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Climate maps show changes in climate in a geographic area, including overall climate, seasonal variations, and past and future climates. The most widely used classification system is the Koppen system, which divides climates into five main categories and 30 subcategories. Climate maps can also illustrate specific seasons and factors such as temperature and precipitation. They can be used to reconstruct past climates and create maps of other planets such as Mars.
A climate map represents changes in climate in a geographic area. It can cover the entire planet, a single continent, or a smaller region. Climate maps can show overall climate according to a classification system based on averages or a single factor, such as temperature or precipitation. They can also show seasonal variations, predictions of future climates, or reconstructions of past climates.
Various climate classification systems can be employed to produce a world climate map that defines distinct climate regions, but the most widely used method was developed in the early 1900s by German-Russian climatologist Wladimir Koppen. It is based on average annual and monthly temperature and rainfall, and the resulting regions are closely related to vegetation zones. This system was frequently modified by Koppen himself and, later, by others.
The Koppen system divides climates into five main categories, denoted by capital letters A through E. “A” represents a humid tropical climate, with high temperatures and high rainfall throughout the year; “B” is a dry climate, with low rainfall throughout the year, divided into semi-arid “S” type and arid “W” type; “C” is a humid climate in the middle latitudes; “D” is a continental climate with relatively low rainfall and large seasonal variations in temperature and “E” is a polar climate, with low temperatures throughout the year. Sometimes an “H” category is added to indicate a mountain climate, which applies to high mountain regions such as the Himalayas.
A second lowercase letter has been added to create subcategories based on seasonal precipitation patterns, for example “s” denotes a dry summer season. Not all of these subcategories apply to all major climate types. A third lowercase letter has been added to further subdivide some climate categories based on seasonal temperature patterns, for example, “a” indicates a hot summer, with average temperatures above 72°F (22°C). Again, not all of these apply to all climate types. In all, this system creates 30 climate types that can be illustrated in different colors in a map of climate regions.
Specific seasons can be illustrated in a climate map, showing, for example, the variability in temperature or precipitation throughout the year. Lines can be drawn connecting points that have the same value for a given factor to produce a “contour” map showing the high and low areas for this factor. For example, lines connecting points of equal temperature are called isotherms, so a map with isotherms can show temperature variations within a region or the planet as a whole at a glance. A series of maps for different times of the year can illustrate seasonal variations.
Concern about climate change has led to the creation of climate maps showing possible future climates. These use projections based on the estimated overall temperature increases that would result from various levels of carbon dioxide production. One such map shows the effects of an overall increase in global temperature of 39.2°F (4°C). It is thought that temperatures would increase more over land than over the oceans, and that the increases would be greater at high latitudes than at low latitudes. These maps can also illustrate geographic change due to sea level rise.
It is possible to reconstruct past climates using fossils and other evidence. For example, the analysis of pollen grains in ancient soil samples can indicate the types of vegetation present at the time of soil formation, giving a good indication of the type of climate up to a few tens of thousands of years ago. Going further back into the past, fossil evidence of plant remains, examples of glaciation – indicating a cold climate – or aeolian erosion – indicating a dry climate – can provide insight into climates dating back hundreds of millions of years, allowing maps climatic past to be created.
Climate maps for the planet Mars have also been produced. They are much simpler than maps illustrating the Earth’s climate since there are no oceans and no rainfall. However, information on topography, albedo, the presence of ice, and evidence of wind speed and direction, combined with latitude, have enabled the production of a reasonably detailed climate map of the Martian surface.
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