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 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