Why is the specific heat of water important to our planet?

Because heat keeps us warm and water hydrates the planet i guess?

Specific Heat is a property of water. If we didn't have it, our oceans would evaporate and dry up. Smaller bodies of water (lakes, ponds, rivers, streams, etc.) evaporate because they don't need as much energy to convert into water vapor. Bigger bodies of water (oceans, seas, etc) need more energy to evaporate than lakes, rivers, and etc.