Climate and Climatic Change
Climate Influences everything Housing -- where we live, heating/cooling Clothing -- what we wear Agriculture -- food supply and cost Flora and Fauna -- palm trees to tundra Lifestyle -- choice of activities Climate is defined as: (1) the aggregate of weather conditions over an extended time period (1970-2000) and (2) the frequency of extreme weather events (such as thunderstorms, tornadoes, hurricanes, lightning strikes, etc.)
Two Branches of Climatology Applied Older Explorers Geographers Empirical Descriptive Plant distribution Classification What
Theoretical Newer Meteorologists Climate Modelers Deductive Dynamic Physical principles Feedback Why
Climate Classification Vladimir Köppen (1918), father-in-law of Alfred Wegener. Pattern of world climate classifications still used today. Based on Temperature, Precipitation. Related to vegetation types A. Tropical rainy, cool month > 18o C B. Dry, desert C. Mid-latitude rainy, mild winter D. Mid-latitude rainy, cold winter E. Polar, warmest month < 10o C H. Highland, above 15,000 feet
Climate Dynamics (Air masses)
Climate Change
Evidence of Past Climates (Anthes fig. 7.9) 1. 2. 3. 4.
Remote sensing from satellites (since 1979) -- no change Instrumental surface record (since 1860) -- 0.6 C warming Diaries, written records of flood, harvest, ice (1 Ka) Proxy records Tree Rings or dendrochronology (100 - 5 Ka) Lake Cores, Packrat Middens (100 a - 10 Ka) -- sediments, varves, pollen, seeds, C14 (5730 a) Ice Cores (100 a - 100 Ka) -- CO2 bubbles, dust deposits, δ O18 Loess Deposits (100 a - 100 Ka) -- aeolean dust, strata Ocean Cores (1 Ka - 1 Ma) -- sediments, mud, Isotopes Sedimentary Rocks (1 Ka - 100 Ma) -- fossils, strata
C14 dating proxy Radioactive C14 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 C14 continues to decay. The older the organism, the less C14. δ O18 temperature proxy Both O18 and O16 are stable isotopes of oxygen Since O18 has two more neutrons than O16 water (H2O) containing O18 is heavier, harder to evaporate. As temperature decreases (in an ice age), snow deposits contains less O18 while ocean water and marine organisms (CaCO3) contain more O18 The O18 / O16 ratio or δ O18 in ice and marine deposits constitutes a proxy thermometer that indicates ice ages and interglacials. Low O18 in ice indicates it was deposited during cold conditions worldwide, while low O18 in marine deposits indicates warmth.
Milankovitch, Enhanced GH, Ocean circ.
Every star has an “ecosphere”
Warm and Cold Periods in Earth History
5 Billion BP (all of Earth history)
Mechanisms: Galactic dust , Evolution of the Sun, Evolution of the Atmosphere
180 million BP
Mechanisms: Evolution of the Atmosphere, Plate Tectonics, Mountain Building, Volcanic Activity, Solar Variability, Ocean Circulation
1 million BP
Mechanism: Orbital Parameters
120,000 BP
Mechanism: Orbital Parameters
James Croll(1821-1890) Leading proponent of an astronomical theory of climate change in the nineteenth century. Checquered 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.
Milutin Milankovitch (1879-1958) Leading proponent of an astronomical theory of climate change in the twentieth 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.
Ice Age (Pleistocene) 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 CO2 from atmosphere Cooling due to expanding ice caps and decreased CO2
Interglacial (Holocene) 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 CO2 to atmosphere Warming due to shrinking ice caps and increased CO2
Ice Age World: 18,000 BP
Thermohaline circulation
Interglacial Sea Level Greenland = 6 meters West Ant. = 5 meters East Ant. = 60 meters Human impacts are HUGE
Glacial Era Sea Level
Glacial-Interglacial Sea Level Changes
18,000 BP
1,000 BP
1870-1990