How does the heat capacity of seawater affect Earth’s climate?

Water possesses an exceptionally high heat capacity, meaning it requires a significant amount of energy to change its temperature compared to other common materials like land. This property allows the world’s oceans to function as a massive thermal buffer for Earth’s climate.123

By absorbing and storing vast quantities of heat from the atmosphere, the oceans resist rapid temperature fluctuations. This heat is mixed downward during summer and upward during winter, which significantly reduces the annual range of sea surface temperatures and moderates the climate of adjacent landmasses. In the Southern Hemisphere, where there is less land, the oceans play a particularly critical role in controlling air temperatures and stabilizing the climate of the temperate zone.321

Furthermore, the ocean acts as a reservoir for heat energy trapped by greenhouse gas emissions, absorbing more than 90 percent of this excess heat since the 1970s. This capacity to store and redistribute thermal energy through ocean currents is fundamental to regulating global weather patterns and maintaining the stability of Earth's climate system.43