Hurricanes, tornadoes, droughts, floods, or freezing tempereature – extreme weather – is when something in weather is abnormal and usually causes casualties. It can endanger people's lives or damage their crops or property. The weather at anytime can be described by temperature, wind speed, atmospheric pressure, and precipitation (rain, hail, or snow). The average temperature of the world is about 59ºF (15ºC), but some places are much colder than this, other places much warmer. The average rainfall across the world is 39 in (100 cm) per year. But the rain is not evenly ditributed – some parst of the world have virtually no rain at all, others as much as 36 ft (11 cm) in one year. Also, a particular location may be dry for months and then be soaked by a flood. Often, extreme weather takes people by surprise. Destructive thunderstorms, tornadoes, or floods can happen in places where weather is normally quite calm.



There are many factors that can affect the weather. Among the most important are the heating of the Earth by the sun and differences in atmospheric pressure. Low atmospheric pressure usually means stormy weather. The pressure at the center of a hurricane is extremely low, for example. Other factors, including dust from volcanoes or storms on the sun's surface, can disturb the weather, making it hotter or colder, or increasing or reducing rainfall. Humans can also affect the weather by polluting the atmosphere. Although the causes of extreme weather are well understood, it is still impossible to predict weather more than a few days ahead. This is because. This is because the weather is a complex system that is very sensitive to small disturbances. It has been said that even the beat of a butterfly's wing could affect how the weather develops.

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