Download Earth`s Climate System

Chapter 16: Earth’s Climate System
1. Want Ice with That?
2. Global Air Circulation
3. Global Climate Regions
4. Extreme Climate Environments
5. Records of Climate Change
6. Natural Causes of Climate Change
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Learning Objectives
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Students will explain concepts related to Earth’s climate systems.
Students will explain why areas with the same latitude have
different climates.
Students will summarize the features of the global climate regions.
Students will predict the climate for a location given rainfall and
temperature data.
Students will describe types of glaciers, glacial features, and
describe how glaciers are formed.
Students will analyze patterns in temperature and cloud cover,
precipitation, and air pressure and relate these patterns to Earth’s
deserts.
Students will identify the features of a desert.
Students will compare the action of glaciers with desert wind action.
Students will describe proxy indicators used to determine past
climates.
Students will explain natural causes of climate change.
Want Ice with That?
Each fall, polar bears
migrate through Churchill,
Manitoba on their way to
Hudson Bay to wait for new
sea ice to form so they can
hunt seals.
17% reduction in Hudson
Bay polar bears in past 30
years.
Rising temperatures in the
Arctic cause sea ice to melt
earlier in spring and form
later in fall.
Who is in more danger, the tourist
or the bear?
Bears hang around in
Churchill longer waiting for
the ice to form.
The Good Earth/Chapter 16: Earth’s Climate System
Want Ice with That?
Polar Bear
Jail, Churchill,
Canada.
Polar bears
that wander
into Churchill
are captured
by the trap
and placed in
"jail" until
Hudson Bay
freezes over.
The Good Earth/Chapter 16: Earth's Climate System
Want Ice with That?
Climate = A description of the weather conditions for a region
averaged over several decades.
The climate of every region on Earth has changed often.
Shrinking glaciers are just
one line of evidence of
increasing global
temperatures.
a. Riggs glacier, Glacier
Bay National Park, Alaska
in 1941.
b. Riggs glacier in 2004.
The Good Earth/Chapter 16: Earth's Climate System
Want Ice with That?
The Arctic – A prime example of a region recording climate
change
Signs of change:
Decline in polar bear
population
Rise in average
temperatures by 2-3°C.
This temperature rise is
more than double what is
observed throughout the
rest of the world.
Shrinking glaciers and
other ice masses.
Rising sea level and
increased coastal erosion.
The Good Earth/Chapter 16: Earth's Climate System
Want Ice with That?
• Widespread and steady decline in
Arctic sea ice over last few
decades.
• Puts cold water into Arctic ocean –
could disrupt the oceanic conveyor
belt.
• Worst case scenario:
- Higher temps reduce annual volume
of sea ice exposing more open
water in Arctic ocean
- Water has lower albedo which
absorbs more heat from sun
- Sea ice forms later in the fall and is
thinner and not as widespread;
melts earlier in spring
The Good Earth/Chapter 16: Earth's Climate System
Want Ice with That?
Process repeats – positive feedback loop
Each time the environment is modified it becomes less likely
that the warming will reverse itself
Worst case scenario continued:
- Melting of ice changes density and salinity of Arctic ocean
water
- Freshwater input from Greenland further dilutes salt content
- Reduction in sinking water at northern end of Gulf Stream
can slow the conveyor belt
- Temperatures in the North Atlantic can decrease with slowing
of Gulf Stream
The Good Earth/Chapter 16: Earth's Climate System
Want Ice with That?
Best Case Scenario:
- Temperature increase is a short-term variation, and lower
temperatures begin to prevail
- Sea ice volume increases, increasing albedo and reducing
absorption of heat
- Sea ice forms earlier in fall and stays around longer into
spring
- Sea water salinity increases with increasing sea ice
- Less melting of ice sheet on Greenland and elsewhere
- Temperatures in North Atlantic gradually decrease and return
to levels similar to those of the 1980's
This doesn't seem likely, as warming trend continues each
year. Eight of the ten hottest years on record have occurred in
the last decade. The Good Earth/Chapter 16: Earth's Climate System
Want Ice with That?
Why do we care?
The big question is –
ARE HUMANS AFFECTING CLIMATE
CHANGES?
The Good Earth/Chapter 16: Earth's Climate System
Earth's Climate System Self Reflection
Survey
Answer the following questions as a means of uncovering what
you already know about Earth's climate system.
1. Imagine that you were blindfolded and airdropped onto a continent somewhere on
Earth. What features could you use to
identify the climate of the region?
The Good Earth/Chapter 16: Earth's Climate System
Earth's Climate System Self Reflection
Survey
Answer the following questions as a means of uncovering what
you already know about Earth's climate system.
2. Any effective climate model must account
for regional variations in climate at any
moment in time as well as for variations in
climate for any location over the course of a
year. Make a list of what you know about
annual variations in climate in the U.S. and
around the globe.
The Good Earth/Chapter 16: Earth's Climate System
Earth's Climate System Self Reflection
Survey
Answer the following questions as a means of uncovering what
you already know about Earth's climate system.
3. What are some climate-related concepts
featured in earlier chapters of this text?
The Good Earth/Chapter 16: Earth's Climate System
Go back to the Table of Contents
Go to the next section: Global Air Circulation
The Good Earth/Chapter 16: Earth's Climate System
Global Air Circulation
Look at these four maps: What patterns do you see?
The Good Earth/Chapter 16: Earth's Climate System
Global Air Circulation
Several significant patterns should emerge:
• Temperatures decrease with increasing latitude north and south from
equator. Equator receives more solar energy.
• Temperature range is much greater for the continents than for the
oceans. Water has a high heat capacity.
• Clouds are concentrated in irregular bands parallel to the equator and
latitudes 60° N and S, and these latitudes also have high precipitation
and low atmospheric pressure. Desert belts are located around 30°N and
S latitude.
The Good Earth/Chapter 16: Earth's Climate System
Global Air Circulation
Non-rotating Earth model –
rising air at the equator and
sinking air at the poles would
form opposing limbs (loops) of
a large-scale circulation
pattern called a convection
cell.
Q: Where is there lowpressure and where is there
high-pressure?
A: Low-pressure where
air rises (equator) and
high pressure where air
descends (poles).
A difference in solar radiation causes
differential heating, which produces
convection cells that drive air circulation.
The Good Earth/Chapter 16: Earth's Climate System
Earth's Climate System Checkpoint 16.1
The following map shows the locations of four climate extremes.
Match each extreme climate with its location (each is only used
once).
a. Highest temperature (136°F) is at location _____
b. Highest average annual precipitation (524 inches) is at location _______
c. Second lowest temperature (-90°F) is at location ______
d. Lowest annual precipitation (0.08 cm) is at location ______
The Good Earth/Chapter 16: Earth's Climate System
Earth's Climate System Checkpoint 16.2
Florida lies at the same latitude as the
Sahara Desert. Why do you think Florida
is not a hot, dry desert?
The Good Earth/Chapter 16: Earth's Climate System
Global Air Circulation
The Earth rotates complicating the
system.
Regardless of Earth's rotation,
warm humid air expands and rises
at the equator, forming a lowpressure system and nearly
continuous band of clouds.
The Coriolis effect deflects winds
to the right in the Northern
Hemisphere and to the left in the
Southern Hemisphere.
North moving air is continuously
deflected east and is moving
almost directly eastward by the
time it reaches 30°N = Subtropical
Jet Stream
Jet stream moves in upper
troposphere at speeds
approaching 61 mph.
The Good Earth/Chapter 16: Earth's Climate System
Global Air Circulation
Descending air warms adiabatically
and its relative humidity decreases
promoting desert formation.
Trade winds – prevailing surface
winds deflected north and south at
these areas of descending air.
Hadley Cell – continuous convection
cell formed by columns of rising air
and descending air connecter by north
and south moving winds.
Polar Cell – anchored by a column of
descending air in the polar regions.
Ferrel Cell – midlatitude convection
system separating thermal circulation
cells - not as well defined, as they are
modified by midlatitude cyclone
formation.
The Good Earth/Chapter 16: Earth's Climate System
Global Air Circulation
Atmospheric circulation can be divided into three convection cells in
each hemisphere.
These bands of wind are often disrupted by variations in topography,
especially in the Northern Hemisphere.
Jet streams are
present near the top of
the troposphere.
Winds in the core of
the jet streams can
reach speeds of more
than 195 mph!
The Good Earth/Chapter 16: Earth's Climate System
Go back to the Table of Contents
Go to the next section: Global Climate
Regions
The Good Earth/Chapter 16: Earth's Climate System
Global Climate Regions
Climate regions are differentiated by their temperatures
and precipitation and their resulting vegetation.
Koppen-Geiger classification system uses average monthly temperatures
and precipitation, and total annual precipitation.
Averaging can cause microclimates to be missed.
The Good Earth/Chapter 16: Earth's Climate System
Earth's Climate System Conceptest
The following graph illustrates mean monthly high and low
temperatures and the average monthly rainfall for Sydney, Australia.
Estimate the average monthly temperatures as halfway between the
mean high and low temperatures. On the basis of these data, in what
climate region does Sydney belong? Explain your reasoning.
a. Tropical
b. Dry
c. Warm
temperate
d. Cool temperate
The Good Earth/Chapter 16: Earth's Climate System
Global Climate Regions
The Good Earth/Chapter 16: Earth's Climate System
Global Climate Regions
Ecosystems = communities of organisms that inhabit specific physical
environments.
Biodiversity = the number of species in an ecosystem.
Biome = a regional community of plants and animals named after the
dominant type of vegetation.
Humans, unlike other organisms, inhabit a wide range of biomes. Why?
The Good Earth/Chapter 16: Earth's Climate System
Global Climate Regions
What can you
say about the
relationship
between
population
density and
climate
regions?
Global population density. Darker colors signify
regions with highest population density.
In terms of altitude,
most organisms live
in a narrow vertical
band of land and
shallow sea where
the climate is warm
and moist.
The Good Earth/Chapter 16: Earth's Climate System
Earth's Climate System Checkpoint
16.6
How does the distribution of people on Earth
compare to the distribution of climate zones
and biomes?
hint: refer to figures 16.8, 16.9, and 16.11
The Good Earth/Chapter 16: Earth's Climate System
Global Climate Regions
Three major climate-related biome groups: grasslands, forests, and
deserts.
Each of these can be divided into individual biomes.
Tropical rain forests are a critical biome – dominate the tropical climate
region and are home to the most diverse ecosystems on the planet,
containing 50,000 plant species!
Changes in biome character can tell us about climate change.
Environmental factors
influencing the
distribution of
ecosystems. Why are
most species found in
the upper 200 meters of
the ocean and below
about 20,500 feet on
land?
The Good Earth/Chapter 16: Earth's Climate System
Global Climate Regions
Biogeochemical Cycles
Plants are
producers
Animals are
consumers
Food chain –
transfers
energy
between
organisms
within an
ecosystem
N, C, O, H, P,
S make up
95% of the
materials in
plants and
animals
Biomass = amount of organic material in
an ecosystem. Plants account for 99% of
all biomass on Earth.
The Good Earth/Chapter 16: Earth's Climate System
Earth's Climate System Checkpoint
16.8
With all the media reports about climate change, people in
your community turn to you to help them figure out if it is
really happening. They ask you to generate a common sense
index of climate change that could be used by long-time
residents (longer than 20 years) of your community. The
index should not be too complicated, so you must identify just
three things that an interested resident could observe, using
data from the evening news, the Internet, or a local
newspaper. Finally, residents should not have to collect daily
weather data, but they may be asked to compare daily data
with long-term averages. What three factors would you
choose and how would residents use them to identify climate
change?
The Good Earth/Chapter 16: Earth's Climate System
Go back to the Table of Contents
Go to the next section: Extreme Climate
Environments
The Good Earth/Chapter 16: Earth's Climate System
Extreme Climate Environments
What makes an environment extreme?
Exceptionally high or low temperatures and/or lack of precipitation
Where on this
map might you
find an extreme
environment?
The Good Earth/Chapter 16: Earth's Climate System
Extreme Climate Environments
Extreme environments:
• Reduced biodiversity
• Low population densities
• Fall within the dry and polar
climate regions
• Greenland and Antarctica
represent the world's
largest accumulations of
ice and snow
Antarctic landscape. Climbers on
their way to Mount Vinson, the
highest peak on the continent.
• Glacier = A long-lived mass
of slow moving snow and
ice on land
Continental glaciers/ice sheets – form at
polar latitudes. Alpine glaciers – found at
high elevations in mountainous regions.
The Good Earth/Chapter 16: Earth's Climate System
Extreme Climate Environments
Glaciers move and can tell us something about climate
change:
• Alpine glaciers are more susceptible to climate changes
• Individual alpine glaciers may last for decades or up to
thousands of years
The Good Earth/Chapter 16: Earth's Climate System
Extreme Climate Environments
The weight of thick
glacial ice causes it to
move.
In general they move
downslope.
Alpine glaciers move ~550 m/yr.
Ice sheets can move
hundreds of meters per
yr.
As the ice moves it transports pieces of bedrock
that fall off surrounding cliffs or are torn off by the
glacier.
Crevasses = steep,
narrow cracks in the
surface ice form as the
glacier changes shape.
Snow falling on the glacier is compacted into ice
crystals that contain trapped air bubbles.
The Good Earth/Chapter 16: Earth's Climate System
Extreme Climate Environments
Glaciers are composed of layers of ice
Snowflakes fall in accumulation zone and are
compacted into ice crystals
Air bubbles are trapped as the ice crystals are
buried lower in the glacier
The tiny air bubbles preserve a record
atmospheric composition at the time of their
formation
The layers in a glacier represent annual
accumulations of snow
Scientists can count the annual snow layers to
get an estimate of the glacier's age
Can combine age information and atmospheric
composition information from the air bubbles
and see a record of past climate
The Good Earth/Chapter 16: Earth's Climate System
Extreme Climate Environments
Zones of an alpine glacier
Zones are based on elevation
Accumulation zone – higher elevation,
thickest part of the glacier, addition of
snow exceeds loss by melting
Ablation zone – lower, thinner zone where
seasonal snow melts causing thaw of
underlying glacial ice
Snowline – boundary between
accumulation and ablation zones
The mass balance of the glacier is the
difference between how much ice and
snow accumulates vs. melts each year.
The Good Earth/Chapter 16: Earth's Climate System
Earth's Climate System Checkpoint 16.9
While hiking in the Sierra Nevada
Mountains of California you come across a
high valley filled with several meters of
snow and ice. What would you look for to
determine if it is just a big pile of snow and
ice or a glacier?
The Good Earth/Chapter 16: Earth's Climate System
Extreme Climate Environments
If ablation exceeds accumulation, a glacier melts faster than new ice
can be added and the front of the glacier retreats upslope.
• Scientists studying North Cascade glaciers have recorded a steady
decline in volume over the last two decades.
• Glaciers are about 1/3 smaller today than they were in the mid-1980's.
• Glaciers undercut adjacent mountainsides and scrape underlying
material causing erosion and mass wasting.
• Bits of rock frozen into base of glacier act like sand paper scouring the
underlying landscape.
• At the terminus (end) of the glacier, unsorted debris from clay size to
house size boulders collects. (Till = unsorted deposits)
• Ridges of till that surround the edge of the glacier = moraines
•
•
Terminal moraine – marks farthest limit of the glacier
Geologists can map rate of melting by looking at the location of the
terminal moraine and the terminus of the glacier.
The Good Earth/Chapter 16: Earth's Climate System
Extreme Climate Environments
Till
Tillite
Glacier terminus and moraine.
The edge of the moraine
represents deposits formed
when the terminus of the
glacier remained in one
location.
The Good Earth/Chapter 16: Earth's Climate System
Extreme Climate Environments
The presence of moraines in regions without present-day glaciers is
evidence for more extensive glaciers in the geologic past.
Moraines are seen in the Midwest and Great Plains states
Icebergs
breaking off
a glacier in
Greenland
Recession of the Gangotri glacier, India.
Larsen Ice shelf, Antarctica – terminus floating in
shallow water adjacent to a landmass
The Good Earth/Chapter 16: Earth's Climate System
Earth's Climate System Checkpoint 16.10
Examine the
two pictures
of the
glaciers at
left:
a. In the photos, identify as many features as you can.
b. In the photo on the right, what do you infer is the
origin of the dark stripes?
The Good Earth/Chapter 16: Earth's Climate System
Extreme Climate Environments
Glaciers that reach the ocean may
break off into icebergs or form an ice
shelf.
Icebergs and ice shelves carry clay,
sand, and boulders that were eroded
by the glacier.
As the ice melts into the ocean, these
materials are dropped and descend to
the ocean floor forming a dropstone
deposit.
The Good Earth/Chapter 16: Earth's Climate System
Earth's Climate System Checkpoint 16.11
Draw a diagram that illustrates the fate of a
snowflake that falls in the accumulation
zone of a growing alpine glacier. Begin
and end the path of the snowflake in the
atmosphere.
The Good Earth/Chapter 16: Earth's Climate System
Extreme Climate Environments
In most hot deserts, temperatures are high, annual
rainfall is less than 10 inches, and evaporation exceeds
precipitation.
Desert surfaces are a combination of sand, desert pavement, and rock
outcrops.
The Good Earth/Chapter 16: Earth's Climate System
Extreme Climate Environments
Many deserts are located around 30°N and S latitude – subtropical
deserts
Some are located in continental interiors far from moisture sources –
continental deserts
Some are located along a coast where cold ocean waters cool the air
and it loses its moisture before reaching land – coastal deserts
Some are located in polar regions and are dry, with relatively little ice
or snow – polar deserts
Some are found on the downwind side of a mountain range where the
rainshadow effect has depleted air of its moisture before it descends
down the landward side – rainshadow deserts
Deserts don't have to be hot, but always have less than 10 inches
of annual precipitation. Deserts are always dry.
The Good Earth/Chapter 16: Earth's Climate System
Earth's Climate System Checkpoint
16.13
The area around the South Pole receives
just a few centimeters of snowfall each
year. Is the South Pole a desert? Give
reasons to support your answer.
The Good Earth/Chapter 16: Earth's Climate System
Extreme Climate Environments
Erosion and Deposition in Deserts:
Occasional flash floods and wind action are responsible for eroding,
transporting, and depositing material in deserts.
Winds move
sediments by
suspension (fine
particles), saltation
(sand grains), and
creep (larger
particles). Can form
ripples in sand, and
desert pavement
where sand is
removed and
pebbles are left
behind.
The Good Earth/Chapter 16: Earth's Climate System
Extreme Climate Environments
Sand grains may be deposited together to form sand dunes.
The most common sand dunes have a gentle
windward face and a steep lee face. The dune
migrates slowly with the wind as sand is moved
from the gentle face to the steep face.
The Good Earth/Chapter 16: Earth's Climate System
Extreme Climate Environments
Cross beds = a pattern of sloping layers that slope in the
same direction the wind blows.
Cross beds can tell us the direction of prevailing winds
when the dunes were formed.
The Good Earth/Chapter 16: Earth's Climate System
Earth's Climate System Checkpoint 16.15
Complete the Venn diagram provided by placing the six listed
descriptions in the appropriate locations on the diagram. Add at
least an additional 4 characteristics.
1. Transport sediment in direction of
movement
Wind Action
Glacial Processes
2. Can transport large boulders
3. Form dunes
4. Occur most frequently at high
latitudes
5. Few associated plants and animals
6. Occur on at least 5 continents
7.
8.
9.
10.
The Good Earth/Chapter 16: Earth's Climate System
Go back to the Table of Contents
Go to the next section: Records of Climate
Change
The Good Earth/Chapter 16: Earth's Climate System
Records of Climate Change
Imagine you have boarded an airplane with no windows
and have flown somewhere far away. The pilot does not
tell you where you have landed. What evidence would you
use to determine the climate of the region?
Indicators of climate = proxies
Proxy = something that stands for something else
Example: the change in native woodlands in Missouri to
grasslands in Kansas is a proxy for the westward decrease
in precipitation.
Proxies of climate fluctuations include tree rings, oxygen
isotopes, and microfossils
The Good Earth/Chapter 16: Earth's Climate System
Records of Climate Change
Detailed, accurate data on
temperature and precipitation have
only been collected for about 150
years.
a) Average global temperatures
taken from land and ship-based
instruments since the late 1850's.
b) Average of temperatures from
the troposphere taken by satellites
since 1979. Two data
interpretations – UAH (Univ of
Alabama, Huntsville) and RSS
(Remote Sensing Systems) using
same data set.
What trend do you see on
both graphs? Is it real?
The Good Earth/Chapter 16: Earth's Climate System
Records of Climate Change
Changes in climate
patterns influenced
where past civilizations
were able to flourish
• Viking migration to
Greenland during warmer
temperatures – increased
length of Greenland
growing season
• When it cooled again
Vikings agricultural base
declined and environment
became more hostile
The Good Earth/Chapter 16: Earth's Climate System
Records of Climate Change
Climate change is
recorded in
archaeological
data, historical
records, and even
works of art.
Paintings from the
period 1550 – 1849
show more dark
skies and clouds.
Pieter Bruegel's
Winter Landscape
with Bird Trap
shows a time when
European rivers
were likely to freeze
over, a rare event
today.
The Good Earth/Chapter 16: Earth's Climate System
Records of Climate Change
Cultural records indicate three distinct climate periods for the Northern
Hemisphere in the last 1,000 years or so:
1. Medieval warm period - Temperatures were relatively warm from 1000 –
1450 A.D.
2. The Little Ice Age – A time of very cold temperatures but not really an ice
age. Occurred for about 400 years after the medieval warm period.
3. By the end of the 19th century climate moderated leading to our present
relatively warm temperatures, which exceed any in the last 1,000 years.
The Good Earth/Chapter 16: Earth's Climate System
Records of Climate Change
Annual climate records can be found in tree rings, lake sediments, and ice
layers.
Each year includes
earlywood (light) and
latewood (dark) growth.
Wide rings occur during wet,
warm years and narrow rings
during cold, dry years.
Usually it is necessary to
match partial records from
multiple trees to get a climate
record.
Short-term climate change is
recorded in tree rings
(hundreds of years).
The Good Earth/Chapter 16: Earth's Climate System
Records of Climate Change
Northern Wyoming precipitation record from tree ring analysis.
Precipitation records from 1895 onward were matched with tree ring
widths to estimate precipitation values for pre-1895 tree rings.
The Good Earth/Chapter 16: Earth's Climate System
Records of Climate Change
Lake sediments are often deposited in paired annual layers
called varves.
Varves reflect seasonal changes in deposition in a lake.
Algae grows on surface from spring to late fall
Dies in fall and sinks to bottom making a dark layer of
sediment
Sediment near lake margins comes from streams and is
thicker during periods of higher precipitation
During colder parts of year much of central lake sediment is
wind blown dust and clay, producing lighter sediment layer
Can cover longer periods of time that tree rings, and hold more
proxy information such as pollen from land plants, sediment
from nearby land sources, chemical changes due to
weathering, organic remains, and ash layers that can be
radiometrically dated.
The Good Earth/Chapter 16: Earth's Climate System
Records of Climate Change
Reconstructed temperature
records for the Northern
Hemisphere.
a. Red line = actual instrument
recorded temperature. Blue line
is reconstructed from climate
proxy data. Yellow line is an
average.
b. Temperature and snowfall
record of central Greenland over
last 17,000 years.
What strikes you about the upper
graph?
Notice that recent temperatures
exceed anything from the last
1,000 years. Why?
The Good Earth/Chapter 16: Earth's Climate System
Records of Climate Change
The thickness of ice layers is related to temperature and directly tied
to precipitation.
Yearly layers can be observed, counted, and studied for climate
information.
Oxygen isotopes serve as a proxy for long-term climate change.
18O
is heavier
than 16O. 16O is
much more
abundant in the
ocean than 18O.
Changes in the
ratio of these
isotopes
indicate
changes in
climate.
The Good Earth/Chapter 16: Earth's Climate System
Records of Climate Change
Lighter 16O isotopes evaporate with seawater and are returned to the ocean
through precipitation and runoff. When it is colder 16O is incorporated into
continental ice sheets which causes the oceans to become enriched with
heavier 18O that has not evaporated and precipitated onto ice sheets.
The Good Earth/Chapter 16: Earth's Climate System
Records of Changing Climate
The oxygen isotope record
acts as a
paleothermometer for
ancient climates.
Oxygen isotope ratios of
ocean water are recorded
in the calcium carbonate
shells of microscopic
foraminifera.
The ratios in the shells can
tell us about temperature
and ice volume in the
oceans in the past.
Large drops in biodiversity
usually correspond with
sudden climate changes.
The Good Earth/Chapter 16: Earth's Climate System
Records of Changing Climate
Climate records indicate that the Northern Hemisphere experienced
glaciation (Ice Age) during the last 2 million years:
Lower sea level
Land bridge between Siberia and Alaska
More forests in North America
Western U.S. deserts were cooler
North America was
dominated by a 3kilometer thick (1.9
mile) continental
glacier centered over
Canada.
The Good Earth/Chapter 16: Earth’s Climate System
Records of Changing Climate
The last Ice Age is divided into cold glacial intervals and warmer
interglacials. Temperatures during the glacials were at least 9-18°F colder
than today. Based on the length of interglacials, we are about 10,000 years
away from entering another cold glacial interval. What trends do you notice
on the above graph?
The Good Earth/Chapter 16: Earth’s Climate System
Records of Changing Climate
Younger Dryas – short, cold
interval marked by the
appearance of pollen from
polar wildflower Dryas
octopetala.
At end of Younger Dryas,
entered the Holocene, our
current interglacial.
Climate can change very
quickly as evidenced by the
graph at left.
At end of Younger Dryas
average annual temperature
of much of Northern
Hemisphere increased by
12°F in less than a decade!
The Good Earth/Chapter 16: Earth’s Climate System
Records of Climate Change
Hypothesis – rapid warming at the end of an especially cold
interval cause catastrophic failure of Northern Hemisphere ice
sheet, putting surges of icebergs into the Atlantic.
Addition of so much fresh water slowed thermohaline
circulation (Gulf Stream), causing a plummet in temperatures
in Europe, Asia, and Africa.
Longest ice core from Antarctica only records back less than
one million years.
To model earlier climate we must look at fossil chemistry and
sedimentary rock characteristics.
These proxies give us a record back to about 66 million years
ago.
The Good Earth/Chapter 16: Earth’s Climate System
Records of Climate Change
Earth was 18-27°F
warmer 52 million
years ago –
Hothouse Earth!
Temperature
contrast between
the equator and the
poles was much
less.
No polar ice caps.
65 million years of climate change. Temperature is
only correlated with earliest and latest portions of
the curve. Temperatures were generally warmer
than today until the major ice sheet of Antarctica
formed ~34 Ma.
Alligator-like
reptiles on islands
of northern
Canada.
The Good Earth/Chapter 16: Earth’s Climate System
Records of Climate Change
Implications for our future:
Freshwater sources today are smaller continental glaciers
such as Greenland.
At current melting rates this couldn’t produce enough
freshwater to generate the dramatic alteration in salinity
needed to significantly impact thermohaline circulation.
An abrupt catastrophic climate change is not likely to happen,
but a constant refreshing of the North Atlantic by melting of
Greenland can slow down the ocean conveyor – still can
have consequences!
Do humans indeed affect climate?
The Good Earth/Chapter 16: Earth’s Climate System
Go back to the Table of Contents
Go to the next section: Natural Causes of
Climate Change
The Good Earth/Chapter 16: Earth’s Climate System
Natural Causes of Climate Change
Causes of long-term global climate
change must operate on a global scale
over very long time intervals.
Most likely causes:
• Changing locations of continents and oceans due to
plate tectonics
• Changes in the Earth’s orbit around the sun
• Variations in the composition of the atmosphere such
as concentrations of greenhouse gases
The Good Earth/Chapter 16: Earth’s Climate System
Natural Causes of Climate Change
The last three major ice
ages have occurred when
large landmasses were
located near one or both
poles.
Must be land near poles
to build up long-lived
continental ice sheets.
Having landmasses near
the poles isn’t enough by
itself to create climate
changes.
What else might be
important?
Distribution of continents and oceans
at the time of Pangaea.
The Good Earth/Chapter 16: Earth’s Climate System
Natural Causes of Climate Change
Recall that water carries a lot of heat around the globe.
Ocean circulation patterns can impact climate!
Examples:
Closing of the connection between North and South America ~3 million
years ago  strengthened gulf stream, warmer water to North Atlantic
region, greater evaporation and precipitation in the form of snow,
greater albedo and less melting of northern glaciers leading to long
term formation of ice caps.
Separation of South America and Australia from Antarctica ~34 million
years ago  triggered large-scale glaciation of Antarctica, opened up
circulation patterns in Southern Ocean, isolated southern continent
from moderating climate influences from lower latitudes.
Earth’s climate involves interaction between geosphere, hydrosphere,
atmosphere, and biosphere.
The Good Earth/Chapter 16: Earth’s Climate System
Natural Causes of Climate Change
Small changes in Earth’s orbit, on scales of tens of
thousands of years, influence climate changes.
Milankovitch Cycles – caused by the interaction of Earth with the
gravitational fields of other planets. There are three principal variations:
1. Eccentricity of Earth’s orbit = shape of Earth’s orbit around the sun
varies from more circular to more elliptical. Changes occur on a
100,000 year cycle.
Which orbital path
would cause the most
extreme variations
between summer and
winter months?
The Good Earth/Chapter 16: Earth’s Climate System
Natural Causes of Climate Change
2. Changes in the tilt of the Earth’s axis = Earth’s axis is currently tilted
23.5 degrees. Over 41,000 years the tilt can change from 22-25
degrees. This changes the angle at which solar radiation strikes the
Earth.
Would a higher angle
of tilt or a lower angle
of tilt foster growth of
ice at the poles?
The Good Earth/Chapter 16: Earth’s Climate System
Natural Causes of Climate Change
3. Precession = The wobbling of the Earth on its spin axis (like a top).
Changes the direction of the axial tilt. It takes 23,000 years for the axis
to make a complete round trip back to where it started.
Today Earth’s axis is tilted toward the sun
during summer months. In 11,500 years it will
be the exact opposite. What will this mean for
our seasons?
The Good Earth/Chapter 16: Earth’s Climate System
Earth’s Climate System Checkpoint 16.21
What combination of changes in the Milankovitch
cycles would cause the highest and lowest
summer temperatures in North America?
The Good Earth/Chapter 16: Earth’s Climate System
Earth’s Climate System Checkpoint 16.22
Would the amount of incoming solar radiation
increase or decrease at the Arctic Circle during
July in the Northern Hemisphere if
1. Earth’s axis were vertical rather than tilted?
2. Earth’s orbit brought it closer to the sun?
3. The tilt of Earth’s axis were opposite to its
present orientation? (away from the sun)
The Good Earth/Chapter 16: Earth’s Climate System
Earth’s Climate System Checkpoint 16.23
Concisely describe five features that could cause
the temperature of a region of the Earth’s
surface to decrease.
The Good Earth/Chapter 16: Earth’s Climate System
Earth’s Climate System Checkpoint 16.23
From the information in this chapter, discuss what
you think would be some potential climate
scenarios for North America over the next 1,000
years.
The Good Earth/Chapter 16: Earth’s Climate System
The End
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The Good Earth/Chapter 16: Earth’s Climate System