Importance of sea ice for the global climate:
Sea ice is a key component of the Earth’s climate system. Its importance derives primarily from its impact on the large-scale atmospheric and oceanic circulation. Sea ice influences the large-scale atmospheric circulation as it crucially affects the heat and moisture input at the lower boundary of the atmosphere.
For example, under cold winter conditions, sea ice can reduce the heat input into the atmosphere from the several hundred W/m2 that would occur over open water to just a few W/m2. In addition, sea ice contributes to so-called polar amplification, which describes the fact that climate changes are most pronounced in high latitudes.
This amplification reduces in a warming climate the poleward temperature gradient, which again can have measurable consequences for the large-scale atmospheric circulation. Sea ice also affects large-scale ocean circulation, primarily through its release of salty brine into the underlying ocean.
In particular in the Southern Ocean, this brine release is crucial for the formation of cold, dense bottom water that flows northward to fill much of the deep basins of the world’s oceans.