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)
Volcanoes may have saved an ice-bound Earth.
Dr Iain Stewart describes Snowball Earth, a period of dramatic cooling that may have started 700 million years ago. He explains how the carbon dioxide from volcanoes may have rescued our planet from an icy fate.
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.
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.
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.
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.
Climate is the statistics of weather, usually over a 30-year interval. It is measured by assessing the patterns 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 differs 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, lithosphere, 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 the Köppen climate classification. The Thornthwaite system, in use since 1948, incorporates evapotranspiration along with temperature and precipitation information and is used in studying biological diversity and how climate change effects it. 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. Global warming results in redistributions. For example, "a 3°C change in mean annual temperature corresponds to a shift in isotherms of approximately 300–400 km in latitude (in the temperate zone) or 500 m in elevation. Therefore, species are expected to move upwards in elevation or towards the poles in latitude in response to shifting climate zones".