The American writer Mark Twain is credited with saying, "climate is what we expect, weather is what we get." Climate is, generally speaking, the "average" weather trend over long time periods.
Natural processes have changed the Earth's climate dramatically over the last 4.6 billion years. Volcanoes, the energy output of the Sun, the tilt and orbit of the planet relative to the Sun, and the movement of the continents are some of the factors that influence the climate.
Human activities such as burning coal and driving automobiles add greenhouse gases to the ones naturally present in the atmosphere and potentially warm the atmosphere more than normal. Scientists are currently trying to predict the extent of this manmade climate change. Visit BBC Weather to learn more about climate science.
Image: A satellite image indicating Pacific Ocean water temperatures associated with El Niño, a periodic climate pattern. (credit: NASA/JPL)
A methane surge in the oceans 55 million years ago warmed the Earth.
Professor Iain Stewart explains how a surge in methane, a greenhouse gas, emitted from the oceans 55 million years ago caused global warming. He describes how the rise of the Himalayas helped to bring this cooling to an end - weathering of this mighty mountain range took carbon dioxide out of the atmosphere. The exact cause of the methane surge 55 million years ago is uncertain.
Many of the world's glaciers are retreating.
Dr Iain Stewart describes the retreat of many of the Earth's glaciers and the break up of polar ice sheets.
We are living in an age of ice.
Dr Iain Stewart explains that we are living during a relatively warm period of an ice age.
Ice is an important factor that governs the Earth's climate.
Dr Iain Stewart explains how the Earth's ice plays an important role in controlling the climate.
Iain Stewart explains why heavy rains only come in the summer.
Professor Iain Stewart explains why India's intense monsoon rains only last for three months a year in the summer.
Climate is a measure of the average pattern of variation in temperature, humidity, atmospheric pressure, wind, precipitation, atmospheric particle count and other meteorological variables in a given region over long periods of time. Climate is different from weather, in that weather only describes the short-term conditions of these variables in a given region.
A region's climate is generated by the climate system, which has five components: atmosphere, hydrosphere, cryosphere, land surface, and biosphere.
The climate of a location is affected by its latitude, terrain, and altitude, as well as nearby water bodies and their currents. Climates can be classified according to the average and the typical ranges of different variables, most commonly temperature and precipitation. The most commonly used classification scheme was originally developed by Wladimir Köppen. The Thornthwaite system, in use since 1948, incorporates evapotranspiration along with temperature and precipitation information and is used in studying animal species diversity and potential effects of climate changes. The Bergeron and Spatial Synoptic Classification systems focus on the origin of air masses that define the climate of a region.
Paleoclimatology is the study of ancient climates. Since direct observations of climate are not available before the 19th century, paleoclimates are inferred from proxy variables that include non-biotic evidence such as sediments found in lake beds and ice cores, and biotic evidence such as tree rings and coral. Climate models are mathematical models of past, present and future climates. Climate change may occur over long and short timescales from a variety of factors; recent warming is discussed in global warming.