The common perception of how global warming works is that greenhouse gases are released into the atmosphere, which traps heat and leads to a rise in Earth’s temperature. The more plausible theory is that global warming would lead to the melting of the ice caps and permafrost in the more northern/southern (in the southern hemisphere) regions. The water would then drain into the oceans, which would interrupt the current streams that bring warm air from the equator and this lack of heat from the equator would lead to a cooling of the Earth.
Still following me? Good, because it seems that this theory could play out in Europe. According to researchers at the Royal Netherlands Institute of Sea Research, there is a 7,500 cubic kilometer pool of fresh water in the Arctic Ocean. This pool of fresh water could lead to a disruption of the gulf stream, which would lead to cooler temperatures in parts of Europe and North America.
Sea ice is melting quicker. It is thinner and more mobile, and could exit the Arctic faster. Also more of it will enter the Atlantic as liquid water rather than ice.
If the gulf stream were slowed, interrupted or otherwise hindered in any way, the result would be cooler year-round temperatures. The question would then become one of “how drastic,” and that question is a much harder one to answer.