Biomes Graph
To the right of the player is a Taiga (mostly over the ocean), to the left is either a Forest, or Woods, I can’t remember. In the distance is probably tundra.
According to Wikipedia,Biomes are climatically and geographically defined as similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems.
In Minecraft, hopefully from the Halloween update onwards, this means different areas, with different features based on it's height, temperature, humidity etcetera.
Before the Halloween update, when a map was generated it got a 'theme', e.g. Snowy or Grassy. After this update a single world will include all themes in a logical fashion.
Current Savegames
Worlds on current savegames will not be changed. However, any new chunks generated (by the player moving outside of the current world's bounds) will use biomes, just as Hell will be generated when you enter it first.
Biome Types
There will be 11 Biome types: (Note these names come from Notch's notes)
- Rain Forest
- Swamp
- Seasonal Forest
- Forest
- Savanna
- Woods
- Taiga
- Desert
- Grassy Desert
- Tundra
- Hell
Notch
Remaining work on biomes include letting them change the elevation (deserts, plains, tundras and swamps should all be flat), and changing the grass color depending on the biome type. The border between frozen biomes and not frozen ones will get way nicer.
The sky color changes slightly depending on how cold the area you are in is.