From AMS Glossary
An elementary generalization of the earth's climatic pattern, based entirely upon the annual cycle of the sun's inclination.
This early climatic classification recognized three basic latitudinal zones (summerless, intermediate, and winterless), which are now known as the Frigid, Temperate, and Torrid Zones, and which are bounded by the Arctic and Antarctic Circles and the Tropic of Cancer and Tropic of Capricorn. What we now call "mathematical climate" probably corresponds to what was classically considered to be climate (from the Greek word klima, meaning "inclination"). It is sometimes used synonymously with solar climate, but the latter has a more specific theoretical connotation.