Chapter 14 Atmo 102

When was the last time North America was covered with ice sheets?
18,000-22,000 years ago
What is another name for ice sheets?
continental glaciers
What percentage of Earth’s land surface is covered by glaciers?
10%
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What are some methods of examining past climate events (geology)?
– core samples from ocean floor sediments
– ice cores from glaciers in Greenland and Antarctica
What evidence does geology tell us about past changes in climate?
suggests global climate has undergone slow but continuous changes
What are some chemistry methods of examining past composition of the atmosphere?
looking at bubbles of ancient air trapped in ice
– help determine CO2 concentrations
What role do isotopes play in climate event studies?
reconstructing past climate events
– use isotopic ratios
What are isotopes?
– same chemical element (same # protons and electrons but different # of neutrons)
– small differences in physical properties
Which two isotopes are important for climate studies?
O-16 (8 neutrons) and O-18 (10 neutrons)
O-18 and O-16 evaporation/condensation rates
O-18 evaporates more slowly and condenses more readily than O-16
Ratio of O-18 to O-16 during cold periods
increases
Ratio of O-16 to O-18 in the atmospheric water vapor during cold periods
increases
During cold periods isotopic ratios in ice vs. oceanic shells/sediments
– ice has higher O-16
– ocean has higher O-18
How much below normal does a T have to fall for an ice age to occur?
~8 degrees
GHG (CO2, methane, H2O vapor) levels during the last ice age compared to now
CO2: ~30% lower
methane: ~50% lower
H2O: lower
Sea level during last ice age compared to now
100-125m lower
What is the Younger Dryas?
period of rapid decrease in T
Positive feedback mechanism (assume Earth is warming) of water vapor
1) more evaporation from oceans
2) increase in water vapor in atm.
3) increase in IR absorption = strengthens GHE
4) T rises
If the positive feedback mechanism is not controlled what will happen?
Runaway GHE
Negative feedback (assume Earth is warming) moisture in the air
1) atmosphere warms/moistens
2) more low clouds
3) more reflection of solar radiation
4) decrease in solar heating of surface
5) slows warming
Milankovitch theory
describes climatic changes to variation in Earth’s orbit
First cycle of Milankovitch theory
*eccentricity*
– deals w/ changes in shape of orbit
Greater eccentricity means what?
more elliptical = greater variation in solar E received at the top of the atmosphere
What is our current eccentricity characterized as?
low
Second cycle of Milankovitch theory
*”wobble”*
-takes into account the Earth rotates on an axis
What is “wobble” defined as?
known as the precession of the Earth’s axis
– occurs in a cycle of about 23000 years
Third cycle of Milankovitch theory
*obliquity*
– changes in the tilt of the Earth as it orbits the sun
Current obliquity and variation range
current: 23.5 tilt
range: 22-24.5 degrees
If there is a low tilt what does that mean for seasonal changes?
less seasonal variation and less likely for glaciers to form
On top of the changes in Earth’s orbit what other factors contribute to climate change?
– amount of dust in the atm.
– reflectivity of ice sheets
– concentration of GHG’s
– changing characteristics of clouds
– ocean circulation
– glaciers melting
CLIMAP project
able to reconstruct the Earth’s ocean surface T in the past by examining sediments at the bottom of the ocean
Aerosols
tiny liquid and solid particles that enter the atmosphere
Effect of aerosols
complex; depends on particles size, shape, color and vertical distribution
How do aerosols enter the lower atmosphere?
via oceanic emissions of organic sulfur or anthropogenic sources
Direct forcing of aerosols
sulfate aerosols reflect incoming sunlight
*lowers Earth’s surface T during the day*
– cooling effect may be equal to warming induced by CO2
Indirect forcing of aerosols
sulfate aerosols may also modify clouds by increasing their reflectivity
Result of volcanic ash/particles being ejected into the stratosphere
– warming of stratosphere
– cooling of global surface air T
What are volcanic eruptions rich in sulfur result in?
warm the lower stratosphere
What role does CO2 play in the warming of the earth?
– strongly absorbs IR radiation
– major role in warming of the lower atmosphere
What impact will rising ocean T’s result in?
– increase in evaporation rates
– increase in atmospheric water vapor
What is a speculation of why the Younger Dryas occurred?
cutting off the Gulf Stream from the global ocean circulation “belt”
Possible consequences of doubling of CO2 from its present value
globe will warm between 1.5 and 4.5 degrees C
Since the beginning of this century the avg. global surface air has risen by?
0.3 and 0.6 degrees
Evidence that the warming is due to the GHG’s
– stratosphere cooled
– high latitudes warm more
– night warms more
Dendrochronology
study of annual growth rings of trees
desertification
an increase in the desert conditions of a region
Maunder minimum
refers to a time when there were few sunspots
Little Ice Age
cooling trend that occurred from 1550-1850
water vapor
most potent greenhouse gas
Ice Age
another name for the Pleistocene epoch
carbon dioxide
this GHG has doubled in concentration over the past 100 years are so
year without summer
another name for the year 1816
Volcanoes that have the greatest impact on global climate appear to be those rich in this gas:
sulfur
Climate models predict that in order for increasing levels of CO2 to raise air T’s between 2 and 5 degrees C, this gas must also increase in concentration:
water vapor
Overall, clouds have a net ____ effect on climate
cooling
If the Earth were in the warming trend, increasing the amount of water vapor in the atmosphere (but not clouds) would most likely produce a ____ feedback mechanisms
positive
A negative feedback mechanism:
weakens an initial change in an atmospheric process
Most climate models predict that a gradual increase in global CO2 over the next 100 years will most likely bring about:
an increase in surface air T
The theory that explains how glacial material can be observed today near sea level at the equator, even though sea level glaciers probably never existed at the equator, is the:
theory of plate tectonics
During the period when the earth’s orbital tilt is at a minimum, which would probably be true?
Less seasonal variation between summer and winter
The wobble of the earth on its axis refers to:
precession of the equinox
If the earth were in a cooling trend, what is an example of a positive feedback process?
Increasing the amount of cloud cover around the Earth
What are the possible consequences of global warming?
1) reduction in avg. precipitation over certain areas
2) cooling of upper atmosphere
3) drop in rate of ozone destruction
4) accumulations of additional snow in Antarctica
The warming trend in the NH could be the result of:
increasing levels of CO2 and other GHG’s
Climate models predict that the greatest warming due to increasing levels of GHG’s will most likely occur in
polar latitudes
The planet with the so-called runaway GHE is ?
Venus
It appears that throughout much of the Earth’s history, the climate was much cooler than it is today (T/F)
F
The Milankovich cycles, in association w/ other natural factors, explain how glaciers may advance and retreat over periods of ten thousand years to one hundred thousand years (T/F)
T
Most climate predict that if average global T’s rise by about 5 degrees F or more, the avg. global precipitation will increase (T/F)
T

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