It definitely is one of the factors.
I live about 10-15 miles from the bay at sea level but I often visit a city only 1 mile from the water. One effect in summer is that as the land it heats up and the warm air rises, cool air from the bay is pulled inland to take its place Coolng down the city noticibly often its 10 degrees cooler their than my city. If you go to the bay shore a good breeze builds up as it gets hotter.
Well, if this is what you mean. Global warming as you probably already know is melting the ice in the arctic and more water goes into the ocean. Making beaches disappear.
Almost always, as seas warm up and cool down slowly, so nearby land gets moderated in terms of its temperature, ie not so warm in summer and not so cold in winter, also of course more chance of precipitation due increased water vapor.
How does proximity to the coast effect climate?
