Physical Geology 101
31. Climate Change
(p. 502-510; 568-590)
Weather and Climate
Weather is not the same as climate. The weather refers to __________________________________
___________________________________.
This involves changes in:
_______________________
_______________________
_______________________
_______________________
_______________________
Fluctuations in weather on the scale of hours, days, weeks, months, and years are totally natural.
What well-known natural influences on global weather, affecting global temperatures and rainfall and
causing billions of dollars in damage, are due to ocean current variations in the Pacific?
____________________
and
____________________
Over what time scale does this occur? _________________________
What is climate? _____________________________________________________________________
For example, the climate in equatorial areas is typically ____________________. The climate in areas
between 20-30° latitude is typically ________________________, producing deserts.
The regional climate of these areas may have a natural variability over the years, but there may also be
major changes in climate over longer periods of time. For example, the climate may get much cooler,
such as during an ice age, or it may get much hotter through a process called _____________________.
Example of a region where climate has changed greatly in the past 30,000 years:
_________________________ (used to have lush forests and high rainfall)
Long term climate changes may result in a region turning to desert. This process is called:
______________________________
Ice Ages
One of the obvious lines of evidence of global climate changes is the occurrence of ice ages in Earth's
past. The ice ages point to the global climate having been much cooler, so that the entire planet was
affected.
Ice ages have occurred at least 5 times in Earth's history and may last around a million years.
Examples of major ice ages:
______________________________ (~300 million years ago) – Karoo Ice Age
______________________________ (<1.6 million years ago) – Pleistocene Ice Age
What is the evidence for an ice age 300 million years ago? ______________________ (glacial rocks)
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Physical Geology 101
Over the past few million years, there have been numerous cycles of heating and cooling in global
climate.
How much do global mean temperatures need to drop for an ice age to occur?
__________________________
During the past 1.6 million years- the Pleistocene and Holocene epochs, there have been global lows in
temperatures on average every __________________ years.
How many cycles of ice ages occurred during the last ice age? ______________
What name is the last ice age known by? ____________________________
Less extreme variations in global temperatures occurred in cycles of about ___________________ years
during the ice age.
When did the most recent ice age end? _______________ years ago.
A period of warming in between ice ages is called an _________________________.
The warmest point in the current interglacial period was between 7,000 and 6,000 years ago. Since then,
it has been getting steadily WARMER or COOLER ?
There have been short-term variations such as between 1300 and the mid-1800s, when glaciers around
the world were advancing. This ~500 year period of cooling is referred to as the ___________________.
Right now, we seem to be on a warming trend within a longer time-scale cooling trend.
What regions were covered by ice sheets during the last ice age?
___________________, __________________, and _______________________
During an ice age, ice sheets expand in size but we never have the entire planet being covered in ice.
Only the coldest regions in the northern and southern hemispheres were ice-covered.
How thick were the Pleistocene ice sheets? _________________
How much of the Earth's surface did they cover? ___________
How much of the Earth's surface do ice sheets cover today? ____________
Changes in the size of ice sheets affect the climate in regions that are not covered in ice. As the ice
sheets expand, warm and moist regions get shifted towards the equator. So the warm, moist
Mediterranean climate got shifted southwards during the last ice age, into northern Africa. That’s why the
Sahara Desert region used to be much wetter.
Evidence for Ice Ages
The study of ancient climates is called _________________________.
There are several lines of GEOLOGICAL evidence for determining past climates:
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Physical Geology 101

________________________ - fossilized plants and animals can be related to specific types of
climate that such species would have inhabited.
Example: _______________________________

________________________ - sedimentary rocks can often be linked to specific depositional
environments, such as varve clays from glacial lake beds and tillite.

________________________ - ancient soils, also called __________________, have minerals in
them that tell us of the chemical conditions in ancient air and water that can be related back to the
temperature conditions.

_____________________________ - we can study the isotope ratios of elements like oxygen in
ancient sediment layers, corals, and ice cores drilled from deep in ice sheets to tell us about the
composition of the ancient atmosphere.

________________________ - the distribution of recessional moraines can tell us about the
extent of old ice sheets. (Example: ___________________________). Grooves on glacial
pavements can tell us the directions that glaciers were moving towards.

________________________ - there were large lakes that formed far from the glaciers during the
last ice age because of lower temperatures and less evaporation.
Example: ________________________________

________________________ formed along the edges of the ice sheets, dammed by glaciers.
Example: _______________________________
This glacial lake broke through its ice dam many times, causing huge floods that washed over N.
Idaho and E. Washington, forming the ____________________. The surface was stripped bare of
topsoil, basalt was heavily eroded. As the lake drained, _____________________, up to 10m high,
formed along the old lake bed.

________________________ - sea level was up to __________ lower during the last ice age
because of all the water taken up by glaciers. This caused major changes in stream channels,
and provided land bridges connecting areas of land that today are separated by water. This
allowed many species of animals to migrate into new areas.
Lowered sea level allowed many species of animals to migrate into new areas. A migration of
humans into ____________________ from _____________ was possible during the last ice age
because a land bridge extended across the Bering Strait between the two continents at that time.
Causes of Global Climate Change
What four types of geologic events may cause changes in global climate?
1. _____________________
2. _____________________ - time scale over which climate is affected: ____________________
3. _____________________
4. _____________________
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Physical Geology 101
Global climate changes that resulted from the Chicxulub meteorite impact on the Yucatan Peninsula,
Mexico, 65 million years ago resulted in the extinction of the dinosaurs.
When we look at the variations in global temperatures, there is an obvious cyclicity that suggests some
natural control on global climate variability over long time scales. This is related to changes in the Earth's
rotation and revolution about the sun over long periods of time.
First of all, the Earth does not have a perfectly circular and unchanging orbit about the Sun. Its orbit is
slightly elliptical, and changes shape over a time scale of about _________________. This phenomenon
is called ___________________.
Also, the inclination of the Earth's tilt, currently 23.5° from vertical, oscillates back and forth between 21.5°
and 24.5°, varying by about 1.5° every _________________.
The direction the rotation axis faces also wobbles about over a time scale of ________________. This
phenomenon is called ___________________.
These three effects cause changes of up to 10% in how much of the Sun's energy strikes the Earth at a
particular location. The changes are mathematically regular, and are known as:
______________________________________.
Which phenomenon is responsible for global climate changes on the:

20,000 to 40,000 year time scale:

100,000 year time scale:
PRECESSION
PRECESSION
or
or
ECCENTRICITY ?
ECCENTRICITY ?
Anthropogenic Influences on Climate
Since the Industrial Revolution, human activities (also called ___________________________________)
have resulted in a sharp increase in the amount of greenhouse gases emitted into the atmosphere.
These are the substances that tend to cause an increases in temperatures at the surface because they
absorb heat.
Examples: ____________________,
_____________________,
____________________________
The burning of fossil fuels like coal and petroleum has been a major cause of these increases.
There are naturally occurring greenhouse gases in the atmosphere, such as water vapor and naturally
occurring carbon dioxide and methane. These gases help keep the Earth's surface warm and habitable.
But anthropogenic greenhouse gases appear to be upsetting the balance.
In the past 100 years, global temperatures have risen by an average of _____°F (_____°C). Changes of
just a few degrees are enough to cause major climate changes, so this is an alarming trend. For example,
melting of glaciers would cause the Earth's ocean levels to rise by several meters or 10s of meters.
Flooding of coastal areas would be devastating, and low-lying regions like Florida, Netherlands,
Bangladesh, and the South Pacific islands could be eradicated.
FINAL QUESTION:
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Physical Geology 101
What is the projected temperature increase by 2100 if current trends continue?
_______________
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