Energy
- We know that energy can take on many forms.
- One important form of energy, relative to life on Earth, is kinetic energy.
- Simply defined, kinetic energy is the energy of motion.
- The amount of kinetic energy that a body possesses is dependent on the speed of its motion and its mass.
- At the atomic scale, the kinetic energy of atoms and molecules is sometimes referred to as heat energy.
Temperature
- Kinetic energy is also related to the concept of temperature.
- Temperature is defined as the measure of the average speed of atoms and molecules.
- The higher the temperature, the faster these particles of matter move.
- At a temperature of -273.15° Celsius (absolute zero) all atomic motion stops.
- Heat is often defined as energy in the process of being transferred from one object to another because of difference in temperature between them.
- Heat is commonly transferred around our planet by the processes of conduction, convection, advection, and radiation.
Other important definitions
Some other important definitions related to energy, temperature, and heat are:
- Heat Capacity - is the amount of heat energy absorbed by a substance associated to its corresponding temperature increase.
- Specific Heat - is equivalent to the heat capacity of a unit mass of a substance or the heat needed to raise the temperature of one gram (g) of a substance one degree Celsius. Water requires about 4 to 5 times more heat energy to raise its temperature when compared to an equal mass of most types of solid matter. This explains why water bodies heat more slowly than adjacent land surfaces.
- Sensible Heat - is heat that we can sense. A thermometer can be used to measure this form of heat. Several different scales of measurement exist for measuring sensible heat. The most common are: Celsius scale, Fahrenheit scale, and the Kelvin scale.
- Latent Heat - is the energy needed to change a substance to a higher state of matter. This same energy is released from the substance when the change of state (or phase) is reversed. The diagram below describes the various exchanges of heat involved with 1 gram of water.
The Earth's Atmosphere
The atmosphere is a thin layer of gas which surrounds the Earth. This picture shows the two most important layers known as the troposphere and the stratosphere. The air gets thinner and thinner the higher you go, 90% of all the molecules in the atmosphere are in the troposphere. Air is a mixture of various gases.
| The present composition of the atmosphere is: |
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Besides water vapour, several other gases are also present in much smaller amounts:
- Carbon monoxide (formula CO)
- Neon (Ne)
- Oxides of nitrogen
- Methane (CH4)
- Krypton (Kr)
Concentrations of these gases are measured in parts per million (ppm)
The atmosphere has changed a lot compared to the Earth's early atmosphere, but for the last billion years it has remained pretty constant. We now need to look at 3 atmospheric problems:
The Greenhouse effect
The earth is surrounded by a blanket of gases. This blanket traps energy in the atmosphere, much the same way as glass traps heat inside a greenhouse. This results in an build up of energy, and the overall warming of the atmosphere. The greenhouse effect is a natural process which made life on Earth possible. Without naturally occurring greenhouse gases such as water vapour, carbon dioxide, methane and nitrous oxide, the Earth's surface temperature would be 33°C cooler, a chilly -18°C rather than the tolerable 15°C.
When we talk about the greenhouse effect we mean the ENHANCED effect which is caused by the increase of greenhouse gases from human sources. Since the beginning of industrialization, 200 years ago, concentrations of these gases have increased . It is estimated that the Earth's average temperature has risen by 0.6°C since 1880 because of emissions of greenhouse gases from human activity.
The main sources of these emissions, particularly carbon dioxide, methane and nitrous oxide, are:
- the combustion of large amounts of fossil fuels (producing CO2)
- deforestation (less trees mean that less CO2 is being mopped up)
A increase in global temperatures may seem great, you might even think of 'Costa del Blackpool'. Unfortunately global warming will probably result in big swings in weather patterns across the world. Summers will become dryer and hotter, Winters will be wetter and colder. Other things will start to happen:
- Thermal expansion of the water and melting of continental glaciers would cause sea levels to rise, possibly as much as two feet, by the end of next century.
- Rising temperatures could lead to changes in regional wind systems which would influence global rainfall distribution and lead to the redistribution and frequency of floods, droughts and forest fires.
- Increased sea temperatures would cause the destruction of coral reefs around the world.
- Climate change would create favourable conditions for growth in insect populations. This would likely have a bad effect on agriculture and human health and result in a spread of malaria and other tropical diseases.
- Water supplies would become disrupted and droughts would be more common
There is a lot of controversy surrounding global warming, views range from those who believe that there is nothing to worry about to those who believe that the world is heading for a global catastrophe.
Damage to the ozone layer
Ozone is oxygen that contains molecules that have 3 oxygen atoms (O3). The molecule is triatomic instead of the usual O2 molecule which is diatomic. There is a layer of ozone high up in the atmosphere which shields the Earth from the sun's harmful UV rays, these rays can lead to an increase in skin cancer. The ozone is present in very small quantities but it is enough to absorb the UV rays preventing them reaching the surface.
Scientists began to investigate the ozone layer in the 1970's, it wasn't until the mid 1980's that alarm bells started to ring. Concentrations of ozone appeared to be dropping in certain areas of the world (the layer was starting to thin-out). The cause of this reduction was thought to be man-made. The images below highlight the Ozone depletion over the Southern Hemisphere 1980-1991:-
In 1985 over 60 countries pledged to phased out a group of chemicals called CFC's. These very stable chemicals were once widely used in aerosols and refrigerators. It was thought that their release into the atmosphere produced chlorine radicals which reacted with O3 to produce O2. The emission of CFC's into the environment is now greatly reduced, unfortunately the damage has already been done and the CFC molecules, thanks to their stability, are still causing ozone depletion.
Acid rain
Rain water is naturally acidic due to carbon dioxide which partially reacts with water to give carbonic acid (H2O + CO2 -> H2CO3). When we talk about acid rain we mean the ENHANCED effect which is caused by other gases released when fossil fuels are burnt. Two gases are the main culprits:
- Sulphur dioxide - Fossil fuels often contain a lot of sulphur impurities which burn to give sulphur dioxide. The SO2 reacts with water in the atmosphere to from a weak solution of sulphuric acid.
- Nitrogen oxides - Under normal conditions nitrogen and oxygen don't react together. At very high temperatures (in an engine) a small proportion of oxygen reacts with nitrogen to give nitrogen oxides. These oxides react with water in the atmosphere to from a weak solution of nitric acid acid.
The dilute acid falls to ground as acid rain which causes the following problems:
- Lakes become acidic and plants and fishes die as a result
- Tree growth is damaged, whole forests can die as a result
- Acid rain attacks metal structures and also buildings made of limestone
One method of reducing the amount of SO2 that gets pumped into the atmosphere is to remove the sulphur impurities from the fuel.
Climate Classification
The Köppen Climate Classification Systemis the most widely used system for classifying the world's climates. Its categories are based on the annual and monthly averages of temperature and precipitation. The Köppen system recognizes five major climatic types; each type is designated by a capital letter.
A - Tropical Moist Climates: all months have average temperatures above 18° Celsius.
B - Dry Climates: with deficient precipitation during most of the year.
C - Moist Mid-latitude Climates with Mild Winters.
D - Moist Mid-Latitude Climates with Cold Winters.
E - Polar Climates: with extremely cold winters and summers.
Tropical Moist Climates
Tropical moist climates extend northward and southward from the equator to about 15 to 25° of latitude. In these climates all months have average temperatures greater than 18° Celsius. Annual precipitation is greater than 1500 mm. Three minor Köppen climate types exist in the A group, and their designation is based on seasonal distribution of rainfall. Af or tropical wet is a tropical climate where precipitation occurs all year long. Monthly temperature variations in this climate are less than 3° Celsius. Because of intense surface heating and high humidity, cumulus and cumulonimbus clouds form early in the afternoons almost every day. Daily highs are about 32° Celsius, while night time temperatures average 22° Celsius. Am is a tropical monsoon climate. Annual rainfall is equal to or greater than Af, but most of the precipitation falls in the 7 to 9 hottest months. During the dry season very little rainfall occurs. The tropical wet and dry or savanna (Aw) has an extended dry season during winter. Precipitation during the wet season is usually less than 1000 millimeters, and only during the summer season.
Dry Climates
The most obvious climatic feature of this climate is that potential evaporation and transpiration exceed precipitation. These climates extend from 20 - 35° North and South of the equator and in large continental regions of the mid-latitudes often surrounded by mountains. Minor types of this climate include:
- BW - dry arid (desert) is a true desert climate. It covers 12% of the Earth's land surface and is dominated by xerophytic vegetation. The additional letters h and k are used generally to distinguish whether the dry arid climate is found in the subtropics or in the mid-latitudes, respectively.
- BS - dry semiarid (steppe). Is a grassland climate that covers 14% of the Earth's land surface. It receives more precipitation than the BW either from the intertropical convergence zone or from mid-latitude cyclones. Once again, the additional letters h and k are used generally to distinguish whether the dry semiarid climate is found in the subtropics or in the mid-latitudes, respectively.
Moist Subtropical Mid-Latitude Climates
This climate generally has warm and humid summers with mild winters. Its extent is from 30 to 50° of latitude mainly on the eastern and western borders of most continents. During the winter, the main weather feature is the mid-latitude cyclone. Convective thunderstorms dominate summer months. Three minor types exist: Cfa - humid subtropical; Cs - Mediterranean; and Cfb - marine. The humid subtropical climate (Cfa) has hot muggy summers and frequent thunderstorms. Winters are mild and precipitation during this season comes from mid-latitude cyclones. A good example of a Cfa climate is the southeastern USA.
Cfb marine climates are found on the western coasts of continents. They have a humid climate with short dry summer. Heavy precipitation occurs during the mild winters because of the continuous presence of mid-latitude cyclones. Mediterranean climates (Cs) receive rain primarily during winter season from the mid-latitude cyclone. Extreme summer aridity is caused by the sinking air of the subtropical highs and may exist for up to 5 months. Locations in North America are from Portland, Oregon to all of California.
Moist Continental Mid-latitude Climates
Moist continental mid-latitude climates have warm to cool summers and cold winters. The location of these climates is pole ward of the C climates. The average temperature of the warmest month is greater than 10° Celsius, while the coldest month is less than -3° Celsius. Winters are severe with snowstorms, strong winds, and bitter cold from Continental Polar or Arctic air masses. Like the C climates there are three minor types: Dw - dry winters; Ds - dry summers; and Df - wet all seasons.
Polar Climates
Polar climates have year-round cold temperatures with the warmest month less than 10° Celsius. Polar climates are found on the northern coastal areas of North America, Europe, Asia, and on the landmasses of Greenland and Antarctica. Two minor climate types exist. ET or polar tundra is a climate where the soil is permanently frozen to depths of hundreds of meters, a condition known as permafrost. Vegetation is dominated by mosses, lichens, dwarf trees and scattered woody shrubs. EF or polar ice caps has a surface that is permanently covered with snow and ice.
