Surface Water & Global Temperatures (Page 90)

Why would San Francisco--compared with Norfolk, Virginia--have warmer winters and cooler summer even though both of the cities are located at the same latitude?

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The temperatures of water and land, and their abilities to hold and release energy from the sun, are very different.
Water can absorb a lot of heat energy from the sun with little change in temperature, whereas land is just the opposite (absorbs heat energy relatively quickly, and releases heat energy relatively quickly).
Wind tends to travel from West to East at the latitudes of SF and Norfolk. The wind that flows through SF tends to be warmer in the winter and cooler in the summer, thus allowing the two cities to have different types of climates during winter and summer.
This is phenomenon is known as thermal inertia.

Temperatures on earth are moderated in different ways. Sea ice for example is a temperature moderator. Ice is more effective at moderating temperatures than certain rocks like granite. Ocean currents are waters that carry and hold much heat energy from the sun.

Waters from the equator flows towards the poles, which allows the oceans near the poles to remain ice free.

More powerful than ocean currents are heat transfers that occur via water vapor in the atmosphere. This movement of water vapor in the atmosphere travels to different places across the earth and moves heat around to help moderate the temperatures on the planet.

Without moderate temperatures, the earth would be too cold or too hot for life to exist as we know it.