## TL;DR
Earth's surface is divided into distinct climate zones and biomes with characteristic temperature, precipitation, and vegetation patterns. These zones are shifting poleward at unprecedented rates due to anthropogenic climate change.

## Core Explanation
The Koppen system uses three-letter codes (e.g., Cfa = humid subtropical). The latitudinal climate gradient is modified by altitude (environmental lapse rate: ~6.5 C/km), ocean currents, and continentality.

## Detailed Analysis
Climate change shifts biome boundaries: boreal forests advance into tundra (Arctic greening), deserts expand into semi-arid zones, tropical species migrate upslope. The treeline advances uphill at ~5-10m/decade.

## Further Reading
- IPCC Sixth Assessment Report: Biomes
- World Wildlife Fund: Terrestrial Ecoregions
- Nature Climate Change