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Chapter 4: Ecosystems &
Communities
Starting with … Climate (4.1)
THINK ABOUT IT
 When you think about climate, you might
think of dramatic headlines: “Hurricane
Katrina floods New Orleans!” or “Drought
parches the Southeast!”
 But big storms and seasonal droughts are
better described as weather rather than
climate.
 What is climate, and how does it differ
from weather? How do climate and
weather affect organisms and
ecosystems?
Weather and Climate
 Weather: day-to-day condition of Earth’s atmosphere
 Climate: average conditions over long periods

defined by year-after-year patterns of temperature
and precipitation
 Climate is rarely uniform even within a region

Environmental conditions can vary over small
distances: microclimates
 Ex: Northern Hemisphere, south-facing sides of
trees and buildings receive more sunlight, often
warmer and drier, than north-facing sides
 These differences can be very important to many
organisms.
What factors determine
Global Climate?
 3 main influences
1.
2.
3.
Greenhouse Effect & Solar Energy
Solar Energy & Latitude
Heat transport
1-Solar Energy & the Greenhouse Effect
 Solar Energy


main force that shapes our climate
arrives as sunlight that strikes Earth’s surface
1-Solar Energy & the Greenhouse Effect
 Where does the energy go from there?:


reflected back into space
absorbed and converted into heat…
 Heat also radiates back into space
 trapped in the biosphere.
 Earth’s avg temp
= Heat that stays – Heat that is lost
1-Solar Energy & the Greenhouse Effect
 Earth’s temperature is controlled by concentrations of 3
greenhouse gases



carbon dioxide
methane
water vapor
 Function like glass in a greenhouse, allowing visible light to
enter but trapping heat

the greenhouse effect
1-Solar Energy & the Greenhouse Effect
 GH gas conc.
 GH gas conc.
 trap more heat Earth warms
 more heat escapes Earth cools
 Without greenhouse effect  Earth would be about 30°C
cooler than it is today
Animation
 http://www.youtube.com/watch?v=DuiQvPLWziQ
2-Latitude & Solar Energy
Uneven heating of Earth’s surface causes predictable variation in climate.
Why?
North Pole
Equator
Earth
South Pole
Radiation is more intense near the equator compared to the
poles
-it’s warmer near the equator than at the poles
2-Latitude & Solar Energy
Uneven heating of Earth’s surface causes atmospheric circulation
Greater heating at equator than poles
1. sun’s rays hit more directly
2. less atmosphere to penetrate
Therefore
1. Net gain of energy at equator
2. Net loss of energy at poles
2-Latitude & Solar Energy
 What about seasons? Why do we have them?
 Earth’s distance from the sun varies throughout the year –
doesn’t that cause the seasons?
 Tilt!
 Tilt of Earth’s axis  the amount of radiation received by
Northern and Southern Hemispheres to vary seasonally
 Northern Hem. has summer when it tilts toward the sun,
winter when it tilts away
 Southern Hem. has summer when it tilts toward the sun,
winter when it tilts away
2-Latitude & Solar Energy
When the north pole tilts toward the
sun, it gets more radiation – more warmth
during the summer
When the north pole tilts toward the
sun, the south pole tilts away
So when it’s summer in the north,
it’s winter in the south
SUMMER (Northern Hemisphere)
WINTER (Southern Hemisphere)
2-Latitude & Solar Energy
When the north pole tilts away
from the sun, it gets less radiation –
So it’s colder during the winter
When the north pole tilts away from the
sun, the south pole tilts toward it…
When it’s winter in the north,
it’s summer in the south
WINTER (Northern Hemisphere)
SUMMER (Southern Hemisphere)
3-Heat Transport in the Biosphere
 Unequal distribution of
heat across the globe
creates wind and ocean
currents
 transport heat and
moisture
 Earth has winds because
warm air is less dense
and rises, and cool air is
more dense and sinks
Air cools as it
rises, moisture
condenses and
falls as rain
Intense radiation at the
equator warms the air
Warm air rises,
collecting moisture
Lots of rain in the tropics!
Rising air is now dry…
some of the rising
air flows north
some of the rising
air flows south
Dry air descends
at around 30º N
Deserts
…and at around
30º S
The descending air flows N and S
Deserts
Arizona’s July temperature
Climate of any region is
predictable from
topography, wind and
ocean currents
>32ºC
29-32 ºC
27-29 ºC
24-27 ºC
21-24 ºC
18-21 ºC
16-18 ºC
13-16 ºC
Lesson Overview
Climate
3-Heat Transport in the Biosphere
Air that is heated by warm
areas of Earth’s surface—
such as near the equator—
rises, expands, and spreads
north and south, losing heat
along the way.
As the warm air cools, it sinks.
Lesson Overview
Climate
3-Heat Transport in the Biosphere
In cooler regions, near the
poles, chilled air sinks toward
Earth’s surface, pushing air at
the surface outward.
This air warms as it travels
over the surface and rises.
Lesson Overview
Climate
3-Heat Transport in the Biosphere
These upward and downward
movements of air create winds.
Winds transport heat from regions
of rising warmer air to regions of
sinking cooler air.
Earth’s rotation causes winds to
blow generally from west to east
over the temperate zones and from
east to west over the tropics and
the poles.
Lesson Overview
Climate
3-Heat Transport in the Biosphere
Similar patterns of heating and cooling occur in the oceans.
Surface water is pushed by winds.
Ocean currents, like air currents, transport enormous amounts of
heat.
Lesson Overview
Climate
Heat Transport in the Biosphere
Warm surface currents add moisture and heat to air that passes
over them.
Cool surface currents cool air that passes over them.
In this way, surface currents affect the weather and climate of
nearby landmasses.
Lesson Overview
Climate
Heat Transport in the Biosphere
Deep ocean currents are caused by cold water near the poles sinking
and flowing along the ocean floor.
This water rises in warmer regions through a process called
upwelling.
Ocean currents move 40% of “excess heat” from equator to poles
Driven by circulation of deep ocean waters
Deepwater formation occurs near Greenland and in Antarctic
60% of heat transport is carried by
atmosphere through storms that
move along pressure gradients
Earth’s climate is now warmer than at any time in the last 1000 years
1. increased solar input (small warming effect)
2. Increased sulfate aerosols reflects radiation (small cooling effect)
3. Increased greenhouse gas concentrations (large warming effect)
4. Land-cover change creates a darker surface (large warming effect)
Changes in solar orbit causes long-term variations in solar input to Earth
Shape of orbit
Wobble of tilt
Angle of tilt
Most major greenhouse gases are increasing
in atmospheric concentrations
Climate is warming most rapidly at high latitudes
This warming is most pronounced in Siberia and western North America
Functioning of ecosystems varies predictably with climate
Climate gives rise to predictable types of ecosystems
Distribution of ecosystems is predictable from global
patterns of wind and ocean circulation