Climatology

Climatology is the scientific study of Earth's climate. It is a branch of the Earth sciences that focuses on atmospheric conditions over extended periods. While weather describes the atmosphere during a brief period, climate represents the average of these conditions over at least 30 years. Climatologists study three main areas: climate variability, the mechanisms of climate change, and modern climate change. This field is a subdivision of physical geography and includes aspects of oceanography and biogeochemistry. By understanding these systems, scientists can better comprehend how our planet functions over time.

To understand how climate works, scientists look at the Earth's energy budget. The climate system receives nearly all its energy from the sun. It also releases energy back into outer space. Climate models simulate how the atmosphere, oceans, land surface, and ice interact to manage this energy. These models balance incoming short wave radiation, which includes visible light, with outgoing long wave radiation, or infrared radiation. If these two flows are not in balance, the Earth's average temperature will change. Most models also include the radiative effects of greenhouse gases, such as carbon dioxide, to predict temperature trends.

Climatology is divided into several specialized subfields based on the purpose of the research. The American Meteorological Society identifies three main categories: descriptive, scientific, and applied climatology. Applied climatologists use their expertise to help specific industries, such as manufacturing and agriculture. Other specialized branches include paleoclimatology, which reconstructs past climates using ice cores and tree rings. Scientists practicing dendroclimatology specifically study tree rings to understand history. There is also paleotempestology, which uses ancient records to determine how often hurricanes occurred over millennia. Other branches include hydroclimatology, which studies the water cycle, and bioclimatology.

The history of climate study stretches back to Ancient Greece. The word "climate" comes from the Greek word "klima," meaning "slope." This referred to the inclination of the Earth's axis. Around 400 BCE, Hippocrates wrote "On Airs, Water and Places." This text discussed how climate affects human health and cultural differences. In the 11th century, Chinese scientist Shen Kuo observed petrified bamboos near Yanzhou. Because bamboo needs a wet climate, he inferred that climates had shifted over enormous spans of time. These early observations laid the groundwork for modern climate science.

As technology advanced, scientists began systematic recordkeeping. The invention of thermometers and barometers during the Scientific Revolution was a major turning point. Systematic records began in England around 1640 to 1642. In 1686, Edmund Halley published a map of the trade winds. Later, Benjamin Franklin mapped the Gulf Stream to assist with mail delivery between North America and Europe. In the 20th century, Helmut Landsberg fostered the use of statistical analysis in the field. Today, researchers use a global network of thermometers and Earth-observing satellites to collect massive datasets. This data allows for more precise modeling of complex physical processes.

Climatologists use various methods to analyze the atmosphere. They often use climate indices to represent the status and timing of specific climate factors. These indices simplify complex data into a generalized description of the global system. One example is the El Niño–Southern Oscillation, or ENSO. This is a coupled ocean-atmosphere phenomenon in the Pacific Ocean that drives global temperature variability. Other examples include the North Atlantic oscillation (NAO) and the Madden–Julian oscillation (MJO). The MJO is a cycle occurring in the stratosphere that lasts approximately 30 to 60 days. These patterns help scientists understand the cycles within the larger climate system.

Climate is influenced by many physical factors and geographical features. For instance, tropical regions show very little temperature variation throughout the year. In contrast, midlatitudes experience a pronounced seasonal cycle. Continentality also plays a major role in local climates. This refers to the distance from major water bodies like oceans. Oceans act as a moderating factor for temperature. Land close to an ocean usually has smaller differences between winter and summer temperatures than land far from the sea. Winds also generate ocean currents, which transport heat around the entire globe. This interaction between the atmosphere and the oceans is essential for maintaining the Earth's climate patterns.