Here's why:

* Moderates temperature: Water's high heat capacity means it can absorb large amounts of heat without significantly changing its own temperature. This helps to moderate temperatures, preventing extreme fluctuations, especially near large bodies of water.

* Stabilizes climate: The oceans, which cover 71% of the Earth's surface, act as massive heat reservoirs. They absorb heat during the summer, preventing extreme warming, and release heat during the winter, preventing extreme cooling. This helps to create a more stable climate globally.

* Influences weather patterns: Water vapor in the atmosphere acts as a powerful greenhouse gas, trapping heat and influencing weather patterns. The movement of water, through evaporation, condensation, and precipitation, is a crucial part of the Earth's climate system.

While other properties like its density and surface tension also play roles, the high heat capacity of water is the most critical factor in shaping our planet's climate.