Download WELCOME TO PHYSICS 1103

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
//www.nps.gov/goga/naturescience/images/Greenhouse-effect.jpg
Variation from average temperature
Increase in atmospheric carbon dioxide
Source: Dennis L Hartmann
Increase in atmospheric methane (CH4)
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
Annual Inches of Precipitation in Columbus, Ohio
60
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.