latitude: arctic, boreal, temperate, subtropical, tropical.

humidity: humid, semi-humid, semi-arid, and arid.

seasonal variation: rainfall may be distributed evenly throughout the year, or be marked by seasonal variations.

dry summer, wet winter: most regions of the earth receive most of their rainfall during the summer months; Mediterranean climate regions receive their rainfall during the winter months.

elevation: increasing elevation causes a distribution of habitat types similar to that of increasing latitude.

Biodiversity generally increases away from the poles towards the equator, and increases with humidity.

The most widely used systems of classifying biomes correspond to latitude (or temperature zoning) and humidity.