Climate
Climate represents the long-term weather patterns of a region, typically averaged over 30 years. It encompasses the mean and variability of meteorological variables across time spans ranging from months to millions of years, including temperature, humidity, atmospheric pressure, wind, and precipitation.
Definition Establishes Scientific Framework
Climate derives from the Ancient Greek word κλίμα meaning ‘inclination.’ While often described simply as “average weather,” the concept carries more scientific precision. The Intergovernmental Panel on Climate Change (IPCC) defines climate as “the statistical description in terms of the mean and variability of relevant quantities over a period ranging from months to thousands or millions of years.”
The World Meteorological Organization (WMO) established the concept of “climate normals” as reference points that help climatologists compare current trends with past patterns. These normals represent the arithmetic average of climate elements over a 30-year period—long enough to filter out temporary anomalies like El Niño–Southern Oscillation but short enough to reveal longer climatic trends.
The distinction between climate and weather boils down to a simple concept: “Climate is what you expect, weather is what you get.” Climate represents the broader patterns we can predict, while weather captures the day-to-day variations we experience.
Historical Development Shows Evolving Understanding
The scientific approach to climate study has deep roots. The International Meteorological Organization formed a technical commission for climatology in 1929. At its 1934 Wiesbaden meeting, this commission designated 1901-1930 as the first reference timeframe for climatological standard normals. The WMO later updated these normals based on data from 1961-1990, which now serves as the baseline reference period.
Modern climate measurements track more than just temperature and rainfall. Scientists collect data on humidity, visibility, cloud coverage, solar radiation, soil temperature, evaporation rates, and even days with thunder or hail to build a comprehensive picture of changing climate conditions.
Climate Classification Organizes Global Patterns
Scientists have developed various systems to categorize the world’s climates. These classification schemes help us understand regional patterns and often correlate with biome classifications, since climate heavily influences the life forms in any region.
The Köppen climate classification, first developed in 1899, remains one of the most widely used systems. Classification methods generally fall into two categories:
- Genetic methods focus on the causes of climate, such as air mass types or locations within weather disturbances
- Empiric methods concentrate on climate effects, like plant hardiness zones or evapotranspiration patterns
A common limitation of these classification systems is their tendency to create sharp boundaries between climate zones, whereas nature typically presents more gradual transitions.
Record Preserves Climate History
Paleoclimatology Reveals Ancient Patterns
Paleoclimatology studies Earth’s climate history over vast timescales. Scientists examine evidence from ice sheets, tree rings, sediments, pollen, coral, and rocks to reconstruct past climate conditions. These records reveal both periods of stability and significant change, helping scientists identify patterns like regular climate cycles.
Modern Instruments Capture Recent Changes
Our understanding of recent climate comes from measurements taken with instruments like thermometers, barometers, and anemometers over the past few centuries. When studying historical climate data, scientists must account for changes in instrument technology, observation frequency, known error margins, and exposure conditions.
Long-term modern climate records have historically favored population centers and wealthy countries. Since the 1960s, satellite technology has expanded our ability to gather climate data globally, including remote regions like the Arctic and oceans where human presence is minimal.
Climate Variability Creates Natural Fluctuations
Climate variability describes variations in the mean state and other climate characteristics “on all spatial and temporal scales beyond individual weather events.” Some variations occur randomly, while others follow periodic patterns or distinct climate modes.
Scientists have identified correlations between Earth’s climate oscillations and various factors:
- Astronomical influences (barycenter changes, solar variation, cosmic ray flux)
- Cloud albedo feedback
- Milankovitch cycles
- Heat distribution between oceans and atmosphere
Natural climate oscillations can sometimes be masked by significant volcanic eruptions, impact events, irregularities in climate proxy data, positive feedback processes, or human emissions of substances like greenhouse gases.
The terminology around climate has evolved over time. In the 1960s, “climate change” described what we now call climate variability—natural climatic inconsistencies and anomalies.
Climate Change Transforms Global Systems
Climate change refers to variations in global or regional climates over time, reflecting changes in atmospheric conditions across decades to millions of years. These changes stem from Earth’s internal processes, external forces like variations in sunlight intensity, or human activities.
Scientists have identified Earth’s Energy Imbalance (EEI) as a fundamental metric for tracking global change. In contemporary environmental policy discussions, “climate change” often specifically refers to modern climate shifts, including the rise in average surface temperature known as global warming.
Earth has experienced periodic climate shifts throughout its history, including four major ice ages with glacial periods (colder than normal) separated by interglacial periods. During glacial periods, accumulated snow and ice increase surface albedo, reflecting more solar energy into space and maintaining lower temperatures. Increased greenhouse gases, such as from volcanic activity, can raise global temperature and trigger interglacial periods.
Natural climate changes occur much more slowly than the current rate of change driven by human greenhouse gas emissions. According to the EU’s Copernicus Climate Change Service, average global air temperature exceeded 1.5°C of warming for the period from February 2023 to January 2024.
Climate Models Predict Future Scenarios
Climate models use quantitative methods to simulate interactions between atmosphere, oceans, land surface, and ice through physics equations. These models balance incoming energy (short wave electromagnetic radiation) with outgoing energy (long wave infrared radiation). Any imbalance results in temperature changes.
Models vary in resolution from over 100 km to as fine as 1 km. High-resolution global climate models require substantial computing power. Global models can be downscaled to regional models through dynamic or statistical methods to analyze local climate change impacts. Examples include ICON or mechanistically downscaled data like CHELSA (Climatologies at high resolution for the earth’s land surface areas).
Recent applications have focused on projecting the consequences of increasing atmospheric greenhouse gases, particularly carbon dioxide. These models predict rising global mean surface temperatures, with the most rapid warming expected in the higher latitudes of the Northern Hemisphere.
Climate models range from simple to complex:
- Simple models treat Earth as a single point and average outgoing energy
- More complex models expand vertically (radiative-convective models) or horizontally
- The most sophisticated coupled atmosphere-ocean-sea ice global climate models solve full equations for mass and energy transfer and radiant exchange
Through these models, scientists work to understand our planet’s past climate patterns and project its future under various scenarios, providing crucial information for environmental policy decisions worldwide.
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Climate is the long-term weather pattern in a region, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorological variables that are commonly measured are temperature, humidity, atmospheric pressure, wind, and precipitation. In a broader sense, climate is the state of the components of the climate system, including the atmosphere, hydrosphere, cryosphere, lithosphere and biosphere and the interactions between them. The climate of a location is affected by its latitude, longitude, terrain, altitude, land use and nearby water bodies and their currents.
Climates can be classified according to the average and typical variables, most commonly temperature and precipitation. The most widely used classification scheme is the Köppen climate classification. The Thornthwaite system, in use since 1948, incorporates evapotranspiration along with temperature and precipitation information and is used in studying biological diversity and how climate change affects it. The major classifications in Thornthwaite's climate classification are microthermal, mesothermal, and megathermal. Finally, the Bergeron and Spatial Synoptic Classification systems focus on the origin of air masses that define the climate of a region.
Paleoclimatology is the study of ancient climates. Paleoclimatologists seek to explain climate variations for all parts of the Earth during any given geologic period, beginning with the time of the Earth's formation. Since very few direct observations of climate were available before the 19th century, paleoclimates are inferred from proxy variables. They include non-biotic evidence—such as sediments found in lake beds and ice cores—and biotic evidence—such as tree rings and coral. Climate models are mathematical models of past, present, and future climates. Climate change may occur over long and short timescales due to various factors. Recent warming is discussed in terms of global warming, which results in redistributions of biota. For example, as climate scientist Lesley Ann Hughes has written: "a 3 °C [5 °F] change in mean annual temperature corresponds to a shift in isotherms of approximately 300–400 km [190–250 mi] in latitude (in the temperate zone) or 500 m [1,600 ft] in elevation. Therefore, species are expected to move upwards in elevation or towards the poles in latitude in response to shifting climate zones."
English
Etymology
From Middle English climat, from Old French climat, from Latin
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