Transcript Green House Effect and Global Warming

Are We Getting Warmer?
Is the Earth getting warmer?
1. Yes
2. No
Is change in the Earth’s climate mostly
caused by natural causes or by
humans?
1. Natural causes
2. Humans
How do you measure a planets
temperature?
 If you have them, then
thermometers spread
around the earth can
tell us the average
temperature.
 These record go back
to the mid 19th century.
 Earlier records not
standardized so they
have more uncertainty.
What affects individual
temperature measurements?
1. Geographic
variations
2. Local
microclimates
3. Land use/heat
islands
4. Technique
5. Land or sea
6. All of the above
17%
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17%
2
17%
17%
3
4
17%
5
17%
6
 Records must account for sea surface
temperature, heat islands around cities, land
use changes, measurement techniques.
 Thermometers may differ in calibration.
 Look for trends in temperature rather than
absolute temperatures.
 Usually want to determine anomalies rather
than absolute values.
 Anomalies are deviations from average
temperature.
Regional Patterns
 Warming is greater on land than in oceans
(specific heat)
 Warming is larger in northern hemisphere
(more land and more GHG)
 Arctic has warmed at twice the global rate
– Ice-albedo feedback,
– lower evaporation; more energy directly to the
surface
Regional Temperature Anomlies
Zonal Mean Temperature Anomolies
Is the temperature rise unusual?
 Before 1850 we have very little direct
thermometric data so we use “proxies” for
measuring the temperature from long ago.
 Examples: tree rings, lake sediments,
bleaching of coral reefs, isotope ratios
Temperature for 1000 years.
Greenland Ice Cores
CO2 and Temperature are strongly
correlated.
 Probably not cause and effect.
Correlation
 Chronological relationship between two
factors
 Expressed as a number between -1 and 1
 Does not prove causal relationship
– Rising of Sirius  flooding of the Nile
– Coming to physics class  falling asleep
CO2 and Temperature are strongly
correlated.
 Probably not cause and effect.
 Small chances in temperature are caused
by small orbital changes.
 Small increase in sea surface temperature
causes some CO2 to come out of solution.
 Increase in land surface temperature
increases microbial action  more CO2
 More CO2 in the air cause further warming.
 Using Isotope ratios we can go back
millions to billions of years to find
temperatures.
– 16O vs. 18O
– 1H vs. 2H
 Compare ratios in different layers of ice.
 Arctic yields clearer results.
Evidence for Rapid Temperature
Changes in Greenland Ice Core
Younger Dryas
 The Big Freeze
 Approximately 15,000 years ago; 1300 year
duration
 Caused by collapse of North American ice
sheets(?)
 Believed to be nonlinear effects due to
changes in ocean circulation when there
was a large influx of fresh water from glacial
melting
Ocean Currents
 Caution: The rapid fluctuation in the
Younger Dryas are Arctic temperatures
which exaggerate global climate changes.
 Fluctuation not so obvious in proxies from
other regions of the world.
 The rapid changes that we are experiencing
now are global. They are also more
exaggerated in the polar regions.
Reduction in Sea Ice
1979-2005
Decline in Sea Ice
 Not only is there
less area of sea
ice, it is also
thinner.
Melting Glaciers
Global Warming Indicators
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Global temperature
Ice sheets (Greenland, Antarctic)
Arctic sea ice
Glaciers
Ocean surface temperature
Sea level
Is the Warming Anthropogenic?
Chicago Tribune
31 March 2006