There are many factors, from wind currents to ocean currents that effect worldwide weather. The ocean currents are interesting as they help displace heat thereby keeping the earth temperate. This is a good thing since life enjoys a temperate atmosphere and weather pattern.
The most notable and readily recognizable of these ocean currents is the Gulf Stream. Weathermen are often heard referring to the stream during hurricane season, and other seasons as well. It has an interesting effect, however, on Europe. How?
First of all what does the Gulf Stream actually do? In simple terms it transports heat from the area of the equator toward the northern polar cap, as well as warm water. The stream also affects the weather all along its route. It's been noted that many of the seaboard nor'easters snow storms during the winter spawn from off the east coast originating at the Gulf Stream.
How all this works is this. The Gulf Stream moves north as part of the overall stream known as the conveyer belt, which is driven by both surface are patters and salt density differences. A good scientific fact to look at when looking at how the Gulf Stream works is warm rises, cold sinks. As the water cools in the north close to the surface, the water the water becomes less dense in salt content and then sinks to the bottom of the stream and moves back south. As it does so the water warms up slowly in response to the warmer water around it. It becomes less dense then rises again for its return trip north. This is in part why places like Europe have such mild winters
One thing scientists are concerned about is the fact that this conveyer belt as a whole is slowing down, and has been for the last fifty or so years. If it breaks down and stops like it did once before hundreds of years ago, it would cause a drop of temperature by about five degrees Celsius. This has actually happened once before when the North American glacier melted leaving behind what we call The Great Lakes. When it happened caused Europe to fall into a hundred year ice age. Scientists now know that part of the reason this happened is because the Gulf Stream, as well as the whole north Atlantic conveyer belt suddenly shut down when the salinity of the water dropped when the melt water off the North American glacier melted and broke the banks separating it from the north Atlantic sea. Because of the rapid desalinization of the ocean water the conveyer belt shut down. Once that happened, it disrupted the climate patterns and threw Europe into that before mentioned Ice Age.
This is one of the bad side effects of global warming. As the earth heats up more and more, though seemingly marginally, it ends up causing the land ice to melt, and scientists have noticed this happening more and more every year. A sad consequence to an avoidable problem.