Climate variability
Climate variability refers to the natural fluctuations in climate conditions over time within a specific geographic area. This concept encompasses changes in temperature, precipitation, humidity, and other meteorological elements that occur over extended periods, typically measured in decades to centuries. While these variations are an inherent part of Earth's climate system, distinguishing them from long-term climate change is crucial for accurate historical evaluations and future projections.
The magnitude of climate variability can be assessed through statistical differences in long-term weather data and is often characterized by anomalies—deviations from established climatic norms. The properties of climate include thermal, kinetic, and static aspects, which are interrelated through various physical processes. Historically, climate has exhibited significant variability, such as the warmer periods experienced a thousand years ago, followed by colder spells like the Little Ice Age.
In the context of modern climate change, recent trends indicate a concerning rise in global temperatures attributed primarily to human-induced greenhouse gas emissions. This has led to increased occurrences of extreme weather events and rising sea levels, particularly affecting vulnerable regions like the Arctic. Understanding climate variability is essential for communities to adapt and respond effectively to ongoing climatic changes and challenges.
Climate variability
A stable climate is not necessarily a static climate: Climates can vary within limits over time, and it is important to distinguish between this climate variability and genuine climate change in evaluating climatic history and making future projections.
Background
Climate is an abstraction, a synthesis of the day-to-day weather conditions in a given area over a long period of time. The main climate elements are precipitation, temperature, humidity, sunshine, radiation, wind speed, wind direction, and phenomena such as fog, frost, thunder, gales, cloudiness, evaporation, and grass and soil temperatures. In addition, meteorological elements observed in the upper air may be included where appropriate. The climate of any area may also be described as a statistical analysis of weather and atmospheric patterns, such as the frequency or infrequency of specific events.
In the most general sense, the term “climate variability” denotes the inherent tendency of the climate of a specific area to change over time. The time period considered would normally be at least fifty years, but a period of at least one hundred years is usually more appropriate. Instrumental climatic observations have been taken in most areas of the world for at least one hundred years, and in some areas for more than two hundred years, and any analysis of climate variability over time should utilize the full record of those observations. Longer time periods, from one thousand years to a geological period, may also be studied using proxies.
Magnitude of Climate Variability
The degree or magnitude of climate variability can best be described through the statistical differences between long-term measurements of meteorological elements calculated for different periods. In this sense, the measure of climate variability is essentially the same as the measure of climate change. The term climate variability is also used to describe deviations of the climate statistics over a period of time (such as a month, season, or year) from the long-term statistics relating to the same calendar period. In this sense, the measure of climate variability is generally termed a climate anomaly.
Climate Properties
Three basic properties characterize the climate of an area. Thermal properties include surface air temperatures above water, land, and ice. Kinetic properties include wind and ocean currents, which are affected by vertical motions and the motions of air masses, aqueous humidity, cloudiness, cloud water content, groundwater, lake lands, and the water content of snow on land and sea ice. Finally, static properties include pressure and density of the atmosphere and oceans, composition of the dry air, of the oceans, and the geometric boundaries and physical constants of the system. These three types of properties are interconnected by various physical processes, such as precipitation, evaporation, infrared radiation, convection, advection, and turbulence. The climate is a complex system, and any consideration of climate variations, especially in terms of global warming, must be carefully evaluated.
Climate Variability Over the Last Thousand Years
One thousand years ago, some—and possibly many—parts of Earth were warm and dry. The Atlantic Ocean and the North Sea were almost free of storms. This was the time of the great Viking voyages. Vineyards flourished in England; in contrast, some frosts occurred in the Mediterranean area, and rivers such as the Tiber in Rome and the Nile in Cairo occasionally froze. This suggests that a shift occurred in the pattern of large-scale European weather systems. However, by about 1200, the benign climate in Western Europe began to deteriorate, and climate extremes characterized the next two centuries. From about 1400 to 1550, the climate grew colder again, and about 1550 a three-hundred-year cold spell known as the Little began. (The term “Little Ice Age” is used differently by different writers. Many use it to refer to the climate cooling from about 1300 to 1850, while others use it for the latter half of that interval, when cooling was greatest, beginning around 1550 or 1600.) Around 1850, the cold temperatures began to moderate, and from about 1900 a relatively steady warming trend (with a few intervening cold periods) occurred in many areas of the world.
Context
The climate has always varied and will continue to vary, but it is important to differentiate internal variations, or changes that do not imply instability, with external variations, which are attributable to forcing. Changes in the intensity of seasons or of rainfall may presage global warming, or they may simply be temporary oscillations within an existing system. The longer the time period under discussion, moreover, the more difficult it is to tell where unidirectional climate change begins or ends.
Climate variability, when seen as an inherent characteristic of Earth’s atmosphere, can be treated as a reason to accept global changes as natural and beyond human control. When seen as a result of human activity, the same variability can be treated as a call to action to reverse global warming. Evaluations of the limits of natural variability are therefore crucial precursors of evaluations of climate change itself. It is evident that people and societies must adapt to climate changes, and those communities that adapt to the varying climate will be in a better position to withstand the climatic variability of the future.
Data from the first two decades of the twenty-first century and into the third indicated a persistent rise in the Earth’s average temperature. According to the National Aeronautics and Space Administration, 2014–2022 were the nine warmest years since record keeping of this data began in 1880. This has resulted in climate change and more extreme weather events such as forest fires, hurricanes, and droughts. This climate variability has been mostly attributed to greenhouse gas emissions exacerbated by human activity. Data suggested the level of emissions had continued to rise through 2024. The most damaging of these gases were carbon dioxide, methane, and nitrous oxide. The area on Earth most impacted was the Arctic region.
By 2024, data indicated that the global mean surface temperature of Earth had grown approximately 1.54 degrees Celsius warmer than in pre-industrial periods. Ocean temperatures were correspondingly assessed to be on an upward trajectory. An important impact of this temperature increase was the rate of rise in ocean sea levels. Data indicated this rate had doubled since 1993.
Key Concepts
- climate change: alterations in long-term meteorological averages in a given region or globally
- climate fluctuations: changes in the statistical distributions used to describe climate states
- climate normals: averages of a climatic variable for a uniform period of thirty years
- climatic oscillation: a fluctuation of a climatic variable in which the variable tends to move gradually and smoothly between successive maxima and minima
- climatic trend: a climatic change characterized by a smooth monotonic increase or decrease of the average value in the period of record
Bibliography
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