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1:53 Impact of climate change

Weather is the state of the atmosphere, describing for example how hot or cold it is, how wet or dry it is, how calm or stormy it is, how clear or cloudy it is.[1] On Earth, most weather occurs in the lowest layer of the planet's atmosphere, the troposphere,[2][3] just below the stratosphere. Weather refers to daily temperature, precipitation, and other atmospheric conditions, while climate is the term for the average of atmospheric conditions over long periods of time.[4] When used without qualification, /"weather" is generally understood to refer to Earth's weather.

Weather is determined by differences in atmospheric pressure, temperature, and humidity between one location and another. These differences can occur because of the angle of the Sun at a particular location, which varies with latitude. The strong temperature contrast between polar and tropical air gives rise to the larger-scale atmospheric circulations: the Hadley cell, the Ferrel cell, the polar cell, and the jet stream. Mid-latitude weather systems, such as extratropical cyclones, are caused by instabilities in the jet stream. Because the Earth's axis is tilted relative to its orbital plane (called the ecliptic), sunlight falls at different angles at different times of the year. On the Earth's surface, temperatures typically vary by ±40 °C (-40 °F to 104 °F) per year. Over thousands of years, changes in Earth's orbit can affect the amount and distribution of solar energy received by Earth, thereby influencing long-term climate and global climate change.

Surface temperature differences in turn cause pressure differences. Higher altitudes are colder than lower altitudes, because most of the atmospheric warming is due to contact with the Earth's surface, while radiative losses to space are mostly constant. Weather forecasting is the application of science and technology to predict the state of the atmosphere at a future time and location. The Earth's weather system is a chaotic system; therefore, small changes in one part of the system can grow to have large effects on the system as a whole. Human attempts to control the weather have occurred throughout history, and there is evidence that human activities such as agriculture and industry have altered weather patterns

The study of how climate works on other planets has provided insight into how climate works on Earth. One famous landmark in the Solar System, Jupiter's Great Red Spot, is an anticyclonic storm known to have existed for at least 300 years. However, climate is not limited to planetary bodies. The corona of a star is constantly being shed into space, creating what is essentially a very thin atmosphere throughout the Solar System. The motion of mass ejected from the Sun is known as the solar wind. Climate is the long-term weather pattern of an area, usually averaged over 30 years.[1][2] More rigorously, it is the average and variability of weather variables over a period of months to millions of years.[1] Some of the commonly measured weather variables are temperature, humidity, atmospheric pressure, wind, and precipitation. In a broader sense, climate is the state of the components of the climate system, including the atmosphere, hydrosphere, cryosphere, lithosphere, and biosphere and the interactions between them.[1] The climate of a place is affected by its latitude/longitude, terrain, altitude, land use, and nearby bodies of water and their currents.[3]

Climates can be classified according to average and typical variables, most commonly temperature and precipitation. The most widely used classification system is the Köppen climate classification. The Thornthwaite system[4], in use since 1948, integrates evapotranspiration as well as temperature and precipitation information and is used to study biological diversity and how climate change affects it. Finally, the Bergeron and spatial synoptic classification systems focus on the origin of the air masses that define a region's climate.

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