- Slides: 67
SOAR 2007 Past Climates
Past Climates ü Climate History þ Types of records þ Climate reconstruction for Earth ü Climate variables þ Ocean/Atmosphere variations ý ENSO, PDO, NAO, AMO, Thermohaline circulation þ Events ý Volcanoes & Impacts þ Spaceship Earth ý Solar environment ý Galactic environment ý Orbital Variations
Past Climate Records ü Instrumental þ 18 th – 21 st centuries with increasing accuracy ý Best in Europe, N. America, Australia ý Very little data over oceans, 70% of surface þ Keening Curve: 1957 - present ý CO 2 in air over Mauna Loa, Hawaii Northern Winter: CO 2 builds up from decay. Northern Summer: Plants absorb CO 2 This simple curve started the whole damn controversy!!
Past Climate Records ü Anecdotal Records þ Written records of planting, blooming, harvests þ Frozen Dutch canals in art þ Archeological sites ý Vikings in Greenland Labrador
Past Climate Records ü Proxy (indirect natural) Records þ Tree rings ý Temperature, precipitation, fire, insects, other stresses ý Depends on area, species level of stress Ö best near stress limit ý Back to ~1000 years (bristlecone pine in CA) Ö plus overlapping with structures
Past Climate Records ü Proxy (indirect natural) Records þ Tree rings ý Fossil forests in the arctic … 60 million years old!
Past Climates ü Proxy (indirect natural) Records þ Palynology (pollen) from sediments shrub ý Accumulated in peat bogs & lakes ý Must be independently dated (cross-matched or 12 C) ý Local influences complicate records Ö eg. Fire, flood, etc. ý Types of pollen vary in uniqueness Ö 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 ü Proxy (indirect natural) Records þ Ice Cores ý Alpine glaciers ý Greenland ice sheet ý Antarctic ice sheet Greenland ice sheet at 10, 400 feet = 1. 98 miles
Past Climate Records ü Vostok & Greenland Ice Cores þ Show annual* variations of atmosphere ý Bubbles of air contain old atmosphere Ö Variations in CO 2, CH 4 Give ×Comparisons to today, ×Correlations with temperature ý Ice crystals vary in composition Ö Different Isotopes of Oxygen, Hydrogen, etc. ý Dust Ö Volcanos, Impacts, Winds, Organic Matter *Where annual layers unclear, chronology is reconstructed from other annual variables
Isotopes ü Number of neutrons in nuclei varies þ eg. Oxygen 16 (16 O) & 18 (18 O) 16 O 8 protons 8 neutrons 18 O 8 protons 10 neutrons 1 18 O in 1000 16 O þ 18 O heavier than 16 O harder to evaporate ý Ice Cores Ö High ratio of 18 O/16 O for warm globe ý Deep Sea Sediments Ö High ratio of 18 O/16 O for cool globe
Ice Core Data ü Isotopes indicate glaciations
Ice Core Data ü Annual Layers þ Dating & N-S correlation 18 O/16 O GISP 2 = Greenland Vostok = Antarctica Greenland ice core: arrows indicate summers. ü Isotopes þ Correlate with temperature þ Ice rich in heavy isotope indicates a warmer ocean ü Trapped air þ Atmospheric composition 2 H/1 H
Ice Core Data ü Isotopes & Temperature þ Difference from current gives temperatures in past 18 O/16 O GISP 2 = Greenland Vostok = Antarctica 2 H/1 H
Ice Core Data ü Composition þ Correlation of temperature (isotopes) with CO 2 and CH 4 content þ Difference from 1996 over 150, 000 yr Mostly much cooler: Ice Ages!
Global CO 2 ü CO 2 from Ice Cores & Mauna Loa
Carbon Dioxide ü Long-term sources: Volcanoes ü Long-term sinks: Chemical Weathering þ H 2 O + CO 2 H 2 CO 3 H+ + HCO 3 Carbonic Acid þ Ca. CO 3 + H+ Ca + HCO 3 ü Variable storage: Biosphere Bicarbonate can combine with many compounds eg. Na. HCO 3, Ca(HCO 3)2 CO 2 Concentration þ plants absorb þ decay releases Relative Temperature
Climate History ü Crowley “Remembrance of Things Past” ü Last 1000 Years Temperature Changes from 1900 level. Seems to be Northern Hemisphere only.
Climate History ü Last 18 ky Wisconsonian Glaciation Younger Dryas: Gulf Stream shutdown due to glacial meltwater flood down St. Lawrence River.
Climate History ü Last 150 ky þ mostly ice core data
Climate History ü Last 140 ky
Climate History ü Last 800 ky þ Deep sea cores, 16 O/18 O Repeating ice ages much cooler than today! Humans
Climate History ü Last 100 My þ Marine & Terrestrial data Dinosaurs Much warmer in Mesozoic! ice ages Chicxulub Impact
Ocean & Atmosphere Variations ü Pacific Ocean þ ENSO – El Niño Southern Oscillation þ PDO – Pacific Decadal Oscillation ü Atlantic Ocean þ NAO – North Atlantic Oscillation þ AMO – Atlantic Multidecadal Oscillation þ Atlantic Oscillation þ Thermohaline Circulation
Variations in the Atmosphere ü Atmospheric Oscillations þ El Niño Southern Oscillation (ENSO) ý Trade winds slacken, warm water sloshes east ý Rain in Peru, Drought in Oceania, Varies elsewhere þ Pacific Decadal Oscillation (PDO) ý Latitude of warm pool varies ý Deflects positions of Jet Streams (storm tracks)
Regional Current Variations ü PDO – Pacific Decadal Oscillation þ Currently in Positive phase (since April 2001) ý Fisheries in northeast pacific very productive
Variations in the Atmosphere ü Atmospheric Oscillations þ Northern Atlantic Oscillation ý Strength of westerlies between 40°N and 60°N ý Driven by Azores/Iceland pressure difference Ö Positive larger difference × Recent positive phase unprecedented in last 500 years Ö Negative smaller difference Positive Negative
Variations in the Atmosphere Cool ü NAO þ Known since 19 th Century þ Positive ý strong Gulf Stream ý warm winter & spring in Scandinavia & E. US ý cool along east coast of Canada & west Greenland Positive: Strong westerlies Warm þ Negative – dry in E. N. Am, wet in S. Europe Negative: Weak westerlies
NAO Mostly positive since mid 1970’s Mostly negative in ’ 40’s – ‘ 60’s www. jisao. washington. edu
Variations in the Atmosphere ü Atmosphere/Ocean Connections þ Atlantic Multidecadal Oscillation ý Greenland icecores show oscillations Ö 80 & 180 year variations in N. Atlantic temperature þ Driven by NAO? ý Positive NAO Ö strong westerlies across Labrador sea cool ocean Ö strengthens Gulf Stream & Thermohaline Circulation (THC) ý Negative NAO Ö weak westerlies across Labrador sea keep ocean warmer Ö weakens Gulf Stream & THC
NAO ü Negative Phase mid 1950’s - 1970
NAO ü Mostly positive since mid-70’s
Ocean Variations ü Atlantic Multidecadal Oscillation þ Sea Surface Temperature in North Atlantic
Ocean Variations ü Atlantic Multidecadal Oscillation þ Correlates with numbers of major hurricanes … and southwestern droughts! Not perfect correlation … what else is going on?
Ocean Variations ü Atlantic Hurricanes & ENSO þ Number & Strength of hurricane increases with La Niña
Variations in the Atmosphere ü Atlantic Oscillation þ Relation to NAO? þ Varies over days ý Mostly in positive mode recently Positive: Strong circumarctic winds trap cold air near pole Negative: Weak winds allow polar air to move south
THC: Thermohaline Circulation ü Great Conveyor Belt moving HEAT þ circuit ~ 2000 years
Climatic Events ü Volcanoes þ Put ash (SO 2) high in atmosphere ü Comet/Meteor Impacts þ Cause fires & tsunamis þ Put dust & ash high in atmosphere
ü Volcanoes Climatic Events þ Mt. Tambora, 4/5/1815 ý erupted after 5000 years of dormancy ý resulted in “year without a summer” in US In New England the summer of 1816 included … widespread frost at low level sites around New England on the 8 -9 th July and the damaging frosts on the 22 nd August from interior New England right the way south into North Carolina (Ludlum 1989). … This all led to crop failures and food shortages and helped stimulate a move westwards the following year. In both Connecticut and parts of New York State frosts after April are rare, but in 1816 frosts were recorded every month of the year (Lamb 1816, Neil Davids). http: //www. dandantheweatherman. com/Bereklauw/yearnosummer. html
Climatic Events ü Mt. Pinatubo, 6/15/1991 þ 10 times bigger than Mt. St. Helens In 1992 and 1993, the average temperature in the Northern Hemisphere was reduced 0. 5 to 0. 6°C and the entire planet was cooled 0. 4 to 0. 5°C. The maximum reduction in global temperature occurred in August 1992 with a reduction of 0. 73°C. The eruption is believed to have influenced such events as 1993 floods along the Mississippi river and the drought in the Sahel region of Africa. The United States experienced its third coldest and third wettest summer in 77 years during 1992.
Climatic Events ü Lots of Volcanoes þ Indonesia Krakatau may have split Sumatra from Java
Climatic Events ü Lots of Volcanoes þ Aleutian Islands Novarupta had largest eruption in 20 th Century on June 6, 1912 Redoubt ash 1990 Novarupta ash 1912 Spurr ash 1992 Augustine ash 1976
Climatic Events ü Ring of Fire … Pacific Rim
Climatic Events http: //www. volcano. si. edu /reports/usgs/
Impact Craters on Earth ü Slowly erased by erosion ü Fractured rock, gravitational variations indicate ancient craters World Impact Craters
Chicxulub Impact üDemise 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 ü Cause of mass extinctions? ü Cause of climate change Some may be due to nearby supernova explosions!
Recent Impacts ü Comet impact in 2800 BCE? þ Chevrons in Madagascar ý chevron-shaped piles of sediment from tsunami waves produced by comet impacts ý include deep ocean microfossils + impact debris http: //geology. com/news/labels/Oceanography. html
Recent Impacts ü Comet impact in 2800 BCE? þ Chevrons in Madagascar ý sea floor debris left by ancient megatsunami http: //geology. com/news/labels/Oceanography. html
Recent Impacts Chevrons Straight line on a spherical globe Crater? http: //maps. google. com/
Recent Impacts ü Comet impact in oceans þ Hard to find, indicated by chevrons http: //maps. google. com/
Variations in the Atmosphere ü Insolation Variations þ Solar brightness variations ý sunspots & other stellar variations þ Earth orbital variations ý other planets’ gravity vary Earth’s orbit þ Solar system environmental variation ý moves through galactic environment
Spaceship Earth ü Galactic Environment þ Solar system passes through nebulae Galactic year ~ 225 million years (Sol is 22) Sol crosses galactic plane every 33 Myr
Spaceship Earth ü Sun is a variable star þ Solar constant ≈ 1370 W/m 2 … varies ý stars evolve, luminosity varies ý early sun ~ 25% -30% dimmer than today þ Sunspot Cycle ý 11 year number cycle ý 22 year polarity cycle ý Earth gets more energy from sun when sunspot numbers are high.
Sunspots ü Magnetic Hernias þ Sun’s equator rotates faster than poles þ Magnetic Field wraps up, bulges up
ü Observed since 1611 (Johann Fabricius) Sunspots þ Discovered by Johann Fabricius þ Observed by Galileo Sol 10/03/07 04/09/04
Sunspots ü Number observed since 1611 Regular 11 -year cycle Maunder Minimum
Maunder Minimum ü Associated with Little Ice Age þ Began due to solar cooling þ Continued due to ice albedo effect
Spaceship Earth ü Current Orbit moderates seasons þ Northern Summer at Aphelion ý mostly land, less solar flux reduces heat þ Southern Summer at Perihelion ý mostly water, more solar flux absorbed by oceans Aphelion: 7/5/5 r = 152. 1 Gm Perihelion: 1/2/5 r = 147. 1 Gm
Milankovitch Cycles ü Insolation changes with orbital variations þ Axial Tilt: 41, 000 year cycle ý Makes seasons more or less severe þ Precession: 26, 000 year cycle ý Changes season of perihelion Ö Now: perihelion in early January Southern summer when Earth closes to sun þ Eccentricity: 100, 000 year cycle ý Changes severity of seasons Ö distance to sun varies more through the year ü Do Ice Ages correlate with orbit?
Milankovitch Cycles Variation in Earth’s orbit due to gravitational attractions of other planets
Eccentricity ü 100, 000 years þ Currently 3% difference in distance ý 7% difference in insolation þ At Maximum, 9% difference in distance ý 20% difference in insolation
Precession ü 23, 000 years þ Changes season of perihelion þ Northern seasons much more severe ý more insolation on land masses in summer ý less insolation on land masses in winter
Obliquity ü 41, 000 years þ Axis Tilt ý Now: 23. 5º ý Minimum: 22. 5º Ö Tropics closer to equator, Circles closer to poles Ö Poles get less summer insolation (glaciation? ) Ö Equator gets more insolation (shallow angles at solstices) ý Maximum 24. 5º Ö Tropics farther from equator, Circles farther from poles Ö Poles get more summer insolation (melting? ) Ö Equator gets less insolation (steeper angles at solstices)
Insolation ü Varies with Milankovitch Cycles þ 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 CO 2
Next Time ü Future climates & the IPCC 4 th Assessment http: //www. ipcc. ch/