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SOAR 2005 Past Climates and Current Changes Past Climate Records Instrumental 18th – 21st centuries with increasing accuracy Best in Europe, N. America, Australia Very little data over oceans, 70% of surface Keening Curve: 1957 - present CO2 in air over Mauna Loa, Hawaii Northern Winter: CO2 builds up from decay. Northern Summer: Plants absorb CO2 This simple curve started the whole damn controversy!! Past Climate Records Anecdotal Records Written records of planting, blooming, harvests Frozen Dutch canals in art Archeological sites Vikings in Greenland and Labrador Past Climate Records Proxy (indirect natural) Records Tree rings Temperature, precipitation, fire, insects, other stresses Depends on area, species level of stress best near stress limit Back to ~1000 years (bristlecone pine in CA) plus overlapping with structures Past Climate Records Proxy (indirect natural) Records Tree rings Fossil forests in the arctic … 60 million years old! Past Climates Proxy (indirect natural) Records Palynology (pollen) from sediments shrub Accumulated in peat bogs & lakes Must be independently dated (cross-matched or 12C) Local influences complicate records eg. Fire, flood, etc. Types of pollen vary in uniqueness eg. Pine pollen everywhere … even ice caps! birch sedge spruce oak Pine Past Climates Collecting sediment samples in Canada Lake sediments Peatland cores Dr. Steve Robinson, SLU Geology Past Climate Records Proxy (indirect natural) Records Ice Cores Alpine glaciers Greenland ice sheet Antarctic ice sheet Greenland ice sheet at 10,400 feet = 1.98 miles Past Climate Records Vostok & Greenland Ice Cores Show annual* variations of atmosphere Bubbles of air contain old atmosphere Variations in CO2, CH4 Give Comparisons to today, Correlations with temperature Ice crystals vary in composition Different Isotopes of Oxygen, Hydrogen, etc. Dust Volcanos, Impacts, Winds, Organic Matter *Where annual layers unclear, chronology is reconstructed from other annual variables (eg. Berillium in Isotopes Number of neutrons in nuclei varies eg. Oxygen 16 (16O) & 18 (18O) 16O 8 protons 8 neutrons 18O 18O 8 protons 10 neutrons heavier than 16O 1 18O in 1000 16O harder to evaporate Ice Cores High ratio of 18O/16O for warm globe Deep Sea Sediments High ratio of 18O/16O for cool globe Ice Core Data Isotopes indicate glaciations Ice Core Data Annual Layers Dating & N-S correlation 18O/16O GISP2 = Greenland Vostok = Antarctica Greenland ice core: arrows indicate summers. Isotopes Correlate with temperature Ice rich in heavy isotope indicates a warmer ocean Trapped air Atmospheric composition 2H/1H Ice Core Data Isotopes & Temperature Difference from current gives temperatures in past 18O/16O GISP2 = Greenland Vostok = Antarctica 2H/1H Ice Core Data Composition Correlation of temperature (isotopes) with CO2 and CH4 content Difference from 1996 over 150,000 yr Mostly much cooler: Ice Ages! Global CO2 CO2 from Ice Cores & Mauna Loa Carbon Dioxide Long-term sources: Volcanoes Long-term sinks: Chemical Weathering H2O + CO2 H2CO3 H+ + HCO3 Carbonic Acid CaCO3 + H+ Ca + HCO3 Variable storage: Biosphere Bicarbonate can combine with many compounds eg. NaHCO3, Ca(HCO3)2 CO2 Concentration plants absorb decay releases Relative Temperature Climate History Crowley “Remembrance of Things Past” Last 1000 Years Temperature Changes from 1900 level. Seems to be Northern Hemisphere only. Climate History Last 18ky Wisconsonian Glaciation Younger Dryas: Gulf Stream shutdown due to glacial meltwater flood down St. Lawrence River. Climate History Last 150ky mostly ice core data Climate History Last 140 ky Climate History Last 800ky Deep sea cores, 16O/18O Repeating ice ages much cooler than today! Humans Climate History Last 100My Marine & Terrestrial data Dinosaurs Much warmer in Mesozoic! ice ages Chicxulub Impact Impact Craters on Earth Slowly erased by erosion Fractured rock, gravitational variations indicate ancient craters World Impact Craters Chicxulub Impact Demise of the dinosaurs? Mapped by gravitational anomalies On Edge of Yucatan Peninsula Earth c. 65 million BCE http://www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/Chicx_title.html Impacts Cause of mass extinctions? Cause of climate change Variations in the Atmosphere Atmospheric Oscillations El Niño Southern Oscillation (ENSO) Trade winds slacken, warm water sloshes east Rain in Peru, Drought in Oceania, Varies elsewhere Pacific Decadal Oscillation (PCO) Latitude of warm pool varies Deflects positions of Jet Streams (storm tracks) Variations in the Atmosphere Atmospheric Oscillations Northern Atlantic Oscillation Strength of westerlies between 40°N and 60°N Driven by Azores/Iceland pressure difference Positive larger difference Recent positive phase unprecedented in last 500 years Negative smaller difference Positive Negative Variations in the Atmosphere Cool NAO Known since 19th Century Positive strong Gulf Stream warm winter & spring in Scandinavia & E. US cool along east coast of Canada & west Greenland Positive: Strong westerlies Warm Negative – dry in E. N.Am, wet in S. Europe Negative: Weak westerlies Variations in the Atmosphere Atlantic Oscillation Relation to NAO? Varies over days Mostly in positive mode recently Positive: Strong circumarctic winds trap cold air near pole Negative: Weak winds allow polar air to move south Variations in the Atmosphere Atmosphere/Ocean Connections Atlantic Multidecadal Oscillation Greenland icecores show oscillations 80 & 180 year variations in N. Atlantic temperature Driven by NAO? Positive NAO strong westerlies across Labrador sea cool ocean strengthens Gulf Stream & Thermohaline Circulation (THC) Negative NAO weak westerlies across Labrador sea keep ocean warmer weakens Gulf Stream & THC THC: Thermohaline Circulation Great Conveyor Belt moving HEAT circuit ~ 2000 years Variations in the Atmosphere Insolation Variations Solar brightness variations sunspots & other stellar variations Earth orbital variations other planets’ gravity vary Earth’s orbit Solar system environmental variation moves through galactic environment Spaceship Earth Galactic Environment Solar system passes through nebulae Spaceship Earth Sun is a variable star Solar constant ≈ 1370 W/m2 … varies stars evolve, luminosity varies early sun ~ 25% -30% dimmer than today Sunspot Cycle 11 year number cycle 22 year polarity cycle Earth gets more energy from sun when sunspot numbers are high. The Sun Sunspots Magnetic Hernias Sun’s equator rotates faster than poles Magnetic Field wraps up, bulges up Observed since 1611 (Johann Fabricius) Sunspots Discovered by Johann Fabricius Observed by Galileo Sol 04/09/04 Sunspots Number observed since 1611 Regular 11-year cycle Maunder Minimum Maunder Minimum Associated with Little Ice Age Began due to solar cooling Continued due to ice albedo effect Spaceship Earth Current Orbit moderates seasons Northern Summer at Aphelion mostly land, less solar flux reduces heat Southern Summer at Perihelion mostly water, more solar flux absorbed by oceans Perihelion: 1/2/5 r = 147.1 Gm Aphelion: 7/5/5 r = 152.1 Gm Variations in Earth’s Orbit Orbits characterized by eccentricity (ovalness) inclination (axial tilt) precession (axial wobble) All change due to gravitational influence of sun, moon & other planets Precession – 140 BCE by Hipparchus Eccentricity & Tilt Back 100,000 years – 1843 by Leverrier Back 1 million years – 1904 by Pilgrim Milankovitch Cycles Insolation changes with orbital variations Axial Tilt: 41,000 year cycle Makes seasons more or less severe Precession: 26,000 year cycle Changes season of perihelion Now: perihelion in early January Southern summer when Earth closes to sun Eccentricity: 100,000 year cycle Changes severity of seasons distance to sun varies more through the year Do Ice Ages correlate with orbit? Milankovitch Cycles Variation in Earth’s orbit due to gravitational attractions of other planets Eccentricity 100,000 years Currently 3% difference in distance 7% difference in insolation At Maximum, 9% difference in distance 20% difference in insolation Precession 23,000 years Changes season of perihelion Northern seasons much more severe more insolation on land masses in summer less insolation on land masses in winter Obliquity 41,000 years Axis Tilt Now: 23.5º Minimum: 22.5º Tropics closer to equator, Circles closer to poles Poles get less summer insolation (glaciation?) Equator gets more insolation (shallow angles at solstices) Maximum 24.5º Tropics farther from equator, Circles farther from poles Poles get more summer insolation (melting?) Equator gets less insolation (steeper angles at solstices) Insolation Varies with Milankovitch Cycles Calculation for 65 N (Berger (1991)) 9,000 years ago, ice age ended! Some argue this is the cause of all climate change … so we can ignore our CO2 Predicting the Future Climate Systems Atmosphere – changes over hours Oceans – surface changes over weeks – depths change over millennia Biosphere – changes annually to centuries Cryosphere – ice, glaciers permafrost, snow – various change scales Geosphere – volcanos, continental drif – long time scales, large changes Modeling the Climate Systems & Feedbacks Among Radiation insolation (incoming sunlight varies) reflection, absorption, re-radiation by surface, air Water cycle evaportion, precipitation, runoff Land surface soil moisture, vegitation, topography, snow & ice Ocean surface currents, deep currents, chemistry (salinity) Sea Ice strongly affected by feedbacks Feedbacks Positive Any change leads to further change eg. Ball on a hill Negative System always returns to equilibrium eg. Ball in a bowl Neutral System stays in new state eg. Ball on a plain Feedbacks Greenhouse Effect: Warming Good … makes Earth inhabitable!! Ground absorbs sunlight Ground heats (parking lots in summer) Ground radiates heat (Infrared, IR) Atmosphere absorbs (some) IR Atmosphere heats Feedback Mechanism: Evaporation Clouds shade surface, cool it, warming stops? H2O vapor absorbs more IR warming increases? Runaway Greenhouse … Venus! Feedbacks Greenhouse Effect: Warming Feedback Mechanism: Plant Growth More CO2 increases plant growth Plants absorb CO2 (Keeling curve annual cycles) CO2 is Reduced BUT … why isn’t it working yet? More CO2 increases plant growth More plant growth is good!! (Greening Earth Society of Western Fuels Assn.) Feedbacks Ice-Albedo Effect: Warming Warming melts glaciers, sea ice Ground warms more than snow/ice Ground warms, radiates more IR Atmosphere warms More ice melts Feedback Mechanism: Evaporation More water available More clouds & cooling, snow comes back H2O vapor absorbs more IR, more warming “Hot House Earth” Feedbacks Ice-Albedo Effect: Cooling Cooling causes more snow Snow reflects sunlight Ground cools, radiates little IR Atmosphere cools Snow doesn’t melt More precipitation falls as snow Feedback Mechanism: Ocean absorbs CO2 CO2 builds up over icy world, warming starts “Ice House Earth” IPCC Intergovenmental Panel on Climate Change View of the bulk of the scientific community Computer models estimate feedbacks Reports every 5 years 2005 report in draft form (www.ipcc.ch) “Hockey Stick” plot of temperature Third Assessment Report 2001 The Skeptics Important voices! Skeptics keep science honest Agreements CO2 in atmosphere is increasing CO2 levels correlate with temperature Arguments Climate is driven exclusively by insolation Milankovitch Cycles Sunspot Cycles Too expensive to reduce CO2: Adapt Global warming is good! What to Do? Complex system hard to model Experts don’t agree Could be global disaster Ignore it? Adapt? Mitigate it? Kyoto + ?