The majority of Russia falls within the humid cold climate region. In the Köppen-Geiger classification scheme, this is signified by the letter .

Explanation:

Köppen-Geiger classification scheme of climate classification was developed by  Wladimir Köppen. He was a famous botanist-climatologist who classified the climatic boundaries of the world into five types namely A,B,C,D and E based on territorial vegetation.

Here, since majority of Russia falls within the humid cold climate region, in the Köppen-Geiger classification scheme, this is signified by the letter D. This type of climatic conditions has temperature greater than or equal to 10 °C during its hottest month, and temperature of –3 °C or lower during its most chilling month.

The D type of climate classification also includes certain climatic conditions like f which means no dry season, w which means winter dry, or s which means summer dry.