Climatology notes _ Daniel too

1.0 Introduction

The term climatology is derived from the Greek words Klima and Logos. Klima
refers to the supposed slope of the earth surface from the sun and its influence
to the temperature distribution etc.

Climatology is the study of climate or it’s the science of the study of the
atmosphere that seeks to describe and explain the nature of climate, why they
differ from place to place and vary from time to time and also seeks to
examine how various of its elements relate or interact with other elements of
the natural environment to influence natural processes as well as human
activities.

Climatic elements

Introduction:

The atmosphere

This is the gaseous realm or layer that surrounds’ the planet earth. It is made
up of gases, aerosols (suspended solid particles in the air including sea salts
and dusts) and water in the form of vapor. It is extremely important since it
controls climate and locations of biomes (recognizable subdivisions of the
terrestrial ecosystems).It is one of the four spheres of the earth system; the
others are the lithosphere, the hydrosphere and the Biosphere. These spheres
are constantly interacting and exchanging matter and energy. The
atmosphere is held to the earth by gravitational pull. Thus, air thins out and
pressure decreases up the atmospheric column.

Major climatic elements include;

1. Temperature

The temperature of an area is

dependent upon latitude or the distribution of incoming
1
and outgoing radiation; the nature of the surface (landor water); the altitude
; and the prevailing
winds. Moisture, or the lack of moisture, modifies
temperature. The more moisture in a region, the smallerthe temperature ran
ge, and the drier the region, thegreater the temperature range. Mois
ture is alsoinfluenced by temperature. Warmer air can hold moremoistur
e than can cooler air, resulting in increasedevaporation and a higher
probability of clouds and precipitation.
Moisture, when coupled with condensation and evaporation, is an extremely
important climatic element. It ultimately determines the type of climate for a
specific region

2. Precipitation

Precipitation is defined as
water reaching Earth’s surface by falling either in a liquid or a solid state.
It can be snow, hail, sleet, drizzle, fog, mist and rain. The most significant
forms are rain and snow. Precipitation has a wide range of
variability over the Earth’s surface.

Types of Rainfall

 Convectional Rainfall

This is where a water surface is heated by the sun, e.g. the sea. The air above
the sea then becomes heated making the air less dense so it rises and cools.
As we know cooler air can not hold as much water vapour as warm air
therefore when the rising air becomes too cold to hold the moisture the
condensation occurs giving us clouds. Once there is too much water in the
cloud for the air to support gravity forces the water to be released in what we
know as rain.

 Frontal Rainfall

2
When two air masses met, one is warmer than the other the warmer air is
forced to rise over the colder air. As this warm air rises it cools and forms
clouds just like the air in convectional rainfall.

 Relief Rainfall

Wind bringing moist air from the seashore starts to rise up a hillside. As this
air rises the air passes its Dew Point, the point at which condensation occurs,
and the vapour forms clouds. The water vapour then falls as precipitation on
top of the hill or on the other side.

Evaporation

Is the process by which water is converted from its liquid form to its vapor
form and thus transferred from land and water masses to the atmosphere.
Evaporation from the oceans accounts for 80% of the water delivered as
precipitation, with the balance occurring on land, inland waters and plant
surfaces. the rate of evaporation depends upon:

 Wind speed: the higher the wind speed, the more evaporation

 Temperature: the higher the temperature, the more evaporation

 Humidity: the lower the humidity, the more evaporation

3. Wind

Wind is the climatic element that transports heatand moisture into a

region. The climate of an area isoften determined by the properties of te
mperature and moisture that are found upstream of that
region.Climatologists are mostly interested in wind withregard to its di
rection, speed, and gustiness. Wind istherefore usually discussed in
terms of prevailingdirection, average speeds, and maximum gusts.

3
2.0 Flow of Energy through the Atmosphere

The suns radiation is the main source of power for many of the earth’s
activities. The energy generated from the sun travels in the form of
electromagnetic radiation (including light, heat and other forms. About 99%
of the radiation that reaches the earth is in the range encompassing visible
light, near infrared and a little ultra violet radiation.

An electromagnetic energy streams away from the sun in all directions. It

becomes less concentrated with distance. Of energy that reaches the outer
atmosphere of the earth, 6% is back scattered by air , 20% is reflected by
clouds, 3% is absorbed by clouds, 16% is absorbed by molecules of ozone,
water vapour and other gases in the atmosphere, living less than half of the
solar flux to reach the surface of the earth (51%). This energy is then used in
a number of processes, including the heating of the ground surface.
The solar energy reaching the earth warms it, causing evaporation of water
and brings rain and it drives the wind. A highly variable fraction of the sunlight
that reaches the earth’s surface is reflected all the way back into space. Snow
or white sand reflects much more than does a black volcanic rock or
vegetation. Some of the energy reaching the earth is absorbed while some is
re-emitted as infra-red radiation. Re-emitted infrared radiation would also
travel back into space but it is prevented by carbon dioxide and other gases,
which absorb it leading to greenhouse effects.

Net radiation and Radiation Global distribution

Net radiation at surface measures the balance between incoming and outgoing
radiation. In places where energy is coming faster than it is going out, net
radiation will be a positive quantity, producing a surplus. In other places where
energy is going out faster than it is coming, net radiation will be a negative
quantity, yielding a radiation deficit.

The amount of energy delivered at a surface is a function of the latitude and

the angle of the suns rays. The most energy is delivered when the sun is

4
directly overhead. The basic air movements and ocean circulation are caused
by the difference in solar energy from place to place. The air movement and
ocean circulations help distribute heat over the globe.

On average, air tends to rise directly over the equator because it is heated
most and becomes relatively less dense. Air moves in from either side of the
equator to replace the rising air, leading to the northeast and southeast trade
winds. The air that rises over the equator falls again over 300 north and south
of the latitudes and thus coupled with air falling over the pole drives the
prevailing westerlies.

Wind blowing over the oceans at the equator cause surface currents that carry
warm water to the poles and hence help in distributing heat to the poles. This
meteorological distribution of heat helps moderate climates; it blends what
would otherwise be much more distinct zones having profound differences in
climate.

3.0 Climate

It is simply the average weather conditions of a given place over a longer

period and normally exceeding 35 years and above.

Factors responsible for the variation of climate

 Altitude
 Latitude
 Distance of a place/ Continentality from the nearest large body of water
 Prevailing wind systems
 Ocean currents i.e Warm currents wash the eastern side of the
continents hence causing rainfall formation while cold currents wash the
western side of the continents causing no rainfall e.g. warm currents
include the Agulhas, kuroshio, Brazil currents while the cold ones include
Benguela currents, Peru currents and California etc.

5
  Aspect (direction in which the slope is facing in terms of the solar
insolation

World climates and classification

The study of climate is important in that,

1. It provides the basis for understanding of the factors that affect the
distribution of life systems on the earth surface as well as other factors
that affect those life systems
2. Play important role in conditioning the environmental circumstances
that favour the existence or occurrences of processes, events and
activities in their varieties over the earth surface
3. Climate influences the development of the soils
4. Also influences availability of water and the distribution on the
atmosphere and earth surface
5. It also influences the temperature of a given area
6. Climatic conditions of a place also determines the type of the vegetation
7. Climate influences the land use activities that can be undertaken

Climatic studies should therefore involve both small and large-scale patterns
of climate and how climatic conditions influence both the natural and human
environmental conditions as well, as how human beings respond to such
conditions. Large scale pattern of climate involve generalization that obscure
small scale subsystem.

Classification of climate

Climate can be classified into;

a) Microclimates

6
Refers to local small-scale climatic systems which involve a small distance,
process, activities that occur within localized region e.g. land and sea breeze.
It ranges from 0-25km and its study is called microclimatology

b) Macroclimate

Refers to large-scale climatic events, processes that cover a large distance i.e.
from continent to another continent and its very systematic. They are normally
classified with involvement of generalization that involves ignoring specific
local conditions but only captures the common conditions.

Climate classification systems

We have different types of classification and it differ because of;

1. People have different objectives of classification

2. Depending on the end user e.g. planning purposes
3. Depends on the expectation of the people

There are three fundamental types of classifications used in climatology.

Empirical systems of classification that are based on observable features.

The Koppen system discussed below is an empirical system based on
observations of temperature and precipitation. These are two of the easiest
climate characteristics that can be measured.

Genetic classification systems are those based on the cause of the climate.
A genetic system relies on information about climate elements like solar
radiation, air masses, pressure systems, etc.

Applied classification systems are those created for, or as an outgrowth

of, a particular climate-associated problem. The Thornthwaite classification
system is one based on potential evapotranspiration and thus groups climates
based on water requirements.

7
Köppen climate classification system

The Köppen climate classification system one of the most widely used systems
for classifying climate because it is easy to understand and data requirements
are minimal. It is largely based on annual and monthly means of temperature
and precipitation.

The Köppen system uses a letter coding scheme to classify climate. The five
main groups of climates are designated by capital letters. These are:

A - Tropical climates (sometimes identified as "equatorial" climates)

B - Dry climates

C – Moist subtropical mid-latitude climate

D - Subarctic climates ("snow" or "boreal" climates) - Moist continental mid-

latitude climate

E - Polar climates

A - Tropical climates (sometimes identified as "equatorial" climates)

 Normally called the tropical moist climate

 Has a temperature higher than 180c monthly
 They extend northwards and southwards from the equator to about 15-
250
 Rainfall is bi-modal and monthly its greater than 1500mm

It has three major sub divisions

1. Wet tropical climate-Af- Equatorial climate

 Have precipitation throughout the year and monthly temperature
variations is less than 30c

8
  Temperature ranges from 22-320c

2. Tropical monsoon climate- Am

 Are areas that have rainfall equal or more than rainfall received in Af
 Different in that, rainfall is mainly distributed within 7-9 months of
the year after which the rest of the year is dry
 Rainfall is normally received when temperature is highest (hottest
months hence rain is called monsoon)

3. Tropical wet and dry climate-Aw

 Precipitation during wet season is less than 1000mm and occur

during summer season

B - Dry climates

 Has insufficient / devoid of rainfall for most of the year and if there
is rainfall, its sporadic
 Evapotranspiration is higher than the amount of precipitation
received
 These type of climate occur in the interior of the continents that
are located along the main latitude areas of the world which are
characterized by descending air e.g sahara

Two major types;

1) Bw -climate (Dry arid climate)

 Are true deserts hence do not support vegetation growth
 Covered by sandy soils
 Precipitation is less than 250mm per year and cover 12% of the earth
surface and can be categorized into 2;
 Bwh-Hot deserts and found within the tropics
 Bwk- Found in high latitudes and are cold deserts

2) Bs -climate (Semi Arid climate of the world)

9
  Covered by grassland (savanna climate)
 Rainfall amount is bwt 500-750mm per annum
 Cover 14% of the earth surface and can be categorized into
 Bsh-Semi arid climate found in the tropical area
 Bsk- Semi arid climate found in the mid latitude climate

C – Moist subtropical mid-latitude climate

 Are climates that experience warm and humid summers and relatively
mild winters
 Extends between 30-500 north and south of the equator
 Occurs in Eastern and western borders of most continents
 During winter, main weather features are mid latitude cyclones and
convective thunderstorm

Divided into 3;

 Cfa –Humid sub tropical climate

 Normally hot and moist with frequent thunderstorm
 Winters are mild in terms of temperature and precipitation occurs from
the mid latitude cyclones
 Cfb-Marine climates
 Associated with coastal environments hence called marine climate
 Found on the western of the continent and characterized by the humid
hot summer
 Heavy precipitation occurs during winter
 Cs- Mediterranean climate
 Associated with Mediterranean sea and other similar environments
such as carlifornia in USA
 Receives rainfall during winter while summers are dry and associated
with the sub-tropical high pressure zone-600 N &S
 Dry period may exist for a period of 5 months

10
D - Subarctic climates ("snow" or "boreal" climates) - Moist
continental mid-latitude climate

 Have cool summer and cold winters

 Located in the pole ward of the c- climate
 Average temperature of slightly more than 100c and lowest temperature
is -30c
 Winters are severe and experience intense snow falls, strong winds and
bitter cold brought by then arctic masses

Types include;

 Dw-Dry winters
 Ds-Dry summers
 Df- Areas that are wet/ moist all season

E - Polar climates

 Have very cold temperatures throughout the year

 Found in Northern areas of N.America, Europe, Asia etc

Can be divided into;

 ET- Polar tundra climate

 Soils are permanently frozen in this climate hence characterized by
permafrost
 Common vegetation is Lichen and Mosses etc.
 EF- Polar Ice-caps
 Climatic that is permanently covered by snow and ice
 Is associated with high altitudes of the world that exceeds 5000m
within the tropics, 3000m within the mid- latitude zones

11
Microclimate

A micro-climate is a local atmospheric zone where the climate differs from the
surrounding area. Microclimates exist, for example, near bodies of water,
which may cool the local atmosphere, or in heavily urban areas where brick,
concrete, and asphalt absorb the sun's energy, heat up, and reradiate that
heat to the ambient air.

It is also caused by slope or aspect of an area. South-facing slopes in the

Northern Hemisphere and north-facing slopes in the Southern Hemisphere are
exposed to more direct sunlight than opposite slopes and are therefore
warmer for longer.

A microclimate can offer an opportunity as a small growing region for crops

that cannot thrive in the broader area; this concept is often used in
permaculture practiced in northern temperate climates.

a) Urban climate

Urban climates are the result of the interaction of many natural and
anthropogenic factors such as

 Air pollution,
 Building materials,
 Emission of heat from human activities

Hence causing climatic differences between cities and non-urban areas.

Factors controlling/influencing urban climate

a) Emission of anthropogenic heat

This is heat released from combustion of fossil fuels, industrial production and
from vehicles. The amount of heat emitted depends upon the energy use by
individuals, the population density, the amount of industry and the city's
location.

12
 b) Land cover-

May be preserved in the form of lawns or parks, but usually occupies only a
small part of the city area. The city surface often, therefore, has a very
complex character consisting of a mosaic of different surface
materials. Each surface material has a different albedo (a measure of the
amount of solar radiation reflected back into space or absorbed by
the surface).

c) Pollutants
d) Topography
e) Water bodies
f) Size and structure of the city
g) Number of human inhabitants
h) Latitude

Effects of Urban areas on local climate

In urban areas, there is a modification of natural energy flow by buildings and

mainly results from temperature increment, which in turn affects the local
climate. Temperature in urban areas is affected by the following factors:

1. The way in which the walls and roofs of buildings and the concrete or
road stone of paved areas behaved like exposed rock materials in having
high conductivities, heat capacities and abilities to reflect heat as well
as high heat storage capacity than natural soils.
2. The input of artificial heat generated by machinery, vehicles heating and
cooling systems.
3. The additional surface area of buildings with large vertical faces which
creates exchanges of heat mass and momentum.
4. The way, in which the large extent of impervious of surfaces shed
rainwater rapidly, fundamentally altering the urban moisture and heat
budget by reducing evaporation and transpiration

13
 5. The ejection of pollutants and dusts into the urban atmosphere as a
result of human activity which modify long wave radiation processes.
Buildings and paved surfaces have albedos, or abilities to reflect solar
radiation, which differ from natural earth surface materials. This reflected heat
is what causes the change in the local climate in urban areas

The urban climate can be improved by planning the urban structure in such a
way as to decrease the negative impact of both anthropogenic and natural
factors. For example, through the strategic location of parks and water bodies
(e.g. ponds and lakes) and by building factories downwind of the city so
that air pollution is taken away by the wind and not brought into the urban
environment.

Urban heat island

As urban areas develop, changes occur in the landscape. Buildings, roads, and
other infrastructure replace open land and vegetation. Surfaces that were
once permeable and moist generally become impermeable and dry. This
development leads to the formation of urban heat islands—the phenomenon
whereby urban regions experience warmer temperatures than their rural
surroundings.

The annual mean air temperature of a city with one million or more people
can be 1 to 3°C warmer than its surroundings and on a clear, calm night, this
temperature difference can be as much as 12°C. Even smaller cities and
towns will produce heat islands, though the effect often decreases as city size
decreases.

Types of urban heat island

1. Surface urban heat island

Present at all times of the day and night and most intense during the day. Day
temperature is between 10 to 15°C while night temperature is between 5-
10°C.
14
 2. Atmospheric urban heat island

Divided into two;

 Canopy layer urban heat island; Exist in the layer of air where people
live, from the ground to below the tops of trees and roofs
 Boundary layer urban heat island; Starts from the rooftop and
treetop level and extend up to the point where urban landscapes no
longer influence the atmosphere. This region typically extends no more
than one mile (1.5 km) from the surface.

Canopy layer urban heat islands are the most commonly observed of the two
types and are often the ones referred to in discussions of atmospheric urban
heat islands. Atmospheric urban heat islands are often weak during the late
morning and throughout the day and become more pronounced after sunset
due to the slow release of heat from urban infrastructure. The timing of this
peak, however, depends on the properties of urban and rural surfaces, the
season, and prevailing weather conditions.

Atmospheric heat islands vary much less in intensity than surface heat islands.
On an annual mean basis, air temperatures in large cities might be 1 to 3°c
warmer than those of their rural surroundings.

Lines on a map connecting points of the same temperature (isotherms)

generally show a circular pattern with the temperature decreasing towards the
city suburbs.

Factors responsible for the development of atmospheric urban heat

Islands

1) Reduced vegetation in urban Areas

In rural areas, vegetation and open land typically dominate the landscape.
Trees and vegetation provide shade, which helps lower surface temperatures.
They also help reduce air temperatures through a process called

15
evapotranspiration, in which plants release water to the surrounding air, dis-
sipating ambient heat. In contrast, urban areas are characterized by dry,
impervious surfaces, such as conventional roofs, sidewalks, roads, and
parking lots. Built up areas evaporate less water, which contributes to
elevated temperatures.

2) Properties of urban materials

Properties of urban materials, in particular solar reflectance, thermal

emissivity, and heat capacity, also influence urban heat island development,
as they determine how the sun’s energy is reflected, emitted, and absorbed.
Built up communities generally reflect less and absorb more of the sun’s
energy. This absorbed heat increases surface temperatures and contributes to
the formation of atmospheric urban heat islands.

3) Urban geometry

Refers to the dimensions and spacing of buildings within a city. Urban

geometry influences wind flow, energy absorption, and a given surface’s
ability to emit long-wave radiation back to space. In developed areas, surfaces
and structures are often at least partially obstructed by objects, such as
neighboring buildings, and become large thermal masses that cannot release
their heat very readily because of these obstructions. Especially at night, the
air above urban centers is typically warmer than air over rural areas.

4) Anthropogenic heat

Refers to heat produced by human activities. It can come from a variety of

sources and is estimated by totaling all the energy used for heating and
cooling, running appliances, transportation, and industrial processes. Anthro-
pogenic heat varies by urban activity and infrastructure, with more energy-
intensive buildings and transportation producing more heat.

5) Other factors

16
  Weather; Two primary weather characteristics affect urban heat island
development: wind and cloud cover. In general, urban heat islands form
during periods of calm winds and clear skies, because these conditions
maximize the amount of solar energy reaching urban surfaces and
minimize the amount of heat that can be convected away. Conversely,
strong winds and cloud cover suppress urban heat islands.

 Geographic location; Climate and topography, which are in part deter-

mined by a city’s geographic location, influence urban heat island
formation. For example, large bodies of water moderate temperatures
and can generate winds that convect heat away from cities. Nearby
mountain ranges can either block wind from reaching a city, or create
wind patterns that pass through a city.

Negative effects of atmospheric urban heat islands

 Increased energy consumption;

Elevated temperatures in cities increase energy demand for cooling and add
pressure to the electricity grid during peak periods of demand, which generally
occur on hot afternoons, when offices and homes are running cooling systems,
lights, and appliances.

 Elevated emissions of air pollutants and greenhouse gases;

Higher temperatures can increases energy demand, which generally causes

higher levels of air pollution and greenhouse gas emissions.

 Compromised human health and comfort ;

Urban heat islands can also exacerbate the impact of heat waves, which are
periods of abnormally hot, and often humid, weather. Sensitive populations,
such as children, older adults, and those with existing health conditions, are
at particular risk from these events.

17
  Impaired water quality;

Surface urban heat islands degrade water quality, mainly by thermal pollution.
Pavement and rooftop surfaces that reach temperatures 27 to 50°C higher
than air temperatures transfer this excess heat to storm water.

Reducing atmospheric urban heat islands

 Planting trees and vegetation

 Increasing the number of parks and lakes in our cities.
 use of green roofs and cool roofs (Green building technology)

4.0 The concept of climate change

Climate change is the variations in the earth’s global climate system. It

describes the variability of the climate over scale ranging from decades to
million years.

Generally, climate change is caused by two factors,

a) Processes that are internal to the earth surface

b) Forces that are external to the earth surface (Climate forcing)s

Hence, climate change is due to;

1) Natural climate change

2) Anthropogenic climate change

The causes of natural climate change include volcanism, orbit variations, solar
output, plate tectonics, changes in the ocean current direction etc. while
anthropogenitic change is mainly caused by human beings. It is mainly due to
unsustainable human activities such as;

 Industrialization
 Deforestation
 Burning of fossil fuels
18
  Land use activities etc. slash and burn

All these activities cause global warming which is induced increase in

temperature on the earths atmosphere caused by green house gases leading
to the depletion of the ozone layer. Rapidly increasing of green house gases
threatens to trap the heat into the lower atmosphere and raise the global
temperature causing an enhanced green house effect

Main green house gases are carbon dioxide, nitrous oxide gas, methane gas,
water vapour, ozone gas and chlorofluorocarbons11&12 (CFC).

a) Carbon dioxide

It contributes about 49% of the global warming and has a lifespan of 500
years in the atmosphere. Produced as a result of industrialization,
deforestation and direct burning of fossil fuels.

b) Nitrous oxide (N2O)

Contributes to a bout 6% of global warming and mainly produced by biotic

processes of nitrification and denitrification including also the application and
use of fertilizers in agriculture.

c) Methane gas

Its sources of emission are agricultural activities (wetland farming and

irrigation), intensive cattle raising (Digestive systems of ruminant animals)
and fermentation of domestic wastes and biomass materials. Contributes to
18% of global warming and has a life span of 7-10 years in atmosphere.

d) Chlorofluorocarbons (CFCs)

These are gases commonly used in spray cans, foam blowing and
refrigeration. Their concentration in the atmosphere is low, they have a
lifetime of 65-110 years in the atmosphere, and they contribute to 15% of the
global warming.

19
The effects of the green house.

The effects of green house effect includes the temperature will rise more in
the poles than at the equator, Rainfall pattern will alter and length of the
seasons could change leading to differing patterns of agriculture, different
crops, different areas being suitable or unsuitable for intensive farming.
Higher temperature and more carbon dioxide could lead to higher rates of bio-
synthesis. Sea level changes i.e. 17-26cm by 2030 corresponding to the 1cm
to 20c warming over the same period due to the melting of the mountain
glaciers and the expansion of warming sea, also sea changes will lead to the
rapid loss of the land to the sea (pacific islands have disappeared due to the
melting of Northern hemisphere ice sheets (Lewis,1988a); Vulnerability of
coastal areas to flooding from storm surges i.e.( Bay of Bengal and
Bangladesh), increased intrusion of saltwater into surface and ground water
systems leading to loss of agricultural land.

Green house effect will change climate which will affect boundaries of
ecosystems and the mix of species that compose them. These will have
implications for human activities that depend on natural ecosystem, Changes
in ecological patterns, Changes in the flora and fauna of the lake and river
system. In addition, the rate of extinction of species would increase
substantially if climate changes rapidly and outstrips the capacity of biomes
and ecosystem to adapt.

Loss of forests northern(coniferous boreal forests) because they will be

invaded by the broad leaved species from the south. Temperate forests would
be invaded by grassland and the desert. Warming and aridity together could
contribute to higher incidence of fires as well as to less congenial growing
conditions. Climate change (and sea level rise) would affect the process of
investment in water supplies, construction, Energy generation, water
availability and variability because quality would be affected by flow rates and
turbidity. Matter and Feddema, 1986; have suggested that green house effect
could have the effect of diminishing water supply overall.

20
Also there will be changes in the spatial extend and height distribution of
clouds, changes in water content, drop size distribution and the proportions
of liquid water and ice cloud present (Mitchell et al.1989).Green house effect
would lead to invasion by a number of species resulting in the alteration in
species composition of fish fauna (Mandrak,1989). On the other hand,
increase of carbon dioxide could cause increased production of c3 crops
(wheat, rice, cassava barley etc) due to increased photosynthesis.

Mitigation measures of green house effects

1. A forestation and re-a forestation so as to reduce the amount of green

house gases i.e. carbon dioxide concentration in the atmosphere.
2. Incase of methane emissions, the gas can be trapped in the landfills and
used as source of energy.
3. For carbon dioxide release reduction, the thermal efficiency of plants
used should be efficient, increasing the usage of non-carbon
dioxide emitting technologies.
4. Encouraging the use of nuclear power emission which reduces carbon
dioxide substantially. Others, the use of tidal power, wave power, wind
power, use of solar power etc.
5. Requirement of further research (The house of commons select
committee on energy, 1989)
6. Encouraging the use of fuel switching i.e. (The greater use of gas
combined cycle gas turbines) rather than the development of more
efficient coal or oil-fired systems.
7. (Siefritz, 1989), Global disruption of climate by green house effects may
be mitigated by placing mirrors in orbit to reflect some of the incoming
radiation.
8. Use of fusion energy and transmitting to the ground via electronic beam
(suggestion).
9. People should be educated on the effects of the green house and they
should be prepared to cope up with it such as flooding and shortage of
water etc.
21
 3.0 Climate change

Will global temperature change influence the frequency and intensity of the
EL Nino phenomena in the equatorial pacific? Recent years have shown how
this periodic build up of warm water in the eastern pacific can have widespread
repercussions, sometimes with catastrophic consequences from Indonesia to
California and Peru, East Africa and perhaps more extensively.

Global warming especially if it’s concentrated in the higher latitudes, may be

expected to cause the melting and breakup of ice sheets around the Antarctic.
The number of summer days in which melting occurs has been increasing at
the rate of about one extra day per year since 1970, and the consequential
ice-sheet collapse has been rapid as evidenced by satellite images. Ice sheet
melting will result in rise in sea level. Rising sea level will give rise to many
bio-geographical problems especially in low-lying islands and coastal regions
of the world such as flooding, destruction of habitats, killing of people and
displacement, intrusion of salty water into fresh water reservoirs,

One must also differentiate between shifts in biome boundaries as a result of

climate change and changes in the distributional patterns of species. The
tundra biome, for example, whether, in polar regions or alpine regions, is likely
to contract as climate warms.

According to 2001 IPCC Third Assessment Report, the poorest countries would
be hardest hit, with reductions in crop yields in most tropical and sub-tropical
regions due to decreased water availability, and new or changed insect pest
incidence. In Africa and Latin America, many rain fed crops are near their
maximum temperature tolerance, so that yields are likely to fall sharply for
even small climate changes; falls in agricultural productivity of up to 30% over
the 21st century are projected. Marine life and the fishing industry will also be
severely affected in some places.

22
Climate change induced by increasing greenhouse gases is likely to affect
crops differently from region to region. For example, average crop yield is
expected to drop down to 50% in Pakistan whereas corn production in Europe
is expected to grow up to 25% in optimum hydrologic conditions.

More favorable effects on yield tend to depend largely on realization of the

potentially beneficial effects of carbon dioxide on crop growth and increase of
efficiency in water use. Decrease in potential yields is likely to be caused by
shortening of the growing period and decrease in water availability.

Most agronomists believe that agricultural production will be mostly affected

by the severity and pace of climate change, not so much by gradual trends in
climate. If change is gradual, there may be enough time for biota adjustment.
Rapid climate change, however, could harm agriculture in many countries,
especially those that are already suffering from rather poor soil and climate
conditions, because there is less time for optimum natural selection and
adaptation.

Rising carbon dioxide levels would also have effects, both detrimental and
beneficial, on crop yields. The overall effect of climate change on agriculture
will depend on the balance of these effects. Assessment of the effects of global
climate changes on agriculture might help to properly anticipate and adapt
farming to maximize agricultural production

In the long run, the climatic change could affect agriculture in several ways:

 Productivity, in terms of quantity and quality of crops

 Agricultural practices, through changes of water use (irrigation) and

agricultural inputs such as herbicides, insecticides and fertilizers
 Environmental effects, in particular in relation of frequency and intensity
of soil drainage (leading to nitrogen leaching), soil erosion, reduction of
crop diversity

23
  Rural space, through the loss (Aridity and desertification) and gain of
cultivated lands, land speculation, land renunciation, and hydraulic
amenities.
 Adaptation, organisms may become more or less competitive, as well
as humans may develop urgency to develop more competitive
organisms, such as flood resistant or salt resistant varieties of rice.

Soil climate and its effects on crop production

Higher air temperatures will also be felt in the soil, where warmer conditions
are likely to speed the natural decomposition of organic matter and to increase
the rates of other soil processes that affect fertility. Additional application of
fertilizer may be needed to counteract these processes and to take advantage
of the potential for enhanced crop growth that can result from increased
atmospheric CO2. This can come at the cost of environmental risk, for
additional use of chemicals may impact water and air quality. The continual
cycling of plant nutrients--carbon, nitrogen, phosphorus, potassium, and
sulfur--in the soil-plant-atmosphere system is also likely to accelerate in
warmer conditions, enhancing CO2 and N2O greenhouse gas emissions.

Drier soil conditions will suppress both root growth and decomposition of
organic matter, and will increase vulnerability to wind erosion, especially if
winds intensify. An expected increase in convective rainfall--caused by
stronger gradients of temperature and pressure and more atmospheric
moisture--may result in heavier rainfall and where it does occur, such
"extreme precipitation events" can cause increased soil erosion. Also, it causes
reduced soil fertility, increased salinity and the costs of erosion control may
be more than offset the beneficial effects of a warmer climate, leading to
ultimately to reduced yields and higher production costs.

Increased wind erosion will enhance more loss of the water from the ground
surface thereby causing deficiency in the plants growth.

24
Other effects might include,

i. Reduced water availability to plants

ii. Changes in irrigation agriculture (Changes in management)-
The demand for water for irrigation is projected to rise in a warmer
climate, bringing increased competition between agriculture-already the
largest consumer of water resources in semi -arid regions and urban as
well as industrial users
iii. Climate variability
Extreme meteorological events, such as spells of high temperature,
heavy storms, or droughts, disrupt crop production.
iv. Changes in Fertilizer Use

More use of fertilizers may be needed to maintain soil fertility where increases
in leaching that stems from increased rainfall etc.

Urban Heat Islands, Climate Change, and Global Warming

Urban heat islands refer to the elevated temperatures in developed areas

compared to more rural surroundings. Urban heat islands are caused by
development and the changes in radiative and thermal properties of urban
infrastructure as well as the impacts buildings can have on the local
microclimate. For example, tall buildings can slow the rate at which cities cool
off at night. Heat islands are influenced by a city’s geographic location and by
local weather patterns, and their intensity changes on a daily and seasonal
basis.

The warming that results from urban heat islands over small areas such as
cities is an example of local climate change. Local climate changes resulting
from urban heat islands fundamentally differ from global climate changes in
that their effects are limited to the local scale and decrease with distance from
their source. Global climate changes, such as those caused by increases in the
25
sun’s intensity or greenhouse gas concentrations, are not locally or regionally
confined.

Climate change, refers to any significant change in measures of climate (such

as temperature, precipitation, or wind) lasting for an extended period
(decades or longer). Climate change may result from:

 Natural factors, such as changes in the sun’s intensity or slow changes

in the Earth’s orbit around the sun
 Natural processes within the climate sys tem (e.g. changes in ocean
circulation)
 Human activities that change the atmosphere’s composition (e.g.
burning fossil fuels) and the land surface (e.g. deforestation,
reforestation, or urbanization).

Global warming is an average increase in the temperature of the atmosphere

near the Earth’s surface and in the lowest layer of the atmosphere, which can
contribute to changes in global climate patterns. Global warming can occur
from a variety of causes, both natural and human induced.

The impacts from urban heat islands and global climate change (or global
warming) are often similar. For example, some communities may experience
longer growing seasons due to either or both phenomena. Urban heat islands
and global climate change can both also increase energy demand, particularly
summertime air conditioning demand, and associated air pollution and
greenhouse gas emissions.

3.4 Climate sensitivity

Climate sensitivity describes how sensitive the global climate is to a change in

the amount of energy reaching the Earth's surface and lower atmosphere. For
example, we know that if the amount of carbon dioxide (CO2) in the Earth's
atmosphere doubles this will cause an energy imbalance by trapping more
26
outgoing thermal radiation in the atmosphere, enough to directly warm the
surface approximately 1.2°C. However, this does not account for feedbacks,
for example ice melting and making the planet less reflective gas.
Climate sensitivity is the amount the planet will warm when accounting for the
various feedbacks affecting the global climate.

4.0 The water balance

Hydrological cycle

Figure 1: Schematic diagram of the hydrologic cycle

The water cycle, also known as the hydrological cycle, describes the
continuous movement of water on, above and below the surface of the Earth.
Although the balance of water on Earth remains constant over time, individual
water molecules can come and go, in and out of the atmosphere. The water
moves from one reservoir to another, such as from river to ocean, or from the

27
ocean to the atmosphere, by the physical processes of evaporation,
condensation, precipitation, infiltration, runoff, and subsurface flow. In so
doing, the water goes through different phases: liquid, solid (ice), and gas
(vapor).

The water cycle involves the exchange of heat, which leads to temperature
changes. For instance, when water evaporates, it takes up energy from its
surroundings and cools the environment. When it condenses, it releases
energy and warms the environment. These heat exchanges influence climate.
By transferring water from one reservoir to another, the water cycle purifies
water, replenishes the land with freshwater, and transports minerals to
different parts of the globe. It is also involved in reshaping the geological
features of the Earth, through such processes as erosion and sedimentation.
Finally, the water cycle figures significantly in the maintenance of life and
ecosystems on Earth.

Three parts of hydrological cycle include, evaporation, precipitation and

infiltration.

 Evaporation

Evaporation is when the sun heats up water in rivers or lakes or the ocean
and turns it into vapor or steam. The water vapor or steam leaves the river,
lake or ocean, plants and goes into the air.

The rate at which the water molecules diffuse into the atmosphere will depend
on factors such,

 The availability of moisture at the surface of the earth (humidity)

 Temperature
 Wind
 Hours of sunshine
 Water characteristics
 Condensation

28
Condensation is the formation of liquid drops of water from water vapor. It is
the process which creates clouds, and so is necessary for rain and snow
formation as well. Condensation in the atmosphere usually occurs as a parcel
of rising air expands and cools to the point where some of the water vapor
molecules clump together faster than they are torn apart from their thermal
energy. A very important part of this process is the release of the latent heat
of condensation. This is the heat that was absorbed when the water was
originally evaporated from the surface of the Earth, a process that keeps the
Earth's surface climate much cooler that it would otherwise be if there were
no water.

The heat removed from the surface through evaporation is thereby released
again higher up in the atmosphere when clouds form. Another way in which
condensation occurs is on hard surfaces, such as during the formation of dew.
Water condensing on a glass of ice water, or on the inside of windows during
winter, is the result of those glass surfaces' temperature cooling below the
dew point of the air which is in contact with them.

 Precipitation

Precipitation occurs when so much water has accumulated that the air cannot
hold it anymore. The clouds get heavy and water falls back to the earth in
the form of rain, hail, sleet, fog or snow

Internal transfer process (water balance)

Between the input and output, there is extensive movement of water, which
takes place in the atmosphere, land and ocean. This is known as the internal
transfer process. It acts to redistribute water so that the inputs and the output
are kept in balance. The major internal transfer of the hydrological cycle
includes,

 Interception
 Run off
 Infiltration and percolation
29
Significance of the hydrological cycle

1. It leads to the formation of clouds in the atmosphere

2. The cycle creates an ecological balance in the water supply between the
atmosphere and the ground

3. It leads to the formation of rainfall which assists in agricultural

production and vegetation growth

4. Leads to the distribution of water on the earths crust

5. It assists in the oxygen and carbon cycles in the atmosphere

6. It connects /links the atmosphere, hydrosphere and the lithosphere

THE EARTH ATMOSPHERE

Introduction
Welcome to topic four. The topic begins with the definition of the term
atmosphere. The topic also describes the stratification of the earth’s
atmosphere.

4.1 The Earth Atmosphere

The earth is made up of four spheres namely: Hydrosphere, Atmosphere,

Biosphere and lithosphere

Atmosphere is a blanket of transparent and odourless gases enveloping the

earth surface. Earth atmosphere has four primary layers, which are the
troposphere, stratosphere, mesosphere, and thermosphere.

4.2 Stratification of the Atmosphere

Principal layers
30
The Earth atmosphere has four primary layers, which are the troposphere,
stratosphere, mesosphere, and thermosphere. From highest to lowest, the
five main layers are:

 Exosphere: 700 to 10,000 km (440 to 6,200 miles)

 Thermosphere: 80 to 700 km (50 to 440 miles)
 Mesosphere: 50 to 80 km (31 to 50 miles)
 Stratosphere: 12 to 50 km (7 to 31 miles)
 Troposphere: 0 to 12 km (0 to 7 miles)

4.2.1 Exosphere

The exosphere is the outermost layer of Earth's atmosphere (i.e. the upper
limit of the atmosphere). It extends at an altitude of about 700 km above sea
level, to about 10,000 km. The exosphere merges with the emptiness of outer
space, where there is no atmosphere.

This layer is mainly composed of extremely low densities of hydrogen, helium

and several heavier molecules including nitrogen, oxygen and carbon dioxide.
The exosphere is located too far above Earth for any meteorological
phenomena to be possible.

The exosphere contains most of the satellites orbiting Earth.

4.2.2 Thermosphere

The thermosphere is the second-highest layer of Earth's atmosphere. It

extends from the mesopause (which separates it from the mesosphere) at an
altitude of about 80 km (up to the thermopause at an altitude range of 500–
1000 km. The height of the thermopause varies considerably due to changes
in solar activity. Because the thermopause lies at the lower boundary of the
exosphere, it is also referred to as the exobase. The lower part of the
thermosphere, from 80 to 550 kilometres above Earth's surface, contains the

31
4.2.3 Ionosphere.

This atmospheric layer undergoes a gradual increase in temperature with

height. Unlike the stratosphere, wherein a temperature inversion is due to the
absorption of radiation by ozone, the inversion in the thermosphere occurs
due to the extremely low density of its molecules. The temperature of this
layer can rise as high as 1500 °C (2700 °F). This layer is completely cloudless
and free of water vapor.

4.2.4 Mesosphere

The mesosphere is the third highest layer of Earth's atmosphere, occupying

the region above the stratosphere and below the thermosphere. It extends
from the stratopause at an altitude of about 50 km to the mesopause at 80–
85 km above sea level.

Temperatures drop with increasing altitude to the mesopause that marks the
top of this middle layer of the atmosphere. It is the coldest place on Earth and
has an average temperature around −95 °C. The wind speed is 3000km/h at
the mesosphere.

4.2.5 Stratosphere

The stratosphere is the second-lowest layer of Earth's atmosphere. It lies

above the troposphere and is separated from it by the tropopause. This layer
extends from the top of the troposphere at roughly 12 km above Earth's
surface to the stratopause at an altitude of about 50 to 55 km.

It contains the ozone layer, which is the part of Earth's atmosphere that
contains relatively high concentrations of that gas. The stratosphere defines a
layer in which temperatures rise with increasing altitude. This rise in
temperature is caused by the absorption of ultraviolet radiation (UV) radiation
from the Sun by the ozone layer, which restricts turbulence and mixing.

32
The stratospheric temperature profile creates very stable atmospheric
conditions, so the stratosphere lacks the weather-producing air turbulence
that is so prevalent in the troposphere. The stratosphere is almost completely
free of clouds and other forms of weather. This is the highest layer that can
be accessed by jet-powered aircraft.

4.2.6 Troposphere

The troposphere is the lowest layer of Earth's atmosphere. It extends from

Earth's surface to an average height of about 12 km, although this altitude
actually varies from about 9 km (30,000 ft) at the poles to 17 km (56,000 ft)
at the equator, with some variation due to weather. The troposphere is
bounded above by the tropopause, a boundary marked in most places by a
temperature inversion and in others by a zone which is isothermal with height.

The temperature usually declines with increasing altitude in the troposphere

because the troposphere is mostly heated through energy transfer from the
surface.

The troposphere contains roughly 80% of the mass of Earth's atmosphere.

The troposphere is denser than all its overlying atmospheric layers because a
larger atmospheric weight sits on top of the troposphere and causes it to be
most severely compressed. It is primarily composed of nitrogen (78%) and
oxygen (21%) with only small concentrations of other trace gases.

Solar radiation (or sunlight) is the main source of energy on Earth received
from the Sun. However its only 45% of the energy released that is received
on the earth. Much is lost through scattering, absorption and reflection.

Topic Summary
The topic has defined the earth’s atmosphere and discussed the various layers
in the atmosphere. The topic has also discussed the stratification of the earth’s

33
atmosphere and described the vertical distribution of temperature from the
surface of the earth to the limits of the atmosphere.

Glossary

Exosphere: is the outermost layer of Earth's atmosphere (upper limit of the

atmosphere)

Mesosphere: is the third highest layer of Earth's atmosphere, occupying the

region above the stratosphere and below the thermosphere

Stratosphere: is the second-lowest layer of Earth's atmosphere

Thermosphere: is the second-highest layer of Earth's atmosphere

Troposphere: is the lowest layer of Earth's atmosphere

34