relationship be inferred from the available evidence? E.g., is there a lead- lag relationship between CO 2 and glacial changes? How good are the paleoclimatic "proxies"? What temporal resolution? How representative of the globe? Seasons? Can we quantify the timing and/or magnitude of paleoclimatic changes?

CLIM 690: Scientific Basis of Climate Change A Word About Notation Ka(or ka)Thousands of years before present MaMillions of years before present GaBillions of years before present Examples: Current interglacial period began 14 ka Earth was formed 4.5 Ga

CLIM 690: Scientific Basis of Climate Change Evidence of Past Climates 1.Remote sensing from satellites (global; since 1979) 2.Instrumental surface record (mostly land points; since 1860) 3.Diaries, written records of flood, harvest, ice (spotty; 1 ka) 4.Proxy records (spotty) Tree Rings or dendrochronology (100 - 5 ka) Lake Cores, Packrat Middens (100 a - 10 ka) -- sediments, varves, pollen, seeds, C 14 (5730 a) Ice Cores (100 a - 600 ka) -- CO 2 bubbles, dust deposits, O 18 Loess Deposits (100 a - 100 ka) -- aeolian dust (windblown silt and clay), strata Ocean Cores (1 ka - 1 Ma) -- sediments, mud, isotopes Sedimentary Rocks (1 ka - 100 Ma) -- fossils, strata

CLIM 690: Scientific Basis of Climate Change C 14 dating proxy Radioactive C 14 (unstable isotope of carbon; C 12 is stable isotope) is produced in the atmosphere by cosmic ray bombardment. It has a half-life of 5730 years and constitutes about one percent of the carbon in an organism. When an organism dies, its C 14 continues to decay. The older the organism, the less C 14. O 18 temperature proxy Both O 18 and O 16 are stable isotopes of oxygen. Since O 18 has two more neutrons than O 16 water (H 2 O) containing O 18 is heavier, harder to evaporate (isotope fractionation). As temperature decreases (in an ice age), snow deposits contains less O 18 while ocean water and marine organisms (CaCO 3 ) contain more O 18. The O 18 / O 16 ratio or O 18 in ice and marine deposits constitutes a proxy thermometer that indicates ice ages and interglacials. Low O 18 in ice indicates it was deposited during cold conditions worldwide, while low O 18 in marine deposits indicates warmth.

CLIM 690: Scientific Basis of Climate Change Warm and Cold Periods in Earth History AGE OF DINOSAURS FORMATION OF FOSSIL FUELS QUATERNARY - LAST ~2 MILLION YEARS: ICE AGES, MODERN AGE

CLIMATE DYNAMICS OF THE PLANET EARTH S a g T4T4 WEATHERWEATHER CLIMATE. CLIMATE. hydrodynamic instabilities of shear flows; stratification & rotation; moist thermodynamics day-to-day weather fluctuations; wavelike motions: wavelength, period, amplitude S,, a, g, O 3 H 2 O CO 2 stationary waves (Q, h*), monsoons h*: mountains, oceans (SST) w*: forest, desert (soil wetness) (albedo)

CLIM 690: Scientific Basis of Climate Change Possible Origins of Climate Change

CLIM 690: Scientific Basis of Climate Change 5 Billion Years (Ga) (all of Earth history) Mechanisms: Galactic dust, Evolution of the Sun, Evolution of the Atmosphere

CLIM 690: Scientific Basis of Climate Change Earths Climate through Geologic Time Ma

CLIM 690: Scientific Basis of Climate Change Earths Climate through Geologic Time Carbon Cycle Faint Sun Paradox Ice-Covered Earth? Pre-Quaternary Eras o Pre-Cambrian (Proterozoic) o Paleozoic o Mesozoic o Cenozoic (Tertiary) Continental Drift Origin of Warmth During Cretaceous (Mesozoic) Asteroid Impact

CLIM 690: Scientific Basis of Climate Change Carbon Cycle Carbon is present in several forms on Earth. It is stored in several large reservoirs and is transported among the reservoirs by various processes. There are two principle modes of cycling carbon: organic and inorganic. Organic carbon cycle: 6 CO 2 + 6 H 2 O + h C 6 H 12 O 6 + 6 O 2 photosynthesis respiration C 6 H 12 O 6 + 3 CO 2 + 3 CH 4 anaerobic fermentation NET: 3 CO 2 + 6 H 2 O 3 CH 4 Inorganic carbon cycle: CO 2 + H 2 O H 2 CO 3 formation of carbonic acid H 2 CO 3 H + + HCO 3 - bicarbonate ion HCO 3 - H + + CO 3 -- carbonate ion CaCO 3 + H 2 CO 3 Ca ++ + 2HCO 3 - Calcium carbonate (calcite) weathering CaSiO 3 + 2H 2 CO 3 Ca ++ + 2HCO 3 - + SiO 2 + H 2 O silicate weathering (consumes 2X carbon) Ca ++ + 2HCO 3 CaCO 3 + H 2 CO 3 carbonate precipitation in shells NET: CaSiO 3 + CO 2 CaCO 3 + SiO 2

CLIM 690: Scientific Basis of Climate Change Carbon Cycle Organic carbon cycling: Net results molecular oxygen (O 2 ) and methane (CH 4 ). The transitions from one side to the other of these equilibria are primarily associated with plant respiration and decay of plant matter by microbial consumption, and are relatively fast, on geologic time scales. Inorganic carbon cycling: Net result - equilibrium between wollastonite (CaSiO 3 ) plus CO 2 and calcium carbonate plus silicate (sand or quartz; SiO 2 ). CaSiO 3 + CO 2 CaCO 3 + SiO 2 The three minerals exist in equilibrium with CO 2. Weathering at the Earths surface drives the equilibrium to the right favoring calcium carbonate and silicate. Metamorphosis, usually by subduction of tectonic plates, drives the equilibrium to the left, favoring wollastonite and CO 2. This process occurs slowly on geologic time scales.

CLIM 690: Scientific Basis of Climate Change Faint Sun Paradox (Archaen Period) The solar constant is 30% larger today than it was 4.5 Ga due to evolution of Sun (thermonuclear transformation from H to He makes core denser and hotter). BUT We have no evidence of glaciation before ~2.3 Ga (running water on Earth, Mars surfaces for billions of years) THEREFORE Feedbacks are required! Candidates include: Bolide impacts heating More volcanism outgassing of CO 2 Smaller continents Reduced weathering more CO 2 Lower albedo (less surface for land ice) Less biota more CO 2

CLIM 690: Scientific Basis of Climate Change Ice-Covered Earth? (Proterozoic Period) There is evidence of a snow- or ice-covered tropics at ~700 Ma possibly due to very low values of CO 2 associated with rapid, unchecked weathering in tropics. If the Earth was ice-covered at some time, how did it become ice-free? Possibility: Some geologic evidence suggests that the tropics were glaciated about 0.5-1.0 Ma Hypothesis (Kirshvink, 1992): Plate tectonics increases CO 2 in the atmosphere through metamorphosis of calcium carbonate and silicate subduction (see carbon cycle discussion). In the absence of weathering and/or photosynthesis to remove CO 2 from the atmosphere, CO 2 builds up to sufficiently high levels to melt the ice. Evidence: Thick layers of carbonate are found on top of evidence of tropical glaciation Evidence: banded iron formations are found at the time of the tropical glaciation which could be due to an abundance of sea ice tropical oceans anoxic large iron solutions in oceans that sediment out as iron oxide (rust) when oceans become ice-free Implication: The era of iceball Earth lasted ~10 7 years and was followed by rapid transition to very warm climate large forcing changes on life forms over evolutionary time scales

CLIM 690: Scientific Basis of Climate Change Other Pre-Quaternary Eras Pre-Cambrian (Proterozoic): 2.7-0.6 Ga Evidence of first glaciation at ~2.5 Ga Issue: No evidence of glaciation between 2.5 and 0.9 Ga, even though Sun was faint Evidence of three major glaciations at 950, 750 and 610 Ma with ice occurring at low latitudes (paleomagnetic evidence) Paleozoic: 570 225 Ma Generally mild climate with two phases of ice Mesozoic: 225 65 Ma Period of the dinosaurs Generally non-glacial climate due to land-sea distribution and (possibly) high CO 2 Cenozoic (Tertiary): 65 3 Ma Sequential cooling and drying due to: Uplift of Tibetan Plateau and Rockies/Andes cordillera Changes in CO 2 - Paleocene-Eocene Thermal Max Changes in ocean heat transport

CLIM 690: Scientific Basis of Climate Change Paleocene-Eocene Thermal Max Records in benthic (bottom dwelling) foraminifer (Nuttallides truempyi) isotopic records from sites in the Antarctic, south Atlantic and Pacific show: Rapid decrease in carbon isotope ratios * Top: large increase in GHG (CO 2 and CH 4 ) * Middle: 5C global warming CH 4 released by rapid decomposition of marine hydrates might have been a major component (~2,000 GtC) of the carbon flux. Much of the additional greenhouse carbon would have been absorbed by the ocean, thereby lowering seawater pH and causing widespread dissolution of seafloor carbonates (bottom panel). Oceans carbonate saturation horizon rapidly shoaled more than 2 km, and then gradually recovered as buffering processes slowly restored the chemical balance of the ocean. (AR4 - Fig. 6.2) Benthic foraminifera

CLIM 690: Scientific Basis of Climate Change Continental Drift

CLIM 690: Scientific Basis of Climate Change Continental Drift As continents drift toward the poles, land serves as a platform for ice formation cooler climate Continents can drift apart to open ocean currents, e.g., the Southern Ocean opened when Antarctica separated from South America reduced oceanic heat transport cooler climate Continents can drift together closing off ocean currents, e.g., the isthmus of Panama formed when North and South America came together, cutting off the flow from west to east strengthening Gulf Stream increased oceanic heat transport warmer climate Uplift of Tibetan Plateau Indian monsoon Increased rainfall in south Asia, southeast Asia Increased subsidence & less rainfall over Mediterranean Warm rain perturbs carbon cycle (more weathering), so that, on time scales of 10 6 years, atmospheric CO 2 concentration is determined by balance of weathering and metamorphosis (subduction) Increased sea floor spreading increased volcanism increased CO 2 increased sea area, decreased land area decreased weathering increased CO 2 BREAK FOR CLIMAP SLIDESHOW

CLIM 690: Scientific Basis of Climate Change Origin of Warmth During Cretaceous (65-130 Ma) Climate models used with various boundary conditions (SST, geography etc.) assumed to be prevalent during Cretaceous cannot explain high latitude warmth THEREFORE Need higher CO 2 (as much as 4X to 8X current level) Higher rate of volcanism 20% less land area Higher CO 2 implies three feedbacks: Higher water vapor concentration increased latent heat transport to high latitudes Decreased meridional temperature gradient decreased sensible heat transport to high latitudes Thermal expansion of sea water increased oceanic heat transport to high latitudes

CLIM 690: Scientific Basis of Climate Change PRE-QUATERNARY CLIMATE (Top) Global compilation of deep-sea benthic foraminifera 18 O isotope records from 40 Deep Sea Drilling Program and Ocean Drilling Program sites. After the early Oligocene much of the variability (~70%) in the 18 O record reflects changes in Antarctic and Northern Hemisphere ice volume, which is represented by light blue horizontal bars. Where the bars are dashed, they represent periods of ephemeral ice or ice sheets smaller than present, while the solid bars represent ice sheets of modern or greater size. (Bottom) Detailed record of CO 2 for the last 65 Myr. Individual records of CO 2 and associated errors are color-coded by proxy method; when possible, records are based on replicate samples. Dating errors are typically less than 1 Myr. Also plotted are the plausible ranges of CO 2 from three geochemical carbon cycle models. (AR4 - Fig. 6.1)

CLIM 690: Scientific Basis of Climate Change Asteroid Impact When a large rocky object (bollide) collides with the Earth, very large perturbations are introduced. On climate scales, there are short-term and long- term consequences. Initially, the kinetic energy of the bollide is transferred to the atmosphere sufficient to warm the global mean temperature near the surface by 30 K over the first 30 days after the impact. The ejecta that are thrown up by the impact return to Earth over several days to weeks produce radiative heating of the atmosphere sufficient to ignite global wildfires that kill most large vertebrates. Over several weeks to months, a global cloud of dust obscures the Sun, cooling the Earths surface, effectively eliminating photosynthesis and stabilizing the atmosphere to the degree that the hydrologic cycle is cut off. The sum of these effects together could kill most flora. The latter results in extinction up the food chain and a large increase in atmospheric CO 2, enabling a large warming of the climate in the period after the dust cloud has settled back to Earth. This is hypothesized to have happened at the Cretaceous-Tertiary boundary (65 Ma) that coincided with a very large mass extinction of a multitude of species, including the dinosaurs.

CLIM 690: Scientific Basis of Climate Change 180 Ma Mechanisms: Evolution of the Atmosphere, Plate Tectonics, Mountain Building, Volcanic Activity, Solar Variability, Ocean Circulation

CLIM 690: Scientific Basis of Climate Change 1 Ma Mechanism: Orbital Parameters

CLIM 690: Scientific Basis of Climate Change 120 ka Mechanism: Orbital Parameters

CLIM 690: Scientific Basis of Climate Change 18 ka

CLIM 690: Scientific Basis of Climate Change James Croll (1821-1890) Leading proponent of an astronomical theory of climate change in the 19 th century. Checkered career including caretaker at Andersonian College and Museum in Glasgow and secretary and accountant for the Scottish Geological Survey. Theory of ice ages took into account variations in orbital eccentricity, precession of the equinoxes, and obliquity of the ecliptic. Pioneer in Climate Dynamics. Feedback mechanisms -- radiative effects of the ice fields, enhanced formation of cloud and fog, changes in sea level, and the mixing and redirection of warm and cold ocean currents enhance the climatic changes initiated by the orbital elements.

CLIM 690: Scientific Basis of Climate Change Milutin Milankovitch (1879-1958) Leading proponent of an astronomical theory of climate change in the 20 th century. Worked in Serbia under extreme duress including incarceration in 1914 by the Austro-Hungarian Army and the bombing of Belgrade (and his publisher!) in 1941. Calculated mathematically the timing and influence at different latitudes of changes in orbital eccentricity, precession of the equinoxes, and obliquity of the ecliptic. This theory was confirmed in 1976 in the paleoclimatic proxy record, so Milankovitch cycles became known as the pacemaker of the ice ages.

CLIM 690: Scientific Basis of Climate Change Energy Received From Sun Varies On Geologic Time Scales Earth orbit variability

CLIM 690: Scientific Basis of Climate Change Orbital eccentricity (96,000 years) Large e --> 20% energy difference between S and W Large e also changes the length of the seasons Small e --> 7% energy difference between S and W Highly EllipticalAlmost Circular

CLIM 690: Scientific Basis of Climate Change Polar tilt or Obliquity of the ecliptic (42,000 years) 21.5 to 24.5 is the range -- currently 23.5 Small tilt = less seasonal variation cooler summers (less snow melt), warmer winters (more snowfall)

CLIM 690: Scientific Basis of Climate Change Polar wobble or Precession of equinoxes (24,000 years) Vernal equinox has 24 Ka period around the orbit. Wandering pole star. Caused by Moons gravitational pull on Earths equatorial bulge.

CLIM 690: Scientific Basis of Climate Change Polar Wobble (Precession of the Equinoxes) and Polar Tilt 12,000 years 21 June 21 December

CLIM 690: Scientific Basis of Climate Change Eccentricity (96 Kyrs) Obliquity (42 Kyrs) Precession (24 Kyrs) Total Insolation (solar radiation) Solar Radiation Received and Earth Orbital Parameters

CLIM 690: Scientific Basis of Climate Change Box 6.1, Figure 1 (Left) December to February (top), annual mean (middle) and June to August (bottom) latitudinal distribution of present-day (year 1950) incoming mean solar radiation (W m 2 ). (Right) Deviations with respect to the present of December to February (top), annual mean (middle) and June to August (bottom) latitudinal distribution of incoming mean solar radiation (W m 2 ) from the past 500 ka to the future 100 ka. (AR4 - Box 6.1, Fig. 1) DJF JJA Annual mean Present day

CLIM 690: Scientific Basis of Climate Change Power Spectrum shows Milankovitch cycles http://geography.otago.ac.nz/OnlineCo urses/Climate_Change_The_Past/Res ources/milankovitch.html

CLIM 690: Scientific Basis of Climate Change Ice Age Milankovitch cycle gives minimum insolation Glaciers advance Lower sea levels Lower sea surface temperatures Reduced evaporation and precipitation Polar front moves south Salinity increases Thermohaline circulation increases Nutrients and biological productivity increase Deep water sequesters CO 2 from atmosphere Cooling due to expanding ice caps and decreased CO 2

CLIM 690: Scientific Basis of Climate Change Last Glacial Maximum: 22-14 ka NH: Laurentide and Fennoscandian ice sheets 3.5 4 km thick 50-60 x 10 6 km 3 water 120 m sea level reduction 700 800 m crustal depression (currently in post-glacial isostatic adjustment of about 1 cm/year) Large changes in flora and fauna Most of planet equatorward of ice sheets: colder and drier wind speed 20 50% higher higher dust levels lower CO 2 concentration (~200 ppm) and CH 4 concentration feedback

CLIM 690: Scientific Basis of Climate Change Ice Age World: 18 ka

CLIM 690: Scientific Basis of Climate Change Figure 6.7 DANSGAARD-OESCHGER AND HEINRICH EVENTS The evolution of climate indicators from the NH (panels a to d), and from Antarctica (panels e to g), over the period 64 to 30 ka. (a) Anhysteretic remanent magnetisation (ARM), a proxy of the northward extent of Atlantic MOC, from an ocean sediment core from the Nordic Seas. (b) CH 4 as recorded in Greenland ice cores at the Greenland Ice Core Project (GRIP), Greenland Ice Sheet Project (GISP) and North GRIP (NGRIP) sites. (c) Surface temperature estimated from nitrogen isotope ratios that are influenced by thermal diffusion. (d) d 18 O, a proxy for surface temperature, from NGRIP (2004) with the D-O NH warm events 8, 12, 14 and 17 indicated. (e) 18 O from Byrd, Antarctica with A1 to A4 denoting Antarctic warm events. (f) NSS-Ca 2+, a proxy of dust and iron deposition, from Dome C, Antarctica; and (g) CO 2 as recorded in ice from Taylor Dome, Antarctica. The Heinrich events (periods of massive ice-rafted debris recorded in marine sediments) H3, H4, H5, H5.2, and H6, are shown. CH 4 variations are synchronous within the resolution of 50 years with variations in Greenland temperature, but a detailed analysis suggests that CH 4 rises lag temperature increases at the onset of the D-O events by 25 to 70 years. The evolution of Greenland and Antarctic temperature is consistent with a reorganization of the heat transport and the MOC in the Atlantic. (AR4 - Fig. 6.7)

CLIM 690: Scientific Basis of Climate Change Milankovitch cycle gives maximum insolation Glaciers retreat Higher sea levels Higher sea surface temperatures Enhanced evaporation and precipitation Polar front moves north Salinity decreases Thermohaline circulation decreases Nutrients and biological productivity decrease Deep water releases CO 2 to atmosphere Warming due to shrinking ice caps and increased CO 2 Abrupt warming: one of most rapid transitions Interrupted by brief period of cold Younger Dryas (~11 ka) Continuation of warming beginning in ~10 ka Interglacial (Holocene)

CLIM 690: Scientific Basis of Climate Change Figure 6.8 SEA LEVEL CHANGE (A) The ice-equivalent eustatic sea level history over the last glacial-interglacial cycle. The smooth black line defines the mid-point of their estimates for each age and the surrounding hatched region provides an estimate of error. The red line is the prediction of the ICE-5G(VM2) model for the Barbados location. (B) The fit of the ICE-5G(VM2) model prediction (red line) to the extended coral- based record of RSL history from the island of Barbados in the Caribbean Sea over the age range from 32 ka to present. The actual ice- equivalent eustatic sea level curve for this model is shown as the step-discontinuous purple line. The individual coral-based estimates of RSL (blue) have an attached error bar that depends upon the coral species. The data denoted by the coloured crosses are from the ice-equivalent eustatic sea level reconstruction for Barbados (cyan), Tahiti (grey), Huon (black), Bonaparte Gulf (orange) and Sunda Shelf (purple). (AR4 - Fig. 6.8)

CLIM 690: Scientific Basis of Climate Change Climate Reconstructions: Last 1800 years [Jones and Mann, 2004, Reviews of Geophysics]. Model-based estimates of northern hemisphere temperature variations over the past two millennia. Shown are 40 year smoothed series. The simulations are based on varying radiative forcing histories employing a hierarchy of models including one-dimensional energy based models (Crowley, 2000), two-dimensional reduced complexity models (Bauer et al, 2003; Bertrand et al, 2002; Gerber et al, 2003), and full three-dimensional coupled atmosphere-ocean general circulation (GKSS-Gonzalez-Rouco et al, 2003; CSMAmmann et al., submitted). Shown for comparison is the instrumental northern hemisphere record 1856-2003 (Jones et al, 1999), and the proxy-based estimate of Mann and Jones (2003) extended through 1995, with its 95% confidence interval. Models have been aligned vertically to have the same mean over the common 1856- 1980 period as the instrumental series (which is assigned zero mean during the 1961-1990 reference period).

CLIM 690: Scientific Basis of Climate Change

Figure 6.9 Timing and intensity of maximum temperature deviation from pre-industrial levels, as a function of latitude (vertical axis) and time (horizontal axis, in thousands of years before present ). Temperatures above pre-industrial levels by 0.5C to 2C appear in orange (above 2C in red). Temperatures below pre-industrial levels by 0.5C to 2C appear in blue. (AR4 - Fig. 6.9)

CLIM 690: Scientific Basis of Climate Change Box 6.3, Figure 1 GLACIER RETREAT Timing and relative scale of selected glacier records from both hemispheres. The different records show that Holocene glacier patterns are complex and that they should be interpreted regionally in terms of precipitation and temperature. In most cases, the scale of glacier retreat is unknown and indicated on a relative scale. Lines above the horizontal line indicate glaciers smaller than at the end of the 20th century and lines below the horizontal line denote periods with larger glaciers than at the end of the 20th century. The radiocarbon dates are calibrated and all curves are presented in calendar years. (AR4 - Box 6.3, Fig. 1)

CLIM 690: Scientific Basis of Climate Change Figure 6.11 Locations of proxy records with data back to AD 1000, 1500 and 1750 (instrumental: red thermometers; tree ring: brown triangles; borehole: black circles; ice core/ice borehole: blue stars; other including low-resolution records: purple squares) that have been used to reconstruct NH or SH temperatures by studies shown in Figure 6.10 or used to indicate SH regional temperatures (Figure 6.12). (AR4 - Fig. 6.11)

CLIM 690: Scientific Basis of Climate Change Figure 6.10 THE LAST MILLENIUM - NH Records of NH temperature variation during the last 1.3 kyr. (a) Annual mean instrumental temperature records. (b) Reconstructions using multiple climate proxy records. (c) Overlap of the published multi-decadal time scale uncertainty ranges of all temperature reconstructions, with temperatures within 1 standard error (SE) of a reconstruction scoring 10%, and regions within the 5 to 95% range scoring 5% (the maximum 100% is obtained only for temperatures that fall within 1 SE of all 10 reconstructions). The HadCRUT2v instrumental temperature record is shown in black. All series have been smoothed with a Gaussian-weighted filter to remove fluctuations on time scales less than 30 years; smoothed values are obtained up to both ends of each record by extending the records with the mean of the adjacent existing values. All temperatures represent anomalies (C) from the 1961 to 1990 mean. (AR4 - Fig. 6.10)

CLIM 690: Scientific Basis of Climate Change Figure 6.12 THE LAST MILLENIUM - SH Temperature reconstructions for regions in the SH: two annual temperature series from South American tree ring data; annual temperature estimates from borehole inversions for southern Africa and Australia; summer temperature series from Tasmania and New Zealand tree ring data. The black curves show summer or annual instrumental temperatures for each region. All tree ring and instrumental series were smoothed with a 25-year filter and represent anomalies (C) from the 1961 to 1990 mean (indicated by the horizontal lines). (AR4 - Fig. 6.12)

CLIM 690: Scientific Basis of Climate Change Figure 6.13 THE LAST MILLENIUM - MODELS Radiative forcings and simulated temperatures during the last 1.1 ka. Global mean radiative forcing (W m 2 ) used to drive climate model simulations due to (a) volcanic activity, (b) solar irradiance variations and (c) all other forcings (which vary between models, but always include greenhouse gases, and, except for those with dotted lines after 1900, tropospheric sulphate aerosols). (d) Annual mean NH temperature (C) simulated under the range of 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 forcings and temperatures are expressed as anomalies from their 1500 to 1899 means and then smoothed with a Gaussian-weighted filter to remove fluctuations on time scales less than 30 years; smoothed values are obtained up to both ends of each record by extending the records with the mean of the adjacent existing values. (AR4 - Fig. 6.13)

CLIM 690: Scientific Basis of Climate Change Figure 6.14 NATURAL VS. ANTHROPOGENIC Simulated temperatures during the last 1 ka 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). 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. (AR4 - Fig. 6.14)

CLIM 690: Scientific Basis of Climate Change Questions for Paleoclimate Studies - Mechanisms What processes can we infer are responsible for paleoclimatic variability? Why do ice sheets grow initially? What is the origin of the abrupt events in the Quaternary, e.g., warming at 13 ka, Dansgaard-Oeschger events, Heinrich events? What is the origin of the 100 ka periodicity in ice ages? If the 100 ka periodicity is explainable with ice volume mechanisms, what is the origin of similar periodicity observed prior to 2 Ma? What is the origin of decadal-millenial variability solar fluctuations, volcanoes, ocean circulation, or something else?

CLIM 690: Scientific Basis of Climate Change Raises many scientific questions: Which is cause and which is effect? Or is it a coupled system? What determines the time scale? Is Antartica representative of the global situation?

CLIM 690: Scientific Basis of Climate Change IPCC Working Group I Chapter 6 Paleoclimate

CLIM 690: Scientific Basis of Climate Change IPCC AR4 WG1 - Paleoclimate Major conclusions - GHG Sustained rate of increase over past 100 yrs in combined radiative forcing of CO 2, CH 4 and N 2 O is very likely unprecedented in at least 16 ka It is very likely that current CO 2 and CH 4 concentrations far exceed natural range of past 650 ka It is very likely that glacial-interglacial CO 2 variations have strongly amplified climate variations but unlikely that CO 2 variations triggered the end of glacial periods It is likely that earlier periods with higher than present CO 2 concentration were warmer than present (e.g. Pliocene ~3-5 Ma and Paleocene-Eocene Thermal Max at 55 Ma) with warming likely strongly amplified at high latitudes

CLIM 690: Scientific Basis of Climate Change IPCC AR4 WG1 - Paleoclimate Major conclusions - glacial-interglacial variability Climate models: LGM (21 ka) was 3-5C cooler globally than present due to changes in GHG forcing and ice sheet conditions; atmospheric dust and vegetation changes accounts for additional 1-2C cooling (not well understood) Warming since LGM about 10X slower than warming in C20 Ocean proxy records of LGM: tropical SST 2-3C cooler and expanded high-lat sea ice Land proxy records of LGM: significant cooling in tropics (5C) and greater magnitude in high latitudes Virtually certain that global temperatures in coming centuries will not be influenced by orbital variations; no new ice age for at least 30 ka Global sea level likely 4-6 m higher during last interglacial (125 ka) than in C20

CLIM 690: Scientific Basis of Climate Change IPCC AR4 WG1 - Paleoclimate Major conclusions - current interglacial period Unlikely that any regional, transient warm periods over last 10 ka were globally synchronous Glaciers in NH mtns retreated between 11 and 5 ka due to orbital forcing (may have been smaller at 5 ka than C20) Current near-global retreat of mountain glaciers cannot be attributed to same natural causes, because orbital forcing trend of past 5 ka has been toward cooler summer in NH Climate models: simulations of mid-Holocene (6 ka) represent many robust qualitative large-scale features in paleorecords Climate models: northward boreal treeline shifts likely result in significant feedback Abrupt shifts in regional frequency of tropical cyclones, floods, decadal droughts and the intensity of the Asian summer monsoon very likely occurred in past 10 ka (poorly understood)

CLIM 690: Scientific Basis of Climate Change IPCC AR4 WG1 - Paleoclimate Major conclusions - past 2 ka vs. C20 Very likely that average rates of increase of CO 2 at least 5X faster in 1960-1999 than over any other 40years in 2 ka Greenland ice core data: very likely rapid post-industrial era increase in sulphate concentrations Very likely that average NH temperature during second of C20 higher than for any other 50-year period in past 500 yrs Likely that 1950-2000 was warmest 50-year period in past 1.3 ka and warmth more widespread Climate models: increase in temperature since 1950 very unlikely reproducible without including anthropogenic GHG; very unlikely that warming is continuation of recovery from pre-C20 cold period SH paleoclimate very poorly measured Decadal droughts in Africa and the Americas were recurrent feature of past 2 ka.

CLIM 690: Scientific Basis of Climate Change IPCC AR4 WG1 - Paleoclimate Major conclusions - feedback and BGC cycles Amplification of orbitally-forced glacial-interglacial cycles very likely influenced by changes in GHG and ice sheet growth/decay, but also by ocean circulation and sea ice changes, biophysical feedbacks and aerosols Very likely that marine carbon cycle processes primarily responsible for glacial-interglacial CO 2 variations (mechanisms poorly understood) Regional vegetation composition and structure very likely sensitive to climate change; can respond within decades

CLIM 690: Scientific Basis of Climate Change

Figure 6.1 PRE-QUATERNARY CLIMATE (Top) Atmospheric CO 2 and continental glaciation 400 Ma to present. Vertical blue bars mark the timing and palaeolatitudinal extent of ice sheets. Plotted CO 2 records represent five-point running averages from each of the four major proxies. Also plotted are the plausible ranges of CO 2 from the geochemical carbon cycle model GEOCARB III. (Middle) Global compilation of deep-sea benthic foraminifera 18 O isotope records from 40 Deep Sea Drilling Program and Ocean Drilling Program sites. After the early Oligocene much of the variability (~70%) in the 18 O record reflects changes in Antarctic and Northern Hemisphere ice volume, which is represented by light blue horizontal bars. Where the bars are dashed, they represent periods of ephemeral ice or ice sheets smaller than present, while the solid bars represent ice sheets of modern or greater size. (Bottom) Detailed record of CO 2 for the last 65 Myr. Individual records of CO 2 and associated errors are color-coded by proxy method; when possible, records are based on replicate samples. Dating errors are typically less than 1 Myr. Also plotted are the plausible ranges of CO 2 from three geochemical carbon cycle models. (AR4 - Fig. 6.1)

CLIM 690: Scientific Basis of Climate Change Figure 6.2 PRE-QUATERNARY CLIMATE The Paleocene-Eocene Thermal Maximum as recorded in benthic (bottom dwelling) foraminifer (Nuttallides truempyi) isotopic records from sites in the Antarctic, south Atlantic and Pacific. The rapid decrease in carbon isotope ratios in the top panel is indicative of a large increase in atmospheric greenhouse gases CO 2 and CH 4 that was coincident with an approximately 5C global warming (centre panel). Using the carbon isotope records, numerical models show that CH 4 released by the rapid decomposition of marine hydrates might have been a major component (~2,000 GtC) of the carbon flux. In theory, much of the additional greenhouse carbon would have been absorbed by the ocean, thereby lowering seawater pH and causing widespread dissolution of seafloor carbonates. Such a response is evident in the lower panel, which shows a transient reduction in the carbonate (CaCO 3 ) content of sediments in two cores from the south Atlantic. The observed patterns indicate that the oceans carbonate saturation horizon rapidly shoaled more than 2 km, and then gradually recovered as buffering processes slowly restored the chemical balance of the ocean. (AR4 - Fig. 6.2)

CLIM 690: Scientific Basis of Climate Change Figure 6.3 CLIMATE OF THE PAST 650 ka Variations of deuterium (black), a proxy for local temperature, and the atmospheric concentrations of the greenhouse gases CO 2 (red), CH 4 (blue), and nitrous oxide (N 2 O; green) derived from air trapped within ice cores from Antarctica and from recent atmospheric measurements. The shading indicates interglacial warm periods. The length of the current interglacial is not unusual in the context of the last 650 kyr. The globally distributed benthic 18 O marine records (dark grey), a proxy for global ice volume fluctuations, is displayed for comparison with the ice core data. Downward trends in the benthic 18 O curve reflect increasing ice volumes on land. (AR4 - Fig. 6.3) Fig. 6.7

CLIM 690: Scientific Basis of Climate Change Figure 6.4

CLIM 690: Scientific Basis of Climate Change Figure 6.5 LAST GLACIAL MAXIMUM climate (approximately 21 ka) relative to the pre-industrial (1750) climate. (Top left) Global annual mean radiative influences (W m 2 ) of LGM climate change agents. A judgment of each estimates reliability is given as a level of scientific understanding based on uncertainties in the climate change agents and physical understanding of their radiative effects. (Bottom left) Multi-model average SST change for LGM PMIP-2 simulations by five AOGCMs. Ice extent over continents is shown in white. (Right) LGM regional cooling compared to LGM global cooling as simulated in PMIP-2, with AOGCM results shown as red circles and EMIC (ECBilt-CLIO) results shown as blue circles. Grey shading indicates the range of observed proxy estimates of regional cooling. (AR4 - Fig. 6.5)

CLIM 690: Scientific Basis of Climate Change Figure 6.6 LAST INTER-GLACIAL CLIMATE. Summer surface air temperature change over the Arctic (left) and annual minimum ice thickness and extent for Greenland and western arctic glaciers (right) for the LIG from a multi-model and a multi-proxy synthesis. The multi- model summer warming simulated by the CCSM, 130 ka minus present, and ECHO-G, 125 ka minus pre-industrial, is contoured in the left panel and is overlain by proxy estimates of maximum summer warming from terrestrial (circles) and marine (diamonds) sites. Extents and thicknesses of the Greenland Ice Sheet and eastern Canadian and Iceland glaciers are shown at their minimum extent for the LIG as a multi-model average from three ice models. Ice core observations indicate LIG ice (white dots) at Renland (R), North Greenland Ice Core Project (N), Summit (S, Greenland Ice Core Project and Greenland Ice Sheet Project 2) and possibly Camp Century (C), but no LIG ice (black dots) at Devon (De) and Agassiz (A) in the eastern Canadian Arctic. (AR4 - Fig. 6.6)

CLIM 690: Scientific Basis of Climate Change Figure 6.7 DANSGAARD-OESCHGER AND HEINRICH EVENTS The evolution of climate indicators from the NH (panels a to d), and from Antarctica (panels e to g), over the period 64 to 30 ka. (a) Anhysteretic remanent magnetisation (ARM), a proxy of the northward extent of Atlantic MOC, from an ocean sediment core from the Nordic Seas. (b) CH 4 as recorded in Greenland ice cores at the Greenland Ice Core Project (GRIP), Greenland Ice Sheet Project (GISP) and North GRIP (NGRIP) sites. (c) Surface temperature estimated from nitrogen isotope ratios that are influenced by thermal diffusion. (d) d 18 O, a proxy for surface temperature, from NGRIP (2004) with the D-O NH warm events 8, 12, 14 and 17 indicated. (e) 18 O from Byrd, Antarctica with A1 to A4 denoting Antarctic warm events. (f) NSS-Ca 2+, a proxy of dust and iron deposition, from Dome C, Antarctica; and (g) CO 2 as recorded in ice from Taylor Dome, Antarctica. The Heinrich events (periods of massive ice-rafted debris recorded in marine sediments) H3, H4, H5, H5.2, and H6, are shown. CH 4 variations are synchronous within the resolution of 50 years with variations in Greenland temperature, but a detailed analysis suggests that CH 4 rises lag temperature increases at the onset of the D-O events by 25 to 70 years. The evolution of Greenland and Antarctic temperature is consistent with a reorganization of the heat transport and the MOC in the Atlantic. (AR4 - Fig. 6.7)

CLIM 690: Scientific Basis of Climate Change Figure 6.8 SEA LEVEL CHANGE (A) The ice-equivalent eustatic sea level history over the last glacial-interglacial cycle. The smooth black line defines the mid-point of their estimates for each age and the surrounding hatched region provides an estimate of error. The red line is the prediction of the ICE-5G(VM2) model for the Barbados location. (B) The fit of the ICE-5G(VM2) model prediction (red line) to the extended coral- based record of RSL history from the island of Barbados in the Caribbean Sea over the age range from 32 ka to present. The actual ice- equivalent eustatic sea level curve for this model is shown as the step-discontinuous purple line. The individual coral-based estimates of RSL (blue) have an attached error bar that depends upon the coral species. The data denoted by the coloured crosses are from the ice-equivalent eustatic sea level reconstruction for Barbados (cyan), Tahiti (grey), Huon (black), Bonaparte Gulf (orange) and Sunda Shelf (purple). (AR4 - Fig. 6.8)

CLIM 690: Scientific Basis of Climate Change Figure 6.9 Timing and intensity of maximum temperature deviation from pre-industrial levels, as a function of latitude (vertical axis) and time (horizontal axis, in thousands of years before present ). Temperatures above pre-industrial levels by 0.5C to 2C appear in orange (above 2C in red). Temperatures below pre-industrial levels by 0.5C to 2C appear in blue. (AR4 - Fig. 6.9)

CLIM 690: Scientific Basis of Climate Change Figure 6.11 Locations of proxy records with data back to AD 1000, 1500 and 1750 (instrumental: red thermometers; tree ring: brown triangles; borehole: black circles; ice core/ice borehole: blue stars; other including low-resolution records: purple squares) that have been used to reconstruct NH or SH temperatures by studies shown in Figure 6.10 or used to indicate SH regional temperatures (Figure 6.12). (AR4 - Fig. 6.11)

CLIM 690: Scientific Basis of Climate Change Figure 6.10 THE LAST MILLENIUM - NH Records of NH temperature variation during the last 1.3 kyr. (a) Annual mean instrumental temperature records. (b) Reconstructions using multiple climate proxy records. (c) Overlap of the published multi-decadal time scale uncertainty ranges of all temperature reconstructions, with temperatures within 1 standard error (SE) of a reconstruction scoring 10%, and regions within the 5 to 95% range scoring 5% (the maximum 100% is obtained only for temperatures that fall within 1 SE of all 10 reconstructions). The HadCRUT2v instrumental temperature record is shown in black. All series have been smoothed with a Gaussian-weighted filter to remove fluctuations on time scales less than 30 years; smoothed values are obtained up to both ends of each record by extending the records with the mean of the adjacent existing values. All temperatures represent anomalies (C) from the 1961 to 1990 mean. (AR4 - Fig. 6.10)

CLIM 690: Scientific Basis of Climate Change Figure 6.12 THE LAST MILLENIUM - SH Temperature reconstructions for regions in the SH: two annual temperature series from South American tree ring data; annual temperature estimates from borehole inversions for southern Africa and Australia; summer temperature series from Tasmania and New Zealand tree ring data. The black curves show summer or annual instrumental temperatures for each region. All tree ring and instrumental series were smoothed with a 25-year filter and represent anomalies (C) from the 1961 to 1990 mean (indicated by the horizontal lines). (AR4 - Fig. 6.12)

CLIM 690: Scientific Basis of Climate Change Figure 6.13 THE LAST MILLENIUM - MODELS Radiative forcings and simulated temperatures during the last 1.1 ka. Global mean radiative forcing (W m 2 ) used to drive climate model simulations due to (a) volcanic activity, (b) solar irradiance variations and (c) all other forcings (which vary between models, but always include greenhouse gases, and, except for those with dotted lines after 1900, tropospheric sulphate aerosols). (d) Annual mean NH temperature (C) simulated under the range of 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 forcings and temperatures are expressed as anomalies from their 1500 to 1899 means and then smoothed with a Gaussian-weighted filter to remove fluctuations on time scales less than 30 years; smoothed values are obtained up to both ends of each record by extending the records with the mean of the adjacent existing values. (AR4 - Fig. 6.13)

CLIM 690: Scientific Basis of Climate Change Figure 6.14 NATURAL VS. ANTHROPOGENIC Simulated temperatures during the last 1 ka 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). 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. (AR4 - Fig. 6.14)

CLIM 690: Scientific Basis of Climate Change Figure 6.15 AEROSOLS Sulphate (SO 4 2 ) concentrations in Greenland (red and blue lines) and Antarctica (dashed violet) ice cores during the last millennium. Also shown are the estimated anthropogenic sulphur (S) emissions for the NH (dashed black). The ice core data have been smoothed with a 10-year running median filter, thereby removing the peaks of major volcanic eruptions. The inset illustrates the influence of volcanic emissions over the last millennium and shows monthly sulphate data in ppm as measured (green), with identified volcanic spikes removed (black, most recent volcanic events were not assigned nor removed), and results from the 10-year filter (red). The records represent illustrative examples and can be influenced by local deposition events. (AR4 - Fig. 6.15)

CLIM 690: Scientific Basis of Climate Change Box 6.3, Figure 1 GLACIER RETREAT Timing and relative scale of selected glacier records from both hemispheres. The different records show that Holocene glacier patterns are complex and that they should be interpreted regionally in terms of precipitation and temperature. In most cases, the scale of glacier retreat is unknown and indicated on a relative scale. Lines above the horizontal line indicate glaciers smaller than at the end of the 20th century and lines below the horizontal line denote periods with larger glaciers than at the end of the 20th century. The radiocarbon dates are calibrated and all curves are presented in calendar years. (AR4 - Box 6.3, Fig. 1)

CLIM 690: Scientific Basis of Climate Change Box 6.4, Figure 1 The heterogeneous nature of climate during the Medieval Warm Period is illustrated by the wide spread of values exhibited by the individual records that have been used to reconstruct NH mean temperature. These consist of individual, or small regional averages of, proxy records collated from those used by Mann and Jones (2003), Esper et al. (2002) and Luckman and Wilson (2005), but exclude shorter series or those with no evidence of sensitivity to local temperature. These records have not been calibrated here, but each has been smoothed with a 20-year filter and scaled to have zero mean and unit standard deviation over the period 1001 to 1980. (AR4 - Box 6.4, Fig. 1)

CLIM 690: Scientific Basis of Climate Change Milankovitch cycles

CLIM 690: Scientific Basis of Climate Change 1 ka

CLIM 690: Scientific Basis of Climate Change 1870-1990 (C20)

clim 690: scientific basis of climate change paleoclimate jim kinter18 feb 2010 ipcc working group...

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