How geographers redraw the lines of our changing world

Countries & Cities · Published 12 October 2026 · Updated 25 October 2026 Swipe more like this →

In short: Climate is too complex for simple maps. While most people rely on the Köppen system, American geographer Glenn Thomas Trewartha introduced a vital modification in 1966. By redefining middle latitudes to better align with vegetation patterns, he sought to fix the deficiencies of earlier classification models.

Climate classification is the formalization of systems used to group geographic areas with similar environmental conditions. These systems help scientists understand the patterns between interacting climatic processes, such as temperature, precipitation, and solar radiation. However, creating an accurate scheme is daunting because climate is a multidimensional concept, and variables often change gradually across the Earth's surface.

Because temperature and precipitation tend to change slowly over distance, the boundaries between climatic regions are often drawn somewhat arbitrarily. These lines attempt to distinguish one region from another in areas of continuous, gradual change. This can result in macroclimates—major subdivisions of continents spanning hundreds to thousands of kilometers—that are not perfectly homogeneous.

The Trewartha climate classification (TCC) was first published in 1966 by Glenn Thomas Trewartha as a modification of the Köppen–Geiger system. Trewartha's approach specifically aimed to redefine middle latitudes to be closer to vegetation zoning. To illustrate, Trewartha classifies subtropical C group climates by the presence of at least 8 months where average temperatures reach 10 °C (50 °F) or above. This differs from the original Köppen system, which Trewartha sought to improve by addressing specific deficiencies in how climatic zones were identified.

While these systems provide essential frameworks, they remain limited. No two locations on Earth experience the exact same combination of physical and biological forces, meaning every climate classification is a simplification of a much more complex, abstract reality.

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