Atmosphere

The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night.
Dry air contains roughly (by volume) 78% nitrogen, 21% oxygen, 0.93% argon, 0.038% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1%. The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space.

Structure of the atmosphere

Principal layers of the atmosphere
The atmosphere of the Earth may be divided into several distinct layers, as the following figure indicates.

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Troposphere

The troposphere is where all weather takes place. The air pressure at the top of the troposphere is only 10% of that at sea level (0.1 atmospheres).The troposphere begins at the surface and extends to between 7 km at the poles and 17 km at the equator, with some variation due to weather. The troposphere is mostly heated by transfer of energy from the surface, so on average the lowest part of the troposphere is warmest and temperature decreases with altitude. The troposphere contains roughly 80% of the mass of the atmosphere. The tropopause is the boundary between the troposphere and stratosphere.

Stratosphere

Above the troposphere is the stratosphere, where air flow is mostly horizontal. The stratosphere extends from the tropopause to about 51 km Temperature increases with height, which restricts turbulence and mixing. The stratopause, which is the boundary between the stratosphere and mesosphere, typically is at 50 to 55 km.

Mesosphere

The mesosphere extends from the stratopause to 80–85 km. It is the layer where most meteors burn up upon entering the atmosphere. Temperature decreases with height in the mesosphere. The mesopause, the temperature minimum that marks the top of the mesosphere, is the coldest place on Earth and has an average temperature around −100 °C (−148.0 °F; 173.1 K).

Thermosphere

Temperature increases with height in the thermosphere from the mesopause up to the thermopause, then is constant with height. The temperature of this layer can rise to 1,500 °C (2,730 °F). The International Space Station orbits in this layer, between 320 and 380 km (200 and 240 mi). The top of the thermosphere is the bottom of the exosphere, called the exobase.

Exosphere

The outermost layer of Earth's atmosphere extends from the exobase upward. Here the particles are so far apart that they can travel hundreds of km without colliding with one another. Since the particles rarely collide, the atmosphere no longer behaves like a fluid.. The exosphere is mainly composed of hydrogen and helium.

Other layers

Within the five principal layers determined by temperature are several layers determined by other properties. • The thin ozone layer is contained within the upper stratosphere has a high concentration of ozone, a particularly reactive form of oxygen. This layer is primarily responsible for absorbing the ultraviolet radiation from the Sun. In this layer ozone concentrations are about 2 to 8 parts per million, which is much higher than in the lower atmosphere but still very small compared to the main components of the atmosphere. The width of this layer is about 15–35 km (though the thickness varies seasonally and geographically). About 90% of the ozone in our atmosphere is contained in the stratosphere.

• Above the stratosphere is the mesosphere and above that is the ionosphere (or thermosphere), where many atoms are ionized (have gained or lost electrons so they have a net electrical charge). The ionosphere, the part of the atmosphere that is ionized by solar radiation, so they have a net electrical charge). It extends from 50 to 1,000 km and typically overlaps both the exosphere and the thermosphere. It forms the inner edge of the magnetosphere. The ionosphere is very thin, but it is where aurora take place, and is also responsible for absorbing the most energetic photons from the Sun, and for reflecting radio waves, thereby making long-distance radio communication possible. The Mesosphere and Ionosphere
Above the stratosphere is the mesosphere and above that is the ionosphere (or thermosphere), where many atoms are ionized (have gained or lost electrons so they have a net electrical charge). The ionosphere is very thin, but it is where aurora take place, and is also responsible for absorbing the most energetic photons from the Sun, and for reflecting radio waves, thereby making long-distance radio communication possible.
The structure of the ionosphere is strongly influenced by the charged particle wind from the Sun (solar wind), which is in turn governed by the level of Solar activity. One measure of the structure of the ionosphere is the free electron density, which is an indicator of the degree of ionization. Here are electron density contour maps of the ionosphere for months in 1957 to the present. Compare these simulations of the variation by month of the ionosphere for the year 1990 (a period of high solar activity with many sunspots) and 1996 (a period of low solar activity with few sunspots):

• The homosphere and heterosphere are defined by whether the atmospheric gases are well mixed. In the homosphere the chemical composition of the atmosphere does not depend on molecular weight because the gases are mixed by turbulence.The homosphere includes the troposphere, stratosphere, and mesosphere. Above this layer, at about 100 km the composition varies with altitude. The gases stratify by molecular weight, with the heavier ones such as oxygen and nitrogen present only near the bottom of the heterosphere. The upper part of the heterosphere is composed almost completely of hydrogen, the lightest element.

• The planetary boundary layer is the part of the troposphere that is nearest to the Earth's surface and is directly affected by it. During the day the planetary boundary layer usually is well-mixed, while at night it becomes stably stratified with weak or intermittent mixing. The depth of the planetary boundary layer ranges from as little as about 100 m on clear, calm nights to 3000 m or more during the afternoon in dry regions.

Climate and Weather

People often confuse climate and weather – the two really are quite different.
What is weather?
Weather describes the condition of the atmosphere over a short period of time e.g. from day to day or week to week, while climate describes average conditions over a longer period of time. Humidity, air temperature and pressure, wind speed and direction, cloud cover and type, and the amount and form of precipitation are all atmospheric characteristics of the momentary conditions we call weather.
The sun is ultimately responsible for the weather. Its rays are absorbed differently by land and water surfaces (equal amounts of solar radiation heat the ground more quickly than they do water). Differential warming, in turn, causes variations in the temperature and pressure of overlying air masses.
The weather we experience is influenced by many factors, including your location’s latitude, elevation, and proximity to water bodies. Even the degree of urban development, which creates “heat islands,” and the amount of snow cover, which chills an overlying air mass, play important roles.
Weather is defined as the state of the atmosphere at some place and time, usually expressed in terms of temperature, air pressure, humidity, wind speed and direction, precipitation, and cloudiness.
Meteorologists study weather.

What is Climate?
It has been said that “climate is what you expect; weather is what you get”. In other words, you can expect snow in Russia in January, but you may or may not get it on a particular day.
The climate of an area or country is known through the average weather over a long period of time. If an area has more dry days throughout the year than wet days, it would be described as a dry climate; a place which has more cold days than hot days would make it known to have a cold climate. Climate is defined in terms of the average (mean) of weather elements (such as temperature and precipitation) over a specified period of time (30 years according to the World Meteorological Organization).

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Effects of Climate Change

How will climate change effect us, there are many factors that will be affected by climate change including rising sea levels, drought and loss of agricultural land.
Increasing temperatures caused by climate change will make the water of the oceans expand; ice melting in the Antarctic and Greenland will also contribute to the sea level. Sea levels could rise by as much as 25 to 50 cm, by 2100. Greater sea levels will threaten the low-lying coastal areas such as the Netherlands and Bangladesh, millions of areas of land will be at danger from flooding; causing people to leave their homes. Low lying areas in cities will be hugely affected by the rising sea.
Changes in weather will affect many crops grown around world. Crops such as wheat and rice grow well in high temperatures, while plants such as maize and sugarcane prefer cooler climates. Changes in rainfall patterns will also affect how well plants and crops grow. The effect of a change in the weather on plant growth may lead to some countries not having enough food. Brazil, parts of Africa, south-east Asia and China will be affected the most and many people could be affected by hunger.
All across the world, there is a big demand for water and in many regions, such as the central and eastern Africa there is not enough water for the people. Changes in the climate will change the weather patterns and will bring more rain in some countries, but others will have less rain, generally dry areas will become drier and wet areas could become wetter.
As climate change takes place, our daily weather and normal temperatures will change, the homes of plants and animals will be affected all over the world. Polar bears and seals are a good example of animals that will be affected by climate change, they will have to find new land for hunting and living, if the ice in the Arctic melts, but the fact is more real that these species could become extinct.

Long-Term Climatic Change

Climates change over extremely long periods of time

Ice Ages – Periods of extensive glacial coverage

5 Most recent ended

10,000 years ago

7 Temps dropped 5°C

Short-Term Climatic Change

Caused by regular variations in daylight, temp, and weather patterns

Examples:

11 Seasons

12 El Nino (Warm ocean current)

What Is Abrupt Climate Change?

The United States Climate Change Science Program defines abrupt climate change as “a change in the climate (for example, in temperature or precipitation) that takes place over a few decades or less, persists for at least a few decades, and causes substantial disruptions in human and natural systems.” Abrupt climate change may affect the entire globe or just a region.

Abrupt climate change refers to a sudden, rapid change from one climate state to another (over a period of years rather than centuries or millennia).

Comparison chart

| |Climate |Weather |
|Definition |Describes the average conditions expected at a specific place at a |Describes the atmospheric conditions at a specific place at|
| |given time. A region's climate is generated by the climate system, |a specific point in time. Weather generally refers to |
| |which has five components: atmosphere, hydrosphere, cryosphere, land|day-to-day temperature and precipitation activity |
| |surface, and biosphere. | |
|Components |Climate may include precipitation, temperature, humidity, sunshine, |Weather includes sunshine, rain, cloud cover, winds, hail, |
| |wind velocity, phenomena such as fog, frost, and hail storms over a |snow, sleet, freezing rain, flooding, blizzards, ice |
| |long period of time. |storms, thunderstorms, steady rains from a cold front or |
| | |warm front, excessive heat, heat waves and more |
|Forecast |By aggregates of weather statistics over periods of 30 years |By collecting meteorological data, like air temperature, |
| | |pressure, humidity, solar radiation, wind speeds and |
| | |direction etc. |
|Determining factors |Aggregating weather statistics over periods of 30 years ("climate |By collecting meteorological data, like air temperature, |
| |normals"). |pressure, humidity, solar radiation, wind speeds and |
| | |direction etc. |
|About |Climate is defined as statistical weather information that describes|Weather is the day-to-day state of the atmosphere, and its |
| |the variation of weather at a given place for a specified interval. |short-term (minutes to weeks) variation |
|Time period |Measured over a long period |Measured for short term |
|Study |Climatology |Meteorology |