Final answer:
Glaciers advance when cold, snowy winters are followed by cool, wet summers, resulting in a buildup of ice that surpasses melting. Earth's rotational axis, elevation, and latitude influence these conditions, leading to glaciation periods during ice ages. Modern climate and biological data aids in predicting these trends.
Step-by-step explanation:
Glaciers advance under climatic conditions where winters are cold enough to produce significant snowfall, and summers are cool enough that not all of the accumulated snow and ice melt away. When cold, very snowy winters are followed by cool, wet summers, glaciers are more likely to gain mass and advance. The accumulation of ice exceeds the rate of melting, allowing glaciers to grow. Factors like the Earth's spin axis, elevation, and latitude can also influence these conditions. Colder temperatures and increased snowfall in the winter contribute to the growth of glaciers because the snow and ice do not melt entirely during the summer. This net gain in glacial ice can eventually lead to the advance of glaciers, contributing to periods known as glaciation during ice ages.
Modern climate data and observations, such as sea level changes, glacier dimensions, and biological indicators like tree rings, help scientists understand and predict climatic trends and glacial movements.