WELCOME TO PERIOD 14:CLIMATE CHANGE Homework #13 is due today. Note: Homework #14 due on Thursday or Friday includes using a web site to calculate your carbon footprint. You should complete this homework before coming to class.
PHYSICS 1104 PERIOD 13 What is the result of the enhanced greenhouse effect on the Earth s climate? What is the evidence for past climates? What are some of the consequences of the climate change?
The greenhouse effect Greenhouse gas molecules in the atmosphere allow incoming shorter wavelength visible light to reach the Earth. These gas molecules block the outgoing longer wavelength infrared radiation emitted by the Earth. Greenhouse gases include carbon dioxide, methane, water vapor, and CFC s from freon and aerosol propellants.
Shorter wavelength visible light from the Sun can pass though the layer of greenhouse gas molecules. Longer wavelength infrared radiation emitted by the Earth is blocked by greenhouse gases. www.earthonlinemedia.com/ebooks/tpe_3e/energy/solar_and_earth_radiation.gif&imgref
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Variation from average temperature
Increase in atmospheric carbon dioxide Source: Dennis L Hartmann
Increase in atmospheric methane (CH 4 ) Source: Blunier et al. (1993) J. Geophys. Res. 20.
Variations in the Earth s motion Eccentricity of the Earth's orbit : The shape of the Earth s orbit varies from nearly circular to slightly elliptical with a cycle of about 413,000 years. Tilt of the Earth s axis: The tilt of the axis varies between 22.1 and 24.5 with a cycle of about 41,000 years. Precession of the Earth s axis: Changes in the direction of the Earth's axis of rotation relative to the fixed stars changes with a cycle of about 26,000 years. Source: http://en.wikipedia.org/wiki/milankovitch_cycles
Milankovitch cycles of climate change Milutin Milankovitch calculated climate cycles 100 years ago. The cycles explain the major ice ages every 100,000 and 41,000 years and minor cooling events every 19,000 to 23,000 years. Cooler summer temperatures prevented the winter snow from completely melting. Packed snow created miles thick glaciers covering large portions of the Northern Hemisphere. Source: Hays, Imbrie, Shakelton, 1976, Science
Milankovitch cycles and carbon dioxide Warmer air temperatures cause warmer ocean temperatures. Warmer sea water can dissolve less carbon dioxide. As water warms, more carbon dioxide from sea water is released into the atmosphere. The record of atmospheric carbon dioxide concentration reflects Milankovitch cycles of temperature variation.
Global temperature variation up to 1900
Global temperature variation up to 2000
Climate change evidence from tree rings In moderate climates, trees produce one ring of growth every year. The youngest growth is next to the tree bark. The width of the growth ring indicates the environmental conditions each year. A wider ring indicates greater precipitation and moderate temperatures. Source: //summitvoice.files.wordpress.com/2011/11/ tree_rings-v2.jpg
60 Annual Inches of Precipitation in Columbus, Ohio 55 50 45 40 35 30 25 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
Cross-matching and dating tree rings Matching patterns in ring width from tree samples allows combining data from multiple trees. Radio carbon dating: Identification of the exact year of ring formation can be done using radio carbon dating. Trees and other living organisms take in two isotopes of carbon: carbon-12 and carbon-14. Carbon-14 decays into carbon-12 with a half-life of 5,730 years. Every 5,730 years, one-half of the original cargon-14 has decayed into carbon-12. By measuring the ratios of carbon-14 to carbon-12, the number of half lives and the age of the object can be estimated.
Ice cores as evidence of past climates Glacial ice is deposited in annual layers. Annual rings, similar to the patterns in tree rings, define each year. The width of each ring indicates the amount of annual precipitation. Bubbles of fossil air in the ice show the content and concentration of gases in the atmosphere. Pollen in the ice indicates the plants living in the region. As glaciers melt, obtaining and storing ice cores from them becomes more urgent.
Example of data from ice cores Vostok ice sheet cores show the concentration of methane gas varies with the amount of incoming solar radiation. Solar radiation melts frozen surfaces and releases methane from the decay of organic materials.
Oxygen-16 and oxygen-18 isotopes Oxygen-16 atoms have 8 protons and 8 neutrons. Oxygen-18 atoms have 8 protons and 10 neutrons About 1 in 500 water molecules contain oxygen-18 The O-18 molecules are heavier. The O-16 water molecules evaporate more easily. Which molecule do you think diffuses more easily?
Oxygen-16 and oxygen-18 isotopes Convection currents transport water vapor from the tropics to the higher latitudes. O-18 water vapor condenses more easily. More O-18 condenses and precipitates in the lower latitudes. That leaves a higher concentration of O-16 molecules in the precipitation at high latitudes. During cold periods, when the O-16 remains locked in ice, sea water contains more O-18 than usual. The O-16/O-18 ratio in the shells of tiny marine animals (foraminifera) indicate sea temperatures. Source: http://en.wikipedia.org/wiki/file:benthic_foraminifera.jpg
Ocean current circulation
When ocean currents stopped. About 12,000 years ago, the ocean stopped circulating! Without the Gulf Stream to bring warm water from the tropics, northern temperatures dropped and ice sheets expanded. The cause? A massive input of fresh water from prehistoric Lake Agassiz in Canada. This fresh water decreased the ocean water s saltiness. The less dense water did not sink. This stopped ocean currents. Today, fresh melt water from the Greenland and Arctic ice sheets could dilute the saltiness of the Gulf Stream until it does not sink. Ocean currents might again stop.
BEFORE THE NEXT CLASS Read textbook chapter 15. Complete Homework Exercise 14. Print out Activity Sheet 15. Note: Homework #14 due on Thursday or Friday includes using a web site to calculate your carbon footprint. You should complete this homework before coming to class.