climate variability and change climate variability and change climate variability includes all the variations in the climate that last longer than individual weather events, whereas the term climate change only refers to those variations that persist for a longer period of time, typically decades or more. climate change may refer to any time in earth's history, but the term is now commonly used to describe contemporary climate change. since the industrial revolution, the climate has increasingly been affected by human activities. for the human-induced rise in earth's average temperature and its effects, see climate change. atmospheric sciences atmospheric physics atmospheric dynamics (category) atmospheric chemistry (category) meteorology weather (category) · (portal) tropical cyclone (category) climatology climate (category) climate change (category) global warming (category) · (portal) aeronomy aeronomy glossaries glossary of meteorology · glossary of tropical cyclone terms · glossary of tornado terms · glossary of climate change the climate system receives nearly all of its energy from the sun and radiates energy to outer space. the balance of incoming and outgoing energy and the passage of the energy through the climate system is earth's energy budget. when the incoming energy is greater than the outgoing energy, earth's energy budget is positive and the climate system is warming. if more energy goes out, the energy budget is negative and earth experiences cooling. the energy moving through earth's climate system finds expression in weather, varying on geographic scales and time. long-term averages and variability of weather in a region constitute the region's climate. such changes can be the result of "internal variability", when natural processes inherent to the various parts of the climate system alter the distribution of energy. examples include variability in ocean basins such as the pacific decadal oscillation and atlantic multidecadal oscillation. climate variability can also result from external forcing, when events outside of the climate system's components produce changes within the system. examples include changes in solar output and volcanism. climate variability has consequences for sea level changes, plant life, and mass extinctions; it also affects human societies. terminology climate variability is the term to describe variations in the mean state and other characteristics of climate (such as chances or possibility of extreme weather, etc.) "on all spatial and temporal scales beyond that of individual weather events." some of the variability does not appear to be caused by known systems and occurs at seemingly random times. such variability is called random variability or noise. on the other hand, periodic variability occurs relatively regularly and in distinct modes of variability or climate patterns. the term climate change is often used to refer specifically to anthropogenic climate change (also known as global warming). anthropogenic climate change is caused by human activity, as opposed to changes in climate that may have resulted as part of earth's natural processes. in this sense, the term climate change has become synonymous with anthropogenic global warming. within scientific journals, global warming refers to surface temperature increases while climate change includes global warming and everything else that increasing greenhouse gas levels affect. a related term, climatic change, was proposed by the world meteorological organization (wmo) in 1966 to encompass all forms of climatic variability on time-scales longer than 10 years, but regardless of cause. during the 1970s, the term climate change replaced climatic change to focus on anthropogenic causes, as it became clear that human activities had a potential to drastically alter the climate. climate change was incorporated in the title of the intergovernmental panel on climate change (ipcc) and the un framework convention on climate change (unfccc). climate change is now used as both a technical description of the process, as well as a noun used to describe the problem. causes on the broadest scale, the rate at which energy is received from the sun and the rate at which it is lost to space determine the equilibrium temperature and climate of earth. this energy is distributed around the globe by winds, ocean currents, and other mechanisms to affect the climates of different regions. factors that can shape climate are called climate forcings or "forcing mechanisms". these include processes such as variations in solar radiation, variations in the earth's orbit, variations in the albedo or reflectivity of the continents, atmosphere, and oceans, mountain-building and continental drift and changes in greenhouse gas concentrations. external forcing can be either anthropogenic (e.g. increased emissions of greenhouse gases and dust) or natural (e.g., changes in solar output, the earth's orbit, volcano eruptions). there are a variety of climate change feedbacks that can either amplify or diminish the initial forcing. there are also key thresholds which when exceeded can produce rapid or irreversible change. some parts of the climate system, such as the oceans and ice caps, respond more slowly in reaction to climate forcings, while others respond more quickly. an example of fast change is the atmospheric cooling after a volcanic eruption, when volcanic ash reflects sunlight. thermal expansion of ocean water after atmospheric warming is slow, and can take thousands of years. a combination is also possible, e.g., sudden loss of albedo in the arctic ocean as sea ice melts, followed by more gradual thermal expansion of the water. climate variability can also occur due to internal processes. internal unforced processes often involve changes in the distribution of energy in the ocean and atmosphere, for instance, changes in the thermohaline circulation. internal variability climatic changes due to internal variability sometimes occur in cycles or oscillations. for other types of natural climatic change, we cannot predict when it happens; the change is called random or stochastic. from a climate perspective, the weather can be considered random. if there are little clouds in a particular year, there is an energy imbalance and extra heat can be absorbed by the oceans. due to climate inertia, this signal can be 'stored' in the ocean and be expressed as variability on longer time scales than the original weather disturbances. if the weather disturbances are completely random, occurring as white noise, the inertia of glaciers or oceans can transform this into climate changes where longer-duration oscillations are also larger oscillations, a phenomenon called red noise. many climate changes have a random aspect and a cyclical aspect. this behavior is dubbed stochastic resonance. half of the 2021 nobel prize on physics was awarded for this work to klaus hasselmann jointly with syukuro manabe for related work on climate modelling. while giorgio parisi who with collaborators introduced the concept of stochastic resonance was awarded the other half but mainly for work on theoretical physics. ocean-atmosphere variability el niño impacts la niña impacts the ocean and atmosphere can work together to spontaneously generate internal climate variability that can persist for years to decades at a time. these variations can affect global average surface temperature by redistributing heat between the deep ocean and the atmosphere and/or by altering the cloud/water vapor/sea ice distribution which can affect the total energy budget of the earth. oscillations and cycles a climate oscillation or climate cycle is any recurring cyclical oscillation within global or regional climate. they are quasiperiodic (not perfectly periodic), so a fourier analysis of the data does not have sharp peaks in the spectrum. many oscillations on different time-scales have been found or hypothesized: the el niño–southern oscillation (enso) – a large scale pattern of warmer (el niño) and colder (la niña) tropical sea surface temperatures in the pacific ocean with worldwide effects. it is a self-sustaining oscillation, whose mechanisms are well-studied. enso is the most prominent known source of inter-annual variability in weather and climate around the world. the cycle occurs every two to seven years, with el niño lasting nine months to two years within the longer term cycle. the cold tongue of the equatorial pacific ocean is not warming as fast as the rest of the ocean, due to increased upwelling of cold waters off the west coast of south america. the madden–julian oscillation (mjo) – an eastward moving pattern of increased rainfall over the tropics with a period of 30 to 60 days, observed mainly over the indian and pacific oceans. the north atlantic oscillation (nao) – indices of the nao are based on the difference of normalized sea-level pressure (slp) between ponta delgada, azores and stykkishólmur/reykjavík, iceland. positive values of the index indicate stronger-than-average westerlies over the middle latitudes. the quasi-biennial oscillation – a well-understood oscillation in wind patterns in the stratosphere around the equator. over a period of 28 months the dominant wind changes from easterly to westerly and back. pacific centennial oscillation - a climate oscillation predicted by some climate models the pacific decadal oscillation – the dominant pattern of sea surface variability in the north pacific on a decadal scale. during a "warm", or "positive", phase, the west pacific becomes cool and part of the eastern ocean warms; during a "cool" or "negative" phase, the opposite pattern occurs. it is thought not as a single phenomenon, but instead a combination of different physical processes. the interdecadal pacific oscillation (ipo) – basin wide variability in the pacific ocean with a period between 20 and 30 years. the atlantic multidecadal oscillation – a pattern of variability in the north atlantic of about 55 to 70 years, with effects on rainfall, droughts and hurricane frequency and intensity. north african climate cycles – climate variation driven by the north african monsoon, with a period of tens of thousands of years. the arctic oscillation (ao) and antarctic oscillation (aao) – the annular modes are naturally occurring, hemispheric-wide patterns of climate variability. on timescales of weeks to months they explain 20-30% of the variability in their respective hemispheres. the northern annular mode or arctic oscillation (ao) in the northern hemisphere, and the southern annular mode or antarctic oscillation (aao) in the southern hemisphere. the annular modes have a strong influence on the temperature and precipitation of mid-to-high latitude land masses, such as europe and australia, by altering the average paths of storms. the nao can be considered a regional index of the ao/nam. they are defined as the first eof of sea level pressure or geopotential height from 20°n to 90°n (nam) or 20°s to 90°s (sam). dansgaard–oeschger cycles – occurring on roughly 1,500-year cycles during the last glacial maximum ocean current changes a schematic of modern thermohaline circulation. tens of millions of years ago, continental-plate movement formed a land-free gap around antarctica, allowing the formation of the acc, which keeps warm waters away from antarctica. the oceanic aspects of climate variability can generate variability on centennial timescales due to the ocean having hundreds of times more mass than in the atmosphere, and thus very high thermal inertia. for example, alterations to ocean processes such as thermohaline circulation play a key role in redistributing heat in the world's oceans. ocean currents transport a lot of energy from the warm tropical regions to the colder polar regions. changes occurring around the last ice age (in technical terms, the last glacial) show that the circulation is the north atlantic can change suddenly and substantially, leading to global climate changes, even though the total amount of energy coming into the climate system didn't change much. these large changes may have come from so called heinrich events where internal instability of ice sheets caused huge ice bergs to be released into the ocean. when the ice sheet melts, the resulting water is very low in salt and cold, driving changes in circulation. life life affects climate through its role in the carbon and water cycles and through such mechanisms as albedo, evapotranspiration, cloud formation, and weathering. examples of how life may have affected past climate include: glaciation 2.3 billion years ago triggered by the evolution of oxygenic photosynthesis, which depleted the atmosphere of the greenhouse gas carbon dioxide and introduced free oxygen another glaciation 300 million years ago ushered in by long-term burial of decomposition-resistant detritus of vascular land-plants (creating a carbon sink and forming coal) termination of the paleocene–eocene thermal maximum 55 million years ago by flourishing marine phytoplankton reversal of global warming 49 million years ago by 800,000 years of arctic azolla blooms global cooling over the past 40 million years driven by the expansion of grass-grazer ecosystems greenhouse gases co2 concentrations over the last 800,000 years as measured from ice cores (blue/green) and directly (black) whereas greenhouse