Climatology
Climatology is the scientific study of climate, encompassing the long-term patterns and variations of weather conditions in a given area over periods ranging from months to millennia. It is essential for understanding how climatic changes impact all life on Earth, including human societies. Central to climatology is the distinction between weather, which refers to short-term atmospheric conditions, and climate, which reflects average weather patterns over extended timeframes.
Climatologists utilize various tools and methods to gather data on atmospheric phenomena, such as temperature, precipitation, and air pressure, all of which contribute to the Earth's climate system. Notably, the greenhouse effect plays a critical role in regulating Earth's temperature, as certain gases trap heat in the atmosphere. Anthropogenic factors, like greenhouse gas emissions from human activities, have become significant drivers of climate change, resulting in alarming trends in global temperatures and environmental impacts.
Historical efforts in climatology date back centuries, with advancements in measuring instruments and theoretical understanding significantly shaping the field. As climate change continues to pose challenges for ecosystems and human communities, the demand for climatologists and related experts is expected to grow, driven by the need for accurate forecasting and climate mitigation strategies. Understanding climatology is crucial for developing informed responses to the pressing issues of climate variability and change.
Climatology
Summary
Climatology deals with the science of climate, which includes the huge variety of weather events. These events change at periods that range from months to millennia. Climate has such a profound influence on all life forms, including human life, that people have made numerous attempts to predict future climatic conditions. These attempts resulted in research efforts to try to understand future changes in the climate as a consequence of anthropogenic and naturally caused activity.
Definition and Basic Principles
Weather pertains to atmospheric conditions that constantly change, hourly and daily. In contrast, climate refers to the long-term composite of weather conditions at a particular location, such as a city or a state. The climate at a location is based on daily mean conditions that have been aggregated over periods that range from months and years to decades and centuries. Both weather and climate involve measurements of the same conditions—air temperature, water vapor in the air (humidity), atmospheric pressure, wind direction, wind speed, cloud types and extent, and the amount and kind of precipitation.
Estimates of ancient climates, going back several thousand years or more, are produced in various ways. For example, the vast amount of groundwater discovered in southern Libya indicates that during some periods, part of the Sahara Desert was much wetter. In ancient Egypt, stone markers called Nilometers built along the banks of the Nile River were used to gauge the river’s height each year. They are similar to the staff gauges used by the US Geological Survey to indicate stream or canal elevation. The Nilometer's height reflects the extent of precipitation and associated runoff in the headwaters of the Nile in Central Africa.
Background and History
Precipitation measurements and records were kept in India during the fourth century BCE. Precipitation records were kept in Palestine around 100 CE, Korea around the 1440s, and England during the late seventeenth century. Galileo invented the thermometer in the early 1600s. Italian physicist Evangelista Torricelli, who worked with Galileo, invented the barometer in 1643. Physicist Daniel Fahrenheit created a measuring scale for a liquid-in-glass thermometer in 1714, and Swedish astronomer Anders Celsius developed the centigrade scale in 1742.
The first attempt to explain the circulation of the atmosphere around the Earth was made by English astronomer Edmond Halley, who published a paper charting the trade winds in 1686. In 1735, English meteorologist George Hadley further explained the movement of the trade winds, describing what became known as a Hadley cell, and in 1831, Gustave-Gaspard Coriolis developed equations to describe the movement of air on a rotating Earth. In 1856, American meteorologist William Ferrel developed a theory describing the mid-latitude atmospheric circulation cell, or Ferrel cell. In 1860, Dutch meteorologist Christophorus Buys Ballot demonstrated the relationship between pressure, wind speed, and direction, which became known as Buys Ballot's law.
German naturalist Alexander von Humboldt created the first map of average annual isothermslines connecting points having the same temperaturefor the Northern Hemisphere in 1817. In 1848, German meteorologist Heinrich Wilhelm Dove created a world map of average monthly temperatures. In 1845, German geographer Heinrich Berghaus prepared a global map of precipitation. In 1882, the first world map of precipitation using average annual isohyetslines connecting points having the same precipitationappeared.
How It Works
Earth's Global Energy Balance. The Earth's elliptical orbit about the Sun ranges from 91.5 million miles at perihelion (closest to the Sun) in January, to 94.5 million miles at aphelion (farthest from the Sun) in July, averaging 93 million miles. The Earth intercepts about two-billionth of the total energy output of the Sun. Upon reaching the Earth, some incoming radiation is reflected back into space, while the atmosphere, land, or oceans absorb another portion. Over time, the incoming shortwave solar radiation is balanced by a return to outer space of longwave radiation.
The Earth's atmosphere extends to an estimated height of about six thousand miles. Most of it is made up of nitrogen (78 percent by volume) and oxygen (about 21 percent). Of the remaining 1 percent, carbon dioxide (CO2) accounts for about 0.0385 percent of the atmosphere. This is a minute amount, but carbon dioxide can absorb both incoming shortwave radiation from the sun and outgoing longwave radiation from the Earth. The measured increase in carbon dioxide since the early 1900s is a major cause for concern as it is a very good absorber of heat radiation, which adds to the greenhouse effect.
Air Temperature. Air temperature is a fundamental constituent of climatic variation on the Earth. The amount of solar energy the Earth receives is governed by the latitude (from the equator to the poles) and the season. The amount of solar energy reaching low-latitude locations is greater than in higher-latitude sites closer to the poles. Another factor of air temperature is the fivefold difference between the specific heat of water (1.0) and dry land (0.2). Accordingly, areas near the water have more moderate annual temperatures than inland continental locations, which have much greater seasonal differences.
Anthropogenic (human-induced) changes in land cover in addition to aerosols and cloud changes can result in some degree of global cooling, but this is much less than the combined effect of greenhouse gases in global warming. The gases include carbon dioxide from burning fossil fuels (coal, oil, and natural gas), which has been increasing since the second half of the twentieth century. Other gases such as methane (CH4), chlorofluorocarbons (CFCs), ozone (O3), and nitrous oxide (NO3) also create additional warming effects.
Air temperature is measured five feet above the ground surface and generally includes the maximum and minimum observation for a twenty-four-hour period. The average of the maximum and minimum temperature is the mean daily temperature for that particular location.
Earth's Available Water. Water is a tasteless, transparent, and odorless compound essential to all biological, chemical, and physical processes. Almost all the water on the Earth is in the oceans, seas, and bays (96.5 percent), and around 1.74 percent is frozen in ice caps and glaciers. Accordingly, 98.24 percent of the water on Earth is either frozen or too salty and must be thawed or desalinated. About 0.76 percent of the world's water is fresh (not saline) groundwater, but a large portion is found at depths too great to reach by drilling. Freshwater lakes make up 0.007 percent, and atmospheric water is about 0.001 percent of the total. The combined average flows of all the streams on Earth—from tiny brooks to the mighty Amazon River—account for 0.0002 percent of the total.
Air Masses. The lowest layer of the atmosphere is the troposphere, which varies in height from ten miles at the equator and lower latitudes to four miles at the poles. Different types of air masses within the troposphere can be delineated based on their similarity in temperature, moisture, and to a certain extent, air pressure. Air masses develop over continental and maritime locations that strongly determine their physical characteristics. For example, an air mass starting in a cold, dry interior portion of a continent would develop thermal, moisture, and pressure characteristics substantially different from those of an air mass that developed over water. Atmospheric dynamics also allow air masses to modify their characteristics as they move from land to water and vice versa.
Air mass and weather front terminology were developed in Norway during World War I. The Norwegian meteorologists were unable to get weather reports from the Atlantic theater of operations. Consequently, they developed a dense network of weather stations that led to impressive advances in atmospheric modeling.
Greenhouse Effect. Selected gases in the lower parts of the atmosphere trap heat and radiate some of that heat back to Earth. If there was no natural greenhouse effect, the Earth's overall average temperature would be close to 0 degrees Fahrenheit rather than 57 degrees Fahrenheit.
Burning coal, oil, and gas produces carbon dioxidemajor greenhouse gas. Carbon dioxide accounts for nearly half of heat-producing gases in the atmosphere. In mid-eighteenth century Great Britain, before the Industrial Revolution, the estimated level of carbon dioxide was about 280 parts per million (ppm). Estimates for the natural range of carbon dioxide for the past 650,000 years are 180–300 ppm—well below the figures of 399 ppm in 2015 and 420 ppm in 2020. Carbon dioxide emissions accounted for about 80 percent of all the gases that affect climate change in the early 2020s.
The second most important greenhouse gas is methane (CH4), which accounts for about 16 to 25 percent of global emissions. Methane traps heat extremely fast. Over twenty years, methane would trap about eighty times as much heat as carbon dioxide. Methane gas originates from the natural decay of organic matter in wetlands, but anthropogenic activity in the form of rice paddies, manure from farm animals, the decay of bacteria in sewage and landfills, leaks from natural gas production and distribution, and biomass burning (natural and human-induced) doubles the amount produced.
Fluorinated gases such as chlorofluorocarbons (CFCs) absorb longwave energy (warming effect) but also can destroy stratospheric ozone (cooling effect). The warming radiative effect is three times greater than the cooling effect. Fluorinated gases account for less than 5 percent of all climate change factors, but emissions of fluorinated gasses in the United States increased 105 percent between 1990 and 2022. These gasses have long atmospheric lives and are among the most potent greenhouse gasses produced by humans.
Nitrous oxide (N2O) from motor vehicle exhaust and bacterial emissions from nitrogen fertilizers accounted for about 6 percent of all the climate change factors in 2022. Around 40 percent of nitrous oxide emissions result from human activity, primarily agricultural soil management.
Several human actions lead to a cooling of the Earth's climate. For example, burning fossil fuels releases tropospheric aerosols, which scatter incoming solar radiation back into space, thereby lowering the amount of solar energy that can reach the Earth's surface. These aerosols also lead to the development of low and bright clouds that effectively reflect solar radiation back into space.
Applications and Products
Climatology involves the measurement and recording of many physical characteristics of the Earth. Therefore, numerous instruments and methods have been devised to perform these tasks and obtain accurate measurements.
Measuring Temperature. At first glance, obtaining air temperatures appears relatively simple. After all, thermometers have been around since 1714 (Fahrenheit scale) and 1742 (Celsius scale). However, accurate temperature measurements require a white (high-reflectivity) instrument shelter with louvered sides for ventilation, placed where it will not receive direct sunlight. The standard height for the thermometer is five feet above the ground.
Remote-Sensing Techniques. Oceans cover about 71 percent of the Earth's surface, which means that large portions of the world do not have weather stations and places where precipitation can be measured with standard rain gauges. To provide more information about precipitation in the equatorial and tropical parts of the world, the National Aeronautics and Space Administration (NASA) and the Japanese Aerospace Exploration Agency began a program called the Tropical Rainfall Monitoring Mission (TRMM) in 1997. The TRMM satellite monitors the area of the world between 35 degrees north and 35 degrees south latitude. The study’s goal is to obtain information about the extent of precipitation, its intensity, and length of occurrence. The major instruments on the satellite include radar to detect rainfall, a passive microwave imager that can acquire data about precipitation intensity and the extent of water vapor, and a scanner that can examine objects in the visible and infrared portions of the electromagnetic spectrum. The goal of collecting this data is to obtain the necessary climatological information about atmospheric circulation in this portion of the Earth to develop better mathematical models for determining large-scale energy movement and precipitation.
Geostationary Satellites. Geostationary orbiting earth satellites (GOES) enable researchers to view images of the planet from what appears to be a fixed position. To achieve this, these satellites circle the globe at a speed that is in step with the Earth's rotation. This means the satellite, at an altitude of 22,200 miles, will make one complete revolution in the same twenty-four hours and direction that the Earth is turning above the Equator. At this height, the satellite is in a position to view nearly half the planet at any time. On-board instruments can be activated to look for special weather conditions such as hurricanes, flash floods, and tornadoes. The instruments can also be used to make estimates of precipitation during storm events.
Rain Gauges. The accurate measurement of precipitation is more complex than it appears. Collecting rainfall and measuring it is complicated by the possibility of debris, dead insects, leaves, and animal intrusions. Standards were established, although the various national climatological offices use more than fifty types of rain gauges. The location of the gauge, its height above the ground, the possibility for splash and evaporation, its distance from trees, and turbulence all impact the results. Accordingly, all gauge records are estimates. Precipitation estimates are also affected by the number of gauges per unit area. The number of gauges in a sample area of 3,860 square miles for Britain, the United States, and Canada is 245, 10, and 3, respectively. Although the records are reported to the nearest 0.01 inch, discrepancies occur in official records. It is important to have a sufficiently dense network of rain gauges in urban areas. According to some experts, five to ten gauges per 100 square miles are necessary to obtain an accurate measure of rainfall.
Doppler Radar.Doppler radar was first used in England in 1953 to pick up the movement of small storms. The basic principle behind Doppler radar is that the back-scattered radiation frequency detected at a certain location changes over time as the target, such as a storm, moves. The mode of operation requires a transmitter that is used to send short but powerful microwave pulses. When a foreign object (or target) is intercepted, some outgoing energy is returned to the transmitter, where a receiver can pick up the signal. An image (or echo) from the target can then be enlarged and shown on a screen. The target's distance is revealed by the time between transmission and return. The radar screen can indicate where the precipitation is occurring and its intensity by the amount of the echo's brightness. Doppler radar has developed into a very useful device for determining the location of storms and the intensity of the precipitation and for obtaining good estimates of the total amount of precipitation.
Careers and Course Work
Although many consider meteorologists to be people who forecast weather, the better title for such a person is an atmospheric scientist. For example, climatologists focus on climate change, and environmental meteorologists are interested in air quality. Broadcast meteorologists work for television stations. The largest number of jobs in the field are with the National Weather Service.
Employment at weather stations generally requires a bachelor's degree in meteorology, or at least twenty-four credits in meteorology courses along with college physics and physical science classes. Anyone who wants to work in applied research and development needs a master's degree. Research positions require a doctorate.
Social Context and Future Prospects
Literally speaking, climate change may be caused by natural internal and external processes in the Earth-Sun system and human-induced changes in land use and the atmosphere. However, the United Nations Framework Convention on Climate Change states that the term climate change should refer to anthropogenic changes that affect the atmosphere’s composition as distinguished from natural causes, which should be called climate variability. An example of natural climate variability is the global cooling of about 0.5 degrees Fahrenheit in 1992–1993, which was related to the 1991 Mount Pinatubo volcanic eruption in the Philippines. The 15 million to 20 million tons of sulfuric acid aerosols released into the stratosphere reflected incoming radiation from the sun and created a cooling effect. Experts agree that climate change is caused by human activity, as evidenced by the above-normal temperatures in the 2000s. Based on various techniques that estimate temperatures in previous centuries, the years 2019, 2020, and 2021 were among the seven hottest years ever recorded. According to the National Oceanic and Atmospheric Administration's (NOAA) National Centers for Environmental Information (NCEI) analysis, 2023 was the warmest year in their 174-year record.
Numerous observations strongly suggest a continuing warming trend. Snow and ice have retreated from areas such as Mount Kilimanjaro, which at 19,340 feet is the highest mountain in Africa, and glaciated areas in Switzerland. In the Special Report on Emission Scenarios (2000), the Intergovernmental Panel on Climate Change examined the broad spectrum of possible concentrations of greenhouse gases by examining the growth of population and industry along with the efficiency of energy use. The panel estimated future trends using computer climate models. They estimated that global temperature would increase 35.2–39.2 degrees Fahrenheit by the year 2100. By 2023, the global temperature had increased by around 2.45 degrees Fahrenheit (or 1.36 degrees Celsius).
Given the effect climate change will have on humanity, many agencies and organizations continue researching in the area, and climatologists are likely to be increasingly needed by various governmental and private entities. Other factors leading to an increased need for atmospheric scientists include improved technology that enhances forecast accuracy and an increase in the use of wind and solar power by utility companies which relies more heavily on weather forecasting.
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