Climate variability refers to the climatic parameter of a region varying from its long-term mean. Every year in a specific time period, the climate of a location is different. Some years have below-average rainfall, some have average or above-average rainfall.
For example, the average annual rainfall of Rajshahi in northwestern Bangladesh is 1494 mm. We are not assured of getting this amount every year. The actual rainfall varying from the mean represents drought and flood conditions.
Importance of Climate Variability
Whatever anthropogenic climate changes occur in the future, they will be superimposed on, and interact with, underlying natural variability. Therefore, to anticipate future changes, we must understand how and why climates varied in the past.
This requires well-dated records of forcing factors, as well as paleoclimate; both are available from a variety of natural archives. The greatest barrier to public recognition of human-made climate change is the natural variability of climate.
Factors of Climate Variability
Geographic location & season: Inter-annual variability of surface temperature is larger in the winter hemisphere than in the summer and larger over land than over the ocean. The basic reason for the large winter variability is the huge difference in temperature between low latitudes and high latitudes in winter.
This allows the temperature at a given place to vary by tens of degrees depending on whether the wind is from the south or north. The latitudinal temperature gradient in summer is much smaller, thus providing less drive for exchange of air masses between middle latitudes and polar regions — and when exchange occurs the effect on temperature is less than that caused by a winter ‘polar express’ of Arctic (or the Antarctic) air delivered to middle latitudes
Season & Time: Climate varies over seasons and years instead of day-to-day like the weather. Some summers are colder than others. Some years have more overall precipitation.
Even though people are fairly perceptive of climate variability, it is not as noticeable as weather variability because it happens over seasons and years. Evidence includes statements like: “the last few winters have seemed so short,” or “there seem to be more heavy downpours in recent years.
Causes of Climate Variability
These changes result from atmospheric and oceanic circulation, caused mostly by differential heating of the sun on earth. The atmosphere and ocean circulate in three dimensions and each acts on the other.
The atmosphere moves faster than the ocean, but the ocean stores a large amount of heat and releases it slowly over long periods. Thus, the ocean acts as a memory in this circulation. These atmosphere-ocean circulations cause the climate to vary in season-to-season or year-to-year time periods.
Types of Climate Variability
Variability may result from natural internal processes within the climate system (internal variability) or from variations in natural or anthropogenic external forces (external variability).