This situation can only be possible if energy is continuously transported from equatorial and tropical areas into middle and high latitudes. As a generalization, land heats and cools faster than water, and to a greater degree. Water has a higher specific heat than land. Specific heat - amount of energy needed to raise of 1 g of substance by 1 C. Water is a much better transmitter than land. Water bodies have unlimited supply of water for evaporation.
Evaporation cools the surface of a water body.
Because of these properties, water acts as a reservoir of heat. Just like insolation and net radiation, temperature is generally distributed by latitude. The closer to water, the lower the range. The lowest - in the tropical oceans.