Topography
and vegetation
influence
climate
by helping determine how the Sun’s energy is used on Earth. The abundance of plants and the type of land cover (such as soil, sand, or asphalt) impacts evaporation and ambient
temperature
.
The
biosphere
, the sum total of living things on Earth, profoundly
influences
climate
. Through photosynthesis, plants help regulate the flow of greenhouse gases in the
atmosphere
. Forests and oceans serve as “carbon sinks” that have a cooling impact on
climate
. Living organisms alter the landscape, through both natural growth and created structures such as burrows, dams, and mounds. These altered
landscapes
can
influence
weather
patterns
such as wind, erosion, and even
temperature
.
Climate Features
The most familiar features of a
region
’s
climate
are probably average
temperature
and precipitation. Changes in day-to-day, day-to-night, and seasonal
variations
also help determine specific
climates
. For example, San Francisco, California, and Beijing, China, have similar yearly
temperatures
and
precipitation
. However, the daily and
seasonal
changes make San Francisco and Beijing very different. San Francisco’s winters are not much cooler than its summers, while Beijing is hot in summer and cold in winter. San Francisco’s summers are dry and its winters are wet. Wet and dry seasons are reversed in Beijing—it has rainy summers and
dry
winters.
Climate
features also include
windiness
, humidity, cloud cover, atmospheric pressure, and fogginess. Latitude plays a huge factor in determining
climate
.
Landscape
can also help define
regional
climate
. A
region
’s elevation, proximity to the ocean or freshwater, and land-use patterns can all impact
climate
.
All
climates
are the product of many factors, including
latitude
,
elevation
,
topography
, distance from the ocean, and location on a continent. The rainy, tropical climate of West Africa, for example, is
influenced
by the
region
’s location near the Equator (
latitude
) and its position on the western side of the
continent
. The area receives direct sunlight year-round, and sits at an area called the intertropical convergence zone (ITCZ, pronounced “itch”), where moist trade winds meet. As a result, the
region
’s
climate
is warm and rainy.
Microclimates
Of course, no
climate
is uniform. Small
variations
, called
micro
climates
, exist in every
climate
region
.
Micro
climates
are largely
influenced
by topographic features such as lakes,
vegetation
, and cities. In large urban areas, for example, streets and buildings absorb heat from the Sun, raising the average
temperature
of the city higher than average
temperatures
of more open areas nearby. This is known as the “urban heat island effect.”
Large bodies of water, such as the Great Lakes in the United States and Canada, can also have
micro
climates
. Cities on the southern side of Lake Ontario, for example, are cloudier and receive much more snow than cities on the northern shore. This “lake effect” is a result of cold
winds
blowing across warmer lake water.
Climate Classification
In 1948, American climatologist Charles Thornthwaite developed a
climate
classification system that scientists still use today. Thornthwaite’s system relies on a
region
’s water budget and potential evapotranspiration.
Potential evapotranspiration describes the amount of water evaporated from a vegetated piece of land. Indices such as
humidity
and
precipitation
help determine a
region
’s moisture index. The lower its
moisture index
value, the more arid a
region
’s
climate
.
The major classifications in Thornthwaite’s
climate
classification are microthermal, mesothermal, and megathermal.
Microthermal
climates
are characterized by cold winters and low
potential
evapotranspiration
. Most geographers apply the term exclusively to the northern
latitudes
of North America, Europe, and Asia. A
microthermal
climate
may include the temperate
climate
of Boston, Massachusetts; the coniferous forests of southern Scandinavia; and the boreal
ecosystem
of northern Siberia.
Mesothermal
regions
have moderate
climates
. They are not cold enough to sustain a layer of winter snow, but are also not remain warm enough to support flowering plants (and, thus,
evapotranspiration
) all year.
Mesothermal
climates
include the Mediterranean Basin, most of coastal Australia, and the Pampas
region
of South America.
Megathermal
climates
are hot and humid. These
regions
have a high
moisture index
and support rich
vegetation
all year.
Megathermal
climates
include the Amazon
Basin
; many islands in Southeast Asia, such as New Guinea and the Philippines; and the Congo
Basin
in Africa.
Köppen Classification System
Although many
climatologists
think the Thornthwaite system is an efficient, rigorous way of classifying
climate
, it is complex and mapping it is difficult. The system is rarely used outside scientific publishing.
The most popular system of
classifying
climates
was proposed in 1900 by Russian-German scientist Wladimir Köppen. Köppen observed that the type of
vegetation
in a
region
depended largely on
climate
. Studying
vegetation
,
temperature
, and
precipitation
data, he and other scientists developed a system for naming
climate
regions
.
According to the Köppen
climate
classification system, there are five climate groups: tropical,
dry
, mild,
continental
, and polar. These
climate
groups
are further divided into climate types. The following list shows the
climate
groups
and their types:
Tropical
Tropical Climates
There are three climate types in the tropical group: tropical wet; tropical monsoon; and tropical wet and dry.
Tropical Wet: Rainforests
Places with a
tropical wet
climate
are also known as
rain
forests
. These
equatorial
regions
have the most predictable
weather
on Earth, with warm
temperatures
and regular rainfall. Annual rainfall exceeds 150 centimeters (59 inches), and the
temperature
varies more during a day than it does over a year. The coolest
temperatures
, about 20° to 23° Celsius (68°-73° Fahrenheit), occurs just before dawn. Afternoon
temperatures
usually reach 30° to 33° Celsius (86°-91° Fahrenheit).
Rain
forests
experience very little
seasonal
change, meaning average monthly
temperatures
remain fairly constant throughout the year.
Tropical wet
climates
exist in a band extending about 10° of
latitude
on either side of the
Equator
. This part of the globe is always under the
influence
of the intertropical convergence zone. The ITCZ follows a pendulum-like path during the course of a year, moving back and forth across the
Equator
with the seasons. It moves north during summer in the Northern Hemisphere, and south during the northern winter.
Some
tropical wet
climates
are wet throughout the year. Others experience more rainfall during the summer or winter, but they never have especially
dry
seasons
. The U.S. state of Hawaii; Kuala Lumpur, Malaysia; and Belém, Brazil, are examples of areas with
tropical wet
climates
.
Tropical Monsoon
Tropical monsoon climates are most found in southern Asia and West Africa. A
monsoon
is a
wind
system that reverses its direction every six months.
Monsoons
usually flow from sea to land in the summer, and from land to sea in the winter.
Summer
monsoons
bring large amounts of rainfall to tropical
monsoon
regions
. People living in these
regions
depend on the
seasonal
rains to bring water to their crops. India and Bangladesh are famous for their
monsoon
climate
patterns.
Tropical Wet and Dry: Savanna
Tropical wet and dry climates are sometimes called “
savanna
”
climates
after the grassland
ecosystem
defined by wet and
dry
periods.
Tropical wet and
dry
climates
sit just outside the ITCZ, near the
Equator
. They have three seasons. One season is cool and
dry
—when the warm, moist ITCZ is in the opposite hemisphere. Another season is hot and
dry
as the ITCZ approaches. The last season is hot and wet as the ITCZ arrives and the
region
experiences months as a
tropical wet
climate
.
Life in these tropical wet and
dry
regions
depends on the wet season’s rains. During years when rains are light, people and animals suffer through drought. During especially rainy years,
regions
may experience flooding. Havana, Cuba; Kolkata, India; and Africa’s vast Serengeti Plain are in the wet and
dry
tropics
.
Dry Climates
Regions
lying within the
dry
climate
group
occur where
precipitation
is low. There are two
dry
climate
types
:
arid
and semi
arid
. Most arid climates receive 10 to 30 centimeters (four to 12 inches) of rain each year, and semiarid climates receive enough to support extensive
grasslands
.
Temperatures
in both
arid
and
semi
arid
climates
show large daily and
seasonal
variations
. The hottest spots in the world are in
arid
climates
. The
temperature
in the
arid
Death Valley National Park, California, U.S., reached 56.7° Celsius (134° Fahrenheit) on July 10, 1913—the highest
temperature
ever recorded.
Although rainfall is limited in all
dry
climates
, there are a few parts of the world where it never rains. One of the driest places on Earth is the Atacama Desert of Chile, on the west coast of South America. Stretches of the Atacama may have never received rain in recorded history.
Semi
arid
regions
, such as the Australian outback, usually receive between 25 and 50 centimeters (10-20 inches) of rainfall every year. They are often located between
arid
and
tropical
climate
regions
.
Arid
and
semi
arid
climates
can occur where the movement of warm, moist air is blocked by mountains. Denver, Colorado, just east of the U.S. section of the Rocky Mountains, has this type of
dry
climate
, known as a “rain shadow.”
Mild Climates
Regions
with mild and continental climates are also called
temperate
regions
. Both
climate
types
have distinct cold seasons. In these parts of the world,
climate
is
influenced
mostly by
latitude
and a
region
’s position on the
continent
.
Mediterranean
Mediterranean climates have warm summers and short, mild, rainy winters.
Mediterranean
climates
are found on the west coasts of
continents
between 30° and 40°
latitude
, and along the shores of the Mediterranean Sea.
Mediterranean summers feature clear skies, cool nights, and little rain.
Humid Subtropical
Humid subtropical climates are usually found on the eastern sides of
continents
. In cities such as
Savannah
, Georgia, in the U.S.; Shanghai, China; and Sydney, Australia, summers are hot and humid. Winter can be severely cold.
Precipitation
is spread evenly through the year and totals 76 to 165 centimeters (30-65 inches). Hurricanes and other violent storms are common in these
regions
.
Marine West Coast
Weather
on both sides of a
continent
generally becomes cooler as
latitude
increases.
The marine west coast climate, a type of
mild
climate
typical of cities such as Seattle, Washington, in the U.S. and Wellington, New Zealand, has a longer, cooler winter than the
Mediterranean
climate
. Drizzle falls about two-thirds of winter days, and
temperatures
average about 5° Celsius (41° Fahrenheit).
Continental Climates
Areas with
continental
climates
have colder winters, longer-lasting snow, and shorter growing seasons. They are the transition zones between mild and
polar
climates
.
Continental
climates
experience extreme
seasonal
changes.
The range of
weather
in
continental
climate
regions
makes them among the most spectacular sites for
weather
phenomena. In autumn, for instance, vast
forests
put on their annual show of brilliant color before shedding their leaves as winter approaches. Thunderstorms and tornadoes, among the most powerful forces in nature, form mostly in
continental
climates
.
There are three types of
continental
climate
—warm summer, cool summer, and sub
arctic
. All these
climates
exist only in the Northern Hemisphere. Usually,
continental
climates
are found in the interior of
continents
.
Warm Summer
Warm summer climate
regions
often have wet summer seasons, similar to
monsoon
climates
. For this reason, this
climate
type
is also called humid continental. Most of Eastern Europe, including Romania and Georgia, has
warm summer
climates
.
Cool Summer
Cool summer climates have winters with low
temperatures
and snow. Cold
winds
, sweeping in from the
Arctic
, dominate winter
weather
.
People living in these
climates
have grown accustomed to the harsh
weather
, but those unprepared for such cold may suffer. Many of French Emperor Na
poleon
Bonaparte’s soldiers, for example, were used to the mild
Mediterranean
climates
of France. Thou
sands
died in bitter cold as they retreated from Russia’s
cool summer
climate
in the winter of 1812.
Subarctic
North of
regions
with
cool summer
climates
are
regions
with subarctic climates. These
regions
, including northern
Scandinavia
and
Siberia
, experience very long, cold winters with little
precipitation
.
Sub
arctic
climates
are also called boreal climates or taiga.
Polar Climates
The two polar climate types, tundra and ice cap, lie within the Arctic and Antarctic Circles near the North and South Poles.
Tundra
In tundra climates, summers are short, but plants and animals are plentiful.
Temperatures
can average as high as 10° Celsius (50° Fahrenheit) in July. Wildflowers dot the
landscape
, and flocks of migratory birds feed on insects and fish. Whales feed on microscopic creatures in the
region
’s cold, nutrient-rich waters. People have adapted to life on the tundra for thou
sands
of years.
Ice Cap
Few organisms survive in the ice cap climates of the
Arctic
and Ant
arctic
.
Temperatures
rarely rise above freezing, even in summer. The ever-present ice helps keep the
weather
cold by reflecting most of the Sun’s energy back into the
atmosphere
. Skies are mostly clear and
precipitation
is low. In fact, Ant
arctica
, covered by an ice cap 1.6-kilometers (one-mile) thick, is one of the largest, driest
deserts
on Earth.
High Elevation Climates
Many
geographers
and
climatologists
have modified the Köppen classification system over the years, including
geographer
Glen Trewartha, who added a category for high-elevation climates.
There are two high
elevation
climate
types
: upland and highland. Both highland and upland climates are marked by very different
temperatures
and levels of
precipitation
. Climbing a lofty mountain or reaching a plateau can be like moving toward the
poles
. On some mountains, such as Mount Kilimanjaro, Tanzania, the
climate
is tropical at the base and
polar
at the summit. Often,
high-
elevation
climate
differs from one side of the mountain to the other.
Influence of Climate
The
enormous
variety of life on Earth is largely due to the variety of
climates
that exist and the climate changes that have occurred in the past.
Climate
has
influenced
the development of cultures and civilizations. People everywhere have
adapted
in various ways to the
climates
in which they live.
Clothing
Clothing, for example, is
influenced
by
climate
. Indigenous
Arctic
cultures
of Europe, Asia, and North America, for example, developed warm, durable, fur and animal-skin clothing. This clothing was necessary for survival in the icy
climate
near the North
Pole
. Many parkas worn by
Arctic
peoples are not only insulated, but waterproof. This combats both the frigid
temperatures
and
precipitation
found in
polar
climates
.
Lightweight, papery tapa cloth, on the other hand, is part of many
cultures
in the warm, humid
climates
of Polynesia, in the South Pacific.
Tapa cloth
was traditionally made from dried leaves, coconut fibers, and breadfruit bark.
Tapa cloth
is delicate and loses strength when wet, which would be deadly near the
poles
but only inconvenient near the
Equator
.
Shelter
Climate
also
influences
how
civilizations
construct housing. For instance, the ancient Anasazi people of southern North America built apartments into tall cliffs. The sheltered, shady area kept residents cool in the hot,
dry
desert
climate
.
The yurt is a part of the identity of many
cultures
across the
windy
, semi
arid
steppe of Central Asia.
Yurts
are a type of original “mobile home,” a portable, circular dwelling made of a lattice of flexible
poles
and covered in felt or other fabric.
Yurts
protect residents from fierce
winds
, and their portability makes them an ideal structure for nomadic and seminomadic herding
cultures
on the
grassland
.
Agriculture
The development of
agri
culture
was very dependent on
climate
.
Ancient
agricultural
civilizations
, such as those in Mesopotamia and India, flourished where the
climate
was mild. Communities could grow
crops
every season, and experiment with different types of
crops
, livestock, and farming techniques.
The mild,
Mediterranean
climate
in which the Roman Empire developed, for instance, allowed farmers to cultivate
crops
, such as wheat, olives, grapes, barley, and figs.
Livestock
included cattle, sheep, goats, pigs, and even honeybees.
Like the
ancient
Romans,
ancient
cultures
of the Amazon
Basin
in South America were also able to develop agricultural practices. The chief domesticated trees in the Amazon were mostly harvested for food and medicine: Brazil nuts, Inga ynga fruit (commonly known as “ice-cream beans”), Amazon tree grapes, abiu (another tropical fruit), and cacao fruits (whose seeds are known as cocoa beans).
Today, farmers are still in tune with the
climate
. They plant certain
crops
according to the expected amount of rainfall and the length of the
growing season
. When the
weather
does not follow the typical
climate
pattern, it can mean hard times for farmers and higher food costs for consumers.
Climate Change
Climate
does not change from day to day like
weather
, but it does change over time. The study of historic
climate
change
is called paleoclimatology.
Climate
changes
happen slowly over hundreds or even thou
sands
of years. For example, periodic glacial periods have covered large portions of Earth with ice caps. Some
paleoclimatology
evidence shows that the Sahara
Desert
was once covered by plants and lakes during a warm “wet age.”
Climate
change
can happen for many reasons. The movement of tectonic plates, volcanic activity, and the tilt of Earth’s axis all have effects on
climate
. For example, after the eruption of the island volcano of Krakatoa, Indonesia, in 1883, winters and even summers in Asia and Europe were colder and darker. Volcanic ash blocked the sun. Farmers had to adjust to shorter, weaker
growing seasons
.
Climates
around the world were changed for years.
The so-called “Little Ice Age” was a period of
climate
change
extending from the 12th through the 19th centuries. The
Little Ice Age
was not a true
glacial period
, but describes colder
climates
around the world. In Europe, canals in Great Britain and the Netherlands were often frozen solid, allowing for ice skating. In North America, European colonists reported especially harsh winters.
Global Warming
Since the Industrial Revolution of the 19th century, human activity has begun to impact
climate
. The current period of
climate
change
is sometimes called “
global warming
.”
Global warming
is often associated with a runaway “greenhouse effect.” The
greenhouse effect
describes the process of certain
gases
(including carbon dioxide (CO2), methane, nitrous oxide (N2O), fluorinated
gases
, and ozone) trapping solar radiation in a planet's lower
atmosphere
.
Greenhouse
gases
let the sun’s light shine onto Earth’s surface, but they trap the heat that reflects back up into the
atmosphere
. In this way, they act like the glass walls of a greenhouse.
The
greenhouse effect
is a natural phenomenon and keeps Earth warm enough to sustain life. However, human activities that include burning fossil fuels and cutting down
forests
release
greenhouse
gases
into the
atmosphere
at an unprecedented rate.
The current period of
climate
change
has been documented by rising
temperatures
, melting
glaciers
, and more intense
weather
phenomena
.
Our planet’s
temperature
has risen about 1.1° C (2° F) since the late 19th century. Sixteen of the last 17 warmest years on record have occurred in the 21st century. According to NASA, not only was 2016 the warmest year on record, but eight of the 12 months that make up the year were the warmest on record for those respective months.
The current period of
climate
change
is also associated with the massive
retreat
of
glaciers
,
ice sheets
, and sea ice. Warmer
temperatures
have reduced the number of
glaciers
of Montana’s
Glacier
National Park from 150 in 1850 to just 26 today. In 2017, one of the largest icebergs ever recorded entered the ocean as a huge chunk of the Larsen C ice shelf broke off the Ant
arctic
Peninsula. Warmer ocean
temperatures
and warmer
ambient
air
temperatures
likely contributed to the fracturing of the
ice shelf
and the massive Ant
arctic
ice sheet
associated with it. Finally, both the extent and thickness of
Arctic
sea ice has declined rapidly during the past several decades. The famed Northwest Passage, the treacherous route connecting the North Atlantic and North Pacific ocean basins, is now habitually free of ice and safe enough for cruise ships to navigate.
Melting
glaciers
and
ice sheets
, as well as expansion of seawater as it warms, have contributed to
unprecedented
sea level rise.
Sea level rises
at about 2.3 millimeters (0.2 inch) every year, contributing to up to 900% more frequent
flooding
in coastal areas.
Increasing
temperatures
can change the
climate
impacts and even the classification of a
region
. For instance, low-lying islands may be
flooded
as
seawater
rises. The populations of island nations, such as Maldives or Comoros, have been forced to contemplate becoming “climate refugees”—people forced to leave their homes and migrate to a different
region
.
Heat in the
atmosphere
may increase the interaction of diverse weather systems. Unusually
arid
climates
in a semi
arid
region
may prolong
droughts
, for instance. In
regions
with
mild
climates
, the increased atmospheric moisture associated with humid
climates
may increase the likelihood of
hurricanes
and typhoons.
Climate
change
is also impacting organisms and species range. Organisms that have
adapted
to one
climate
may have to
migrate
or
adapt
to warmer
temperatures
. Manatees, for instance, are marine mammals native to tropical waters. As
temperatures
increase, manatees have been migrating as far north as New York City, New York.
Polar
bear populations, on the other hand, are venturing farther south as
Arctic
sea ice becomes more scarce.
Climate
change
can be mitigated through reducing greenhouse-
gas
emissions. This can mean investing in new technologies, relying more on renewable energy sources, making older equipment more energy-
efficient
, or changing consumer behavior.
