Climate Variability refers to departures from the mean position and higher order statistics such as standard deviations, as well as changes in the occurrences of extremes. Moreover, it is used to indicate departures of the mean etc over a given time period (for instance a month, a season, a year) from the long term statistic for a matching time period. Climate variability is thus a measure of the departures which are usually called anomalies. Climate variability is caused by natural occurring internal processes which occur on all time and spatial scales outside of that of individual weather events, and involves many modes of variability involving components of the climate systems such as the atmosphere and the ocean. An example of a naturally occurring internal process which drives climate variability in Trinidad and Tobago is the coupled ocean/atmosphere El Nino-Southern Oscillation (ENSO- El Nino or La Nina) phenomenon.
Climate change refers to a change in the mean condition of the climate that can be identified by a change in the mean and or variability of its properties that is statistically significant and this change must continue for an extended period, typically decades or longer. It may be due to naturally occurring internal processes such as volcanic eruptions which can act to cool the atmosphere; or external forcing such as changes in solar radiation received at the earth surface which can be influenced for instance by change in the tilt of the earth axis away from its orbital plane which occurs naturally. Naturally occurring climate variability can also induce climate change. Climate change may also be due to persistent external influences which do not occur naturally such as the change in the composition of the atmosphere or change in land use generated by human activity such as the burning of fossil fuel and deforestation.
The major difference between climate variability and climate change is the persistent nature of the anomaly and the fact that the change cannot be explained by naturally occurring internal variability processes alone. For instance, rare events occur more often or less often e.g. the maximum temperatures increasingly breaking records each year or nights are consistently becoming warmer each year. Climate change detection is the process of demonstrating that the climate has changed in some defined statistical sense without providing a reason for the change. Climate change attribution is the process of establishing the most likely cause for the detected change with some defined level of confidence.