Changes in population size

 

The size of the population in areas is continuously changing.

These changes are caused by different factors:

1 - Births and deaths are natural causes of population change. 

Births - usually measured using the birth rate (number of live births per 1,000 of the population per year). Deaths - usually measured using the death rate (number of deaths per 1,000 of the population per year). The difference between the birth rate and the death rate of a country or place is called the natural increase. The natural increase is calculated by subtracting the death rate from the birth rate.

natural increase = birth rate - death rate

2 – Migration is a cause of population change. Migration is the movement of people within or between areas. Migration occurs at all scale levels.

• An emigrant is a person who leaves one country to settle permanently in another. Emigration describes the move relative to the departure.

• An immigrant is a person who enters a country to settle permanently in another. Immigration describes the move relative to the point of destination.

Polder landscape

World Distribution of Natural Vegetation

Tourism in the Alps







Climate & Atmospheric circulation

Hadley, Ferrel and Polar Cell

These terms are related to the general circulation of the atmosphere. In this circulation there are three cells of vertical circulation. Try to picture a cross-section of the earth. At the equator the air rises with heating and in the upper atmosphere begins to flow toward the north. At about 30 degrees north latitude it sinks and flows back toward the equator forming the easterlies in the band from 30 N to the equator. This cell is the Hadley circulation.

Between 30 N and about 60 N there is a similar circulation but in a reverse mode. It flows at the surface from 30 N to 60 N where it rises along the Polar front and returns aloft by flowing southward where it sinks at 30N. This cell is called the Ferrel cell.

Finally, north of 60 N there is the Polar cell which in the upper atmosphere flows toward the Pole where it sinks and flows southward near the surface.

Where the Ferrell and Hadley cells sink at 30 N we have an area of generally high pressure. The Ferrell cell flow at the surface is the cause of the westerlies. And with the Polar cell the surface winds are called the polar easterlies. This same pattern is repeated in the southern hemisphere.

Acid Rain

Acid rain is rain that has been made acidic by certain pollutants in the air. Acid rain is a type of acid deposition, which can appear in many forms. Wet deposition is rain, sleet, snow, or fog that has become more acidic than normal. Dry deposition is another form of acid deposition, and this is when gases and dust particles become acidic. Both wet and dry deposition can be carried by the wind, sometimes for very long distances. Acid deposition in wet and dry forms falls on buildings, cars, and trees and can make lakes acidic. Acid deposition in dry form can be inhaled by people and can cause health problems in some people. What is acidity? Acidic and basic are two ways that we describe chemical compounds. Acidity is measured using a pH scale. A pH scale runs from zero (the most acidic) to 14 (the most basic or alkaline). A substance that is neither basic or acidic is called "neutral", and this has a pH of 7.

How pH is measured

How pH is measured
There are many high-tech devices that are used to measure pH in laboratories. One easy way that you can measure pH is with a strip of litmus paper. When you touch a strip of litmus paper to something, the paper changes color depending on whether the substance is acidic or basic. If the paper turns red, the substance is acidic, and if it turns blue, the substance is basic.





Acid Rain and the pH Scale
The pH scale measures how acidic an object is. Objects that are not very acidic are called basic. The scale has values ranging from zero (the most acidic) to 14 (the most basic). As you can see from the pH scale above, pure water has a pH value of 7. This value is considered neutral—neither acidic or basic. Normal, clean rain has a pH value of between 5.0 and 5.5, which is slightly acidic. However, when rain combines with sulfur dioxide or nitrogen oxides—produced from power plants and automobiles—the rain becomes much more acidic. Typical acid rain has a pH value of 4.0. A decrease in pH values from 5.0 to 4.0 means that the acidity is 10 times greater.

Enhanced greenhouse effect

There are two meanings of the term greenhouse effect.

1. There is a natural greenhouse effect that keeps the Earth's climate warm and habitable.
2. There is also the man-made enhanced greenhouse effect, which is the enhancement of Earth's natural greenhouse effect by the addition of greenhouse gases from the burning of fossil fuels (mainly petroleum, coal, and natural gas).

In order to understand how the greenhouse effect operates, we need to first understand infrared radiation. Greenhouse gases trap some of the infrared radiation that escapes from the Earth, making the Earth warmer that it would otherwise be. You can think of greenhouse gases as sort of a blanket for infrared radiation. It keeps the lower layers of the atmosphere warmer, and the upper layers colder, than if the greenhouse gases were not there.

About 80-90% of the Earth's natural greenhouse effect is due to water vapour, a strong greenhouse gas. The remainder is due to carbon dioxide, methane, and a few other minor gases.

It is the carbon dioxide concentration that is increasing, due to the burning of fossil fuels (as well as from some rainforest burning). This is the man-made portion of the greenhouse effect, and it is believed by many scientists to be responsible for the global warming of the last 150 years.

Greenhouse gases

By their percentage contribution to the greenhouse effect on Earth the four major gases are:

• water vapour, 36–70%
• carbon dioxide, 9–26%
• methane, 4–9%
• ozone, 3–7%