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`
Wh t k
What
key ffeatures
t
d
determine
t
i th
the earths
th weather?
th ?
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What key features determine the earths climate?
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How does climate affect the location of the major biomes?
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Desert Biomes
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Grassland Biomes
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Forest Biomes
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Mountain Biomes
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Weather is an areas short-term
short term atmospheric conditions,
typically describe in terms of
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Temperature
Pressure
Moisture
Precipitation
Sunshine
Wind direction and speed
Two key
yp
principles
p
affect the weather
◦ Air Masses
◦ Pressure Changes
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o
o
o
o
Most of the dramatic changes
g in weather occur along
g a front,, the boundary
y
between two air masses with different temperatures and densities.
A warm front is the boundary between an advancing warm air mass, and the
cool one it is replacing.
Warm air is less dense
than cool air, and rises.
As warm front rises the
moisture begins
condensing into droplets
Gradually
y the clouds
thicken , descend to a
lower altitude, and
release their moisture.
A moist warm front brings
days of cloudy skies and drizzle
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o
o
o
o
A cold front is the leading
g edge
g of an advancing
g mass of cold air.
The cool air is more dense than the warm air, so stays close to the ground,
and wedges underneath the less dense warm air.
The rapidly
p y rising
g warm air
produces towering clouds
called thunderheads.
As the cold front passes
p
through we experience
high surface winds and
thunderstorms.
After the cold front passes
we usually have cooler
temperatures and clear
skies
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Weather is also affected by changes in atmospheric pressure.
pressure
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Atmospheric pressure is greater near the earth’s surface because the
molecules
l
l are squeezed
d ttogether
th under
d th
the weight
i ht off the
th air.
i
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An air mass with high pressure, called a high, contains cool, dense
air,
i thi
this descends
d
d ttowards
d th
the surface
f
and
db
becomes warmer. F
Fair
i
weather follows.
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A low
l
air
i pressure mass, called
ll d a llow, contains
i warm, llow d
density
i
air. This warm air rises, cools and condenses into clouds.
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Tornadoes and cyclones are two
examples of weather extremes.
Tornadoes are swirling funnel shaped
clouds that form over land.
land The US and
Australia or most prone to tornadoes.
Tornadoes occur when a large, dry cold
front runs into a large mass of humid
air.
As the large warm air mass moves
rapidly over the more dense mass of
cool air it rises rapidly and forms
t
ti
t th
k
strong
convection
currents
thatt suck
air upwards.
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Tropical
op ca cyclones
cyc o es a
are
e large,
a ge, da
dangerous
ge ous sto
storms
s tthat
at form
o
o
over
e
warm tropical seas.
They form when a cold air mass is
located above an organized cluster
of tropical thunderstorms.
Convection occurs which leads to
strong updrafts that lift the air and
moisture upwards.
The air cools as it rises and
condenses.
d
As the
h air expands
d it is
forced to diverge.
The removal of air at the upper
levels reduces pressure at the
surface, increasing convection.
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Tropical cyclones can kill and injure people, and damage
property and agricultural production. However they
sometimes have long-term ecological benefits.
I 1990 H
In
Hurricane
i
B
Brett
tt struck
t
k th
the G
Gulf
lf off M
Mexico.
i
IIn T
Texas,
costal bays and marches had become closed off from
freshwater inflows. The hurricane calved fresh channels
allowing
ll
ffresh
h water to flush
fl h out dead
d d vegetation and
d
excessive algae.
This
s lead
ead to tthe
eg
growth
o t o
of sea g
grasses
asses p
providing
o d g a su
suitable
tab e
habitat for shrimps, crabs, fish and ducks, providing and
ecological and economic benefit to the city.
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Climate is a regions long
long-term
term atmospheric
conditions.
The
e ttwo
o main
a factors
acto s dete
determining
g a region’s
eg o s
climate are
◦ Average temperature
◦ Average precipitation
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The temperature and precipitation patterns that
lead to different climates are caused primarily by
◦ The amount of incoming solar energy
◦ Air circulation patterns
p
◦ Water circulation patterns
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Uneven heating of the earths surface
◦ Air is heated much more at the equator where the sun’s
rays hit directly.
◦ At the poles, the rays must travel further, and heat a
greater area.
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Seasonal Changes
◦ The earths axis is tilted at 23.5 degrees, as a result
different regions are tipped towards, or away from the sun.
◦ This creates opposite seasons in northern and southern
hemispheres
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Rotation of the earth on its axis
◦ As the earth rotates, the surface moves faster under the air
masses at the equator and slower at the poles.
◦ This causes the major prevailing winds.
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Mountains affect local and regional climates
climates.
◦ Prevailing winds pick up moisture from an ocean
◦ On the windward side of a mountain range, air rises, cools
and releases moisture.
◦ On the leeward side of the mountain range, air descends
warms and releases little water.
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Wind is a vital p
part of our p
planets climate.
Wind also transports nutrients from one place to another.
Dust rich in phosphates and iron blows across the Atlantic
from the Sahara Desert. This helps
p to build up
p agricultural
g
soils in the Bahamas and supplies nutrients for plants in
the canopy of rain forests in Brazil.
Wind also transports harmful viruses, bacteria, fungi and
particles
i l off long-lived
l
li d pesticides.
i id
Particles of reddish-brown soil and pesticides banned in
the US are blown from Africa’s desert into skies over
Florida This makes it very difficult to meet air pollution
Florida.
standards during summer months.
Some types of fungi in the dust are also playing a role in
destroying corral reefs in Florida
Florida.
Pollution from rapidly industrialising China and central
Asia blow across the Pacific Ocean and degrade air quality
over the western US.
US
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Different climates lead to different communities of
organisms, especially vegetation.
The world can be divided into different biomes
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Deserts have little precipitation and little vegetation.
Deserts cover about 30% of the earths land surface.
They are found inland away from moist
coastal airs, or on the downside of
mountains in rain shadows.
Temperatures tend to vary greatly
between day and night due to a lack of
vegetation or moisture to hold the heat.
They can be found in tropical, temperate and polar regions.
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Plants:
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No leaves to reduce water loss
Open pores to take up CO2 only at night
Either deep roots to find ground water
Or network of shallow roots to absorb maximum surface water
Animals
◦ Animal tend to be small
◦ Hide by day or become dormant during long periods of heat
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Natural Capital Degradation
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Large desert cities
Soil destruction by off road vehicles
Depletion of underground water supplies
Land disturbance and pollution from mineral extraction
Deserts take a long time to recover from disturbances due to slow
plant growth and slow nutrient cycle, it can take decades to recover
from human activities
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Grasslands have enough precipitation to support
grasses, but insufficient to support large strands of
trees.
There are three main
kinds of grassland
◦ Tropical
◦ Temperate
◦ Polar
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Al called
Also
ll d savannas, these
th
grasslands
l d have
h
high
hi h
temperatures year round.
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They have two prolonged dry seasons and abundant
precipitation in the remaining two.
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They contain a large amount grazing and browsing hoofed
animals that feed on a variety
y of savanna p
plants.
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Humans have attempted to raise cattle on tropical grasslands,
this often helps in the destruction of grasslands into desert
through overgrazing, and increased reliance on water.
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Temperate Grasslands cover vast expanses of plains and rolling
hills in North and South America, Europe and Asia.
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In these grasslands
grasslands, winters are very cold
cold, summers are hot and
annual precipitation is fairly sparse and falls unevenly through
the year.
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Over-ground plants die each year and decompose producing
deep, fertile soil. This is held in place by the vast network of
roots from draught-tolerant grasses.
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Many of the world temperate grassland have been destroyed
through overgrazing, and ploughing of the land for crop growth.
This breaks up the soil roots and leave it vulnerable to erosion.
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During
g most of the year
y
polar
p
g
grasslands are bitterly
y cold,, swept
p
by frigid winds, and covered by ice and snow.
Winters are long and dark, and the rare precipitation falls mostly
as snow.
Th biome
The
bi
is
i carpeted
t d with
ith a thi
thick,
k spongy matt off llow-growing
i
plants, primarily grasses and mosses.
Trees or tall plants can not survive in the cold windy conditions.
Most annual growth takes place during the 6-8
6 8 week summer
summer.
The constant frozen groundwater leads to bogs and ponds in
summer, under which mosquitoes and flies thrive. These feed
g colonies of migrating
g
g birds.
large
Animals consist of hares, voles and ground squirrels which
burrow underground to escape the cold, and predators such as
the lynx, snow owl and arctic fox.
B
th cold,
ld d
iti
iis slow.
l
Th
f
h
Because off the
decomposition
Therefore
human
activities such as oil drilling, mines and military bases leave scars
that persist for centuries.
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Forests have enough precipitation to support
stands of trees and are found in tropical,
temperate and polar regions
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Tropical
p
rain forests are found near the equator
q
They have heavy rainfall for the majority of the year, meaning a
high humidity.
They have a warm average temperature which varies little by day
or by
b year.
Tropical rainforests are dominated by broadleaf evergreen
plants.
Typically the tall trees have shallow roots
roots, and wide bases.
bases The
top of the trees for a dense canopy blocking most light from
reaching the ground.
Tropical
p
rainforests are teeming
g with life and have incredible
biological diversity.
Much of the animal life, particularly bats and birds live in the
sunny canopy layer.
Alth
h these
th
f
t cover just
j t 2% off the
th earth’s
th’ land
l d surface
f
Although
forests
they are habitats for half of the earth’s terrestrial species.
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Temperate forests grow in areas with moderate
average temperatures that change significantly with
the season.
They have long warm winters
winters, cold but not severe
winters, and abundant precipitation spread evenly
throughout the year.
Trees typically include oak,
oak hickory
hickory, maple
maple, poplar
and beech. They survive cold winters by dropping
their leaves.
Penetration of more sunlight means a greater
diversity of plant life at ground level.
The most common animal species include deer, and
small mammals such as squirrels
squirrels, rabbits
rabbits, raccoons
and mice.
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Th
These
forests
f
t exist
i t in
i cold
ld climates
li t and
d consist
i t mostly
tl off
cone-bearing evergreen trees.
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They keep their narrow pointed leaves (needles) all year long.
This adaptation allows them to take advantage of the brief
summers without having to take time to grow new leaves.
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Beneath the trees p
plant diversity
y is low because few species
p
can survive the winters when soil moisture is frozen.
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wolves
Boreal forests contain a variety of wildlife
wildlife, such as wolves,
moose, martens and hares.
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Mountains make up almost a quarter of the worlds land
surface.
Dramatic changes in altitude, climate and soil take place over
a very short
h t distance.
di t
Because of steep slopes mountains soils are particularly
vulnerable to erosion, especially after the removal of trees or
vegetation.
They contain the majority of the worlds forests.
They play an important role in the hydrological cycle by
gradually releasing melting snow and ice.
Mountains are particularly vulnerable to human activities such
as timber extraction, mineral resources extraction,
hydroelectric dams and reservoirs, tourism through hiking
and skiing,
g, and soil damage
g from off road vehicles.