# Basic Geography/Climate/Weather Extremes
## Weather Extremes

Weather extremes are the point at which the weather can have a dramatic effect on human activity. The extremes covered in this chapter are:
* Hurricanes (also known as tropical storms, cyclones, or typhoons)
* Droughts

## Hurricanes

The strongest tropical storms are called either hurricanes, typhoons, or cyclones. The different names mean the same thing, but are used in different parts of the world. The term "hurricane" is used to describe storms in the Atlantic and Eastern Pacific oceans.

### How Hurricanes form

Hurricanes need a lot of heat to form, which is why they usually occur over tropical seas. It works like this:
* Rising warm air rises fast, causing towering clouds, heavy rainfall, and intense low pressure.
* The low pressure sucks in air, causing very strong winds which spiral—clockwise in the Northern Hemisphere or anticlockwise on the Southern Hemisphere—around the centre of the low pressure area, at speeds of around 120 km/h (75 mph).
* Seen from above hurricanes are huge circular bodies of thick cloud around 450 km (300miles) wide. The cloud brings heavy rain, thunder, and lightning.
* In the centre is the eye of the hurricane, about 45 km across (30miles) across. Often there will be no cloud in the eye. Seen from below it will seem calmer, with a circle of blue sky above. The eye is formed because this is the only part of the hurricane where air is sinking.
* In the northern hemisphere, the prevailing easterly tropical winds tend to steer hurricanes toward land - although their course is unpredictable. As they move inshore their power gradually reduces, because their energy comes from sucking up moist sea air.

### Effects of Hurricanes

The intense winds of tropical storms can destroy whole communities, buildings, and communication networks. As well as their own destructive energy, the winds generate abnormally high waves and tidal surges, which cause flooding in coastal areas. The most destructive elements are the high seas and the flooding that accompany the storms.

## Droughts

Droughts occur when a long period of abnormally dry weather leads to a severe water shortage. Extreme weather conditions are not the only cause of droughts, however - they are often caused by the activity of man as well. Human activities which can help trigger droughts include:
* Constructing a dam on a large river may help provide electricity and water to irrigate farmland near the reservoir. But it may also cause drought downstream by severely reducing the flow of water.
* Widespread cutting down of trees for fuel reduces the soil's ability to hold water - drying out the ground, triggering desertification, and leading to drought.

### Effects of drought

* Droughts endanger people's lives and livelihoods through thirst, hunger (due to crops dying from lack of water), and the spread of disease.
* Millions of people died in the 20th century due to severe drought and famines. One of the worst hit areas was the Sahel region of Africa, covering parts of Eritrea, Ethiopia, and the Sudan.
* Droughts and famines can have other geographical impacts - for example, forcing people to migrate to a new home, thus putting pressure on resources in neighboring countries.

## Climate change

The climate and weather has always affected Humans in the way we live from everyday climates to the extremes mentioned above. Although throughout the 20th and beginning of the 21st century it has become clear that Humans can affect the climate.

### What is global warming?

The average temperature of the Earth has fluctuated over the past 10,000 years, but has recently been rising. Global warming refers to this rise in the average temperature of the Earth's surface. To understand the way in which humans are contributing to global warming we must first understand the Greenhouse effect.
The greenhouse effect is greenhouse gases acting like a giant blanket around the Earth. This effect is completely natural and it is what keeps the Earth at a comfortable living temperature. The greenhouse gases in the upper atmosphere helps keep some of the heat reflected by the Earth's surface from escaping into space.
Climatologists believe the way humans affect global climate is by the way humans used the world's resources. The theory is that human activities contribute to global warming through the production of greenhouse gases. The main greenhouse gases in the atmosphere are carbon dioxide (CO2), methane, and nitrous oxide. These gases are naturally occurring in atmosphere, but are believed to have increased through burning more fossil fuels, such as oil, petrol, and coal.
Plants use CO2, but, it is argued that man is producing more carbon dioxide than plants can consume. This balance is not helped by deforestation around the world. The gases encourage the atmosphere to retain more radiation from the sun. This is because less radiation is reflected by the outside of the atmosphere, while less heat is released by the atmosphere into space. This therefore increases the temperature of the Earth.

### Impacts of global warming

In the last 100 years it is believed that the average temperature of the earth has risen by 0.6°C. There are estimates that in the next 100 years, the global temperatures could rise by as much as 1.4 to 5.8°C, as a result of global warming. There are several possible effects of such a significant increase in atmospheric temperature.
* Sea levels may rise around the globe by as much as a meter over the next hundred years, caused mainly by the melting of ice caps and glaciers. The islands of Tuvalu in the South Pacific are an example of a place which is already being slowly invaded by the sea. The highest part of the islands is only four meter above sea level.
* Extreme weather conditions will become more common. Many scientists argue that global warming is contributing to an increased frequency of droughts and severe storms such as hurricanes.
* Diseases associated with warm climates - such as malaria - may become prevalent in many more countries.

### Tackling global warming

International efforts have been made to encourage governments to reduce emissions of greenhouse gases. In Kyoto, Japan in 1997, many governments pledged to reduce emissions of greenhouse gases. The treaty has not however been signed by the United States, the largest producer of CO2.
Environmental campaigners encourage consumers to boycott businesses and companies who do not act in a sustainable way. Individuals are also encouraged reduce their personal consumption of resources, that contribute to global warming, by driving smaller cars and making the heating in their houses more efficient.