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Period 14 Solutions: Climate Change
14.1 The Enhanced Greenhouse Effect
1) The Greenhouse Effect
a)
What is the cause of the enhanced Greenhouse Effect?
Gases in the atmosphere, such as water vapor, carbon dioxide,
methane, and CFC’s (from Freon and aerosol propellants) , allow
incoming visible light from the Sun to pass through to the Earth.
However, these gases absorb infrared radiation emitted by the Earth.
b)
What is the result of the enhanced Greenhouse Effect?
More outgoing infrared radiation is blocked by green house gases. The
result is a rise in the average global temperature.
c)
According to the graph of temperature variation, by how many degrees has the
average global temperature changed in the past 150 years?
by a little over one degree Celsius.
d)
What could account for this change in temperature?
Carbon dioxide added to the atmosphere from the complete
combustion of fossil fuels.
e)
What is the percent increase in atmospheric carbon dioxide between 1750 and
1996?
1750 = 275 parts per million (PPM)
1996 = 365 PPM
365 – 275 = 90 = 0.33 = 33%
275
275
2) Natural Climate Variations
a)
What three factors cause 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.
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b)
These three factors combined are known as Milankovitch cycles. What is the
result of Milankovitch cycles on global climate?
The Earth has experienced cycles of warming and cooling over
thousands of years. The Milankovitch cycles correspond to glacial ice
ages.
c)
Group Discussion Question: Is it likely that the recent rise in global temperature
is the result of a Milankovitch cycle?
No. The last warming cycle reached a maximum about 10,000 years
ago. The Earth has been in a long-term cooling trend for the past
6,000 years.
14.2 Evidence of Past Climate Conditions
3) Tree Rings as Evidence of Past Climate
a)
How can tree rings indicate past environmental conditions?
Each ring represents one year of tree growth during. A wider ring
indicates more growth and correlates to more precipitation and
moderate temperatures. Tree rings may also indicate environmental
events, such as drought, fire, or volcanic eruptions.
b)
c)
Examine the rings in the slice of tree trunk. This tree was felled in Columbus in
2012. Can you correlate the rings with the average precipitation in Columbus
over the past 15 years?
Do the variations in the tree’s rings represent changes in climate, in weather, or
in both weather and climate?
Only changes in the weather. Climate changes over decades and may
include variations in weather that are in the opposite direction of a
trend in climate change.
d)
Data from tree rings can approximate environmental conditions hundreds of
years ago using the method of cross matching. Each strip of tree rings
represents data from one tree.
i) Look for patterns in the tree rings that indicate an unusual pattern (several
years of drought, etc).
ii) Match these patterns across several trees so that your tree ring data covers
the life span of multiple trees.
iii) How many years of consecutive data can you assemble?
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4)
Ice Cores as Evidence of Past Climate
a)
b)
Examine an ice with a magnifying lens. What do you see within the ice?
Bubbles of air and possibly solid particles.
What information about past climate could be determined by their analysis?
Air bubbles give data on composition and concentrations of
atmospheric gases. Solid particles may contain fossil pollen that
indicates the species of plants in the region – indicator of temperature
and precipitation.
c)
Ice cores collected by the OSU Byrd Polar Center and other researchers provide
data on climate more than 100,000 years ago. Why is there an urgency to
continue collecting and storing ice cores?
Once glaciers have melted, this valuable source of information about
past climates will be lost.
5)
Oxygen Isotope Concentrations as Evidence of Past Climate
a)
What is the difference between the two isotopes of oxygen: oxygen-16 and
oxygen-18?
The nuclei of Oxygen-16 atoms consist of 8 protons and 8 neutrons.
Oxygen-18 nuclei have 8 protons and 10 neutrons.
b)
Which isotope is heavier?
Oxygen-18 because it has two more protons than oxygen-16
c)
Water with which isotope evaporates from sea water more easily?
Oxygen-16 because it is lighter than oxygen-18
d)
When in the form of water vapor, which isotope diffuses more readily over land
surfaces?
Oxygen-16 because it is lighter than oxygen-18
e)
Group Discussion Question: Looking at the globe on your table, imagine water
vapor containing both oxygen-16 and oxygen-18 evaporating near the equator.
Global convection currents cause this warm air to rise to the Earth’s poles.
i) Water with which isotope will condense and precipitate first in the
middle latitudes?
Oxygen-18 precipitates first because it is heavier than
oxygen-16
ii) Water with which isotope will be more likely to condense and
precipitate near the poles?
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Oxygen-16. Much of the oxygen-18 will have already condensed
and precipitated.
iii) Imagine this is a cooler glacial age, when the water that precipitates
near the poles remains there, locked in ice. What will happen to the
usual ratio of oxygen-16 to oxygen-18 in sea water?
With more oxygen-16 locked up in ice near the poles, the
concentration of oxygen-18 in sea water will rise above the
usual ratio.
iv) How can this ratio be used to determine past global temperatures?
Analyzing the shells of microscopic fossil sea life, such as
foraminifera, indicates the ratio of O-16 to O-18 when the shell
was formed. This ratio gives information on the average
temperatures at this time.
14.3 Consequences of a Warming Global Climate
6)
Cloud Formation
a) What are clouds made of – water vapor, water droplets, and/or ice?
Clouds consist of tiny water droplets or ice crystals (especially in higher
cirrus clouds). Clouds are not made of water vapor, which is invisible.
b) Why do clouds form?
As air rises, it cools. This causes the water vapor in the air to condense
into droplets.
c) Why does moisture form on the outside of a cold can of soda? Where does the
moisture come from?
Water vapor in the air is cooled in the vicinity of the can. The cooled
vapor condenses on the outside surface of the can.
d) As the Earth warms, more water vapor will evaporate from the seas.
i) What effect will increasing water vapor in the atmosphere have on global
temperatures?
More water vapor, a greenhouse gas, means a greater enhanced
greenhouse effect and warmer temperatures.
ii) Does this represent a positive or negative feedback loop? Positive because
the more water vapor added to the atmosphere, the greater the
increase in temperature.
e)
Some of the increased water vapor in the atmosphere will condense into liquid
water droplets and form clouds.
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i) What effect will condensed water vapor in the mid-level layers of atmosphere
have on global temperatures?
Water droplets in the atmosphere reflect incoming solar radiation back
into space. Less visible light reaches the Earth’s surface to warm it.
ii) Does this represent a positive or negative feedback loop?
Negative because the more condensed water vapor in the atmosphere,
the less radiation reaches the Earth, so warming decreases.
7)
Melting Polar Ice Sheets
a) What is the likely effect on the environment of melting ice sheets, such as those
in Antarctica and Greenland?
Sea levels are likely to rise.
b) As the temperature warms and melting accelerates, more liquid water will
evaporate into the atmosphere. What negative feedback loop in the process of
melting ice sheets is likely as more water vapor enters the atmosphere?
As more water vapor enters the atmosphere and condenses, more
precipitation will fall to Earth, including on the surfaces of ice sheets,
adding to the ice pack. This is negative feedback with respect to the
process of melting ice sheets. (Estimates indicate that the additional
precipitation rate will not exceed the melt rate and the ice sheets will
eventually melt.)
8)
Ocean Circulation
a) What effect does the Gulf Stream have on the climate of northern European
countries, such as the United Kingdom?
The Gulf Stream brings warm water from the tropics to northern
Europe and moderates the climate of the United Kingdom.
b) Why does the Gulf Stream water in the north Atlantic sink below the ocean
surface?
As the Gulf Stream water evaporates, it becomes saltier and denser.
The denser water sinks below the surface.
c) Where does this Gulf Stream water go? Where does it end up?
The Gulf Stream water flows southward through the Atlantic Ocean
and then eastward toward the Pacific. The water circulates through
the Pacific Basin, flows west, and ends up where it began, in the
southern Atlantic Ocean.
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d) What could happen to the ocean circulation if large amounts of fresh water from
melting ice sheets enter the north Atlantic Ocean?
Large amounts of fresh water could dilute the saltiness of the Gulf
Stream until it no longer is dense enough to sink. This would stop the
circulation of ocean currents.
e) What would be the result for our global climate?
The circulation of ocean currents ended temporarily about 12,000
years ago when massive quantities of fresh water were suddenly
released from Lake Agassiz in Canada into the northern Atlantic. The
result was an abrupt cooling of temperatures in the northern
hemisphere over the relatively short period of 70 years.
f) Group Discussion Do you think the Earth is a sensitive system – one that is
sensitive to changes in its initial conditions? Probably a sensitive system
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