(quoted from post at 08:18:19 09/06/15) Global warming is real. Whether it's part of humans or just the earth's cycle, who knows. The threat of global warming isn't what the extremists make it out to be, though.
Basically the gradual temperature increase causes greenland's ice to melt and run off into the ocean. This affects the salinity content. Salt water weighs more than fresh water.
Big deal, right?
It doesn't seem like much, however there's something called the great conveyor belt, which relies on the salinity content of the ocean water to function. The belt is a "stream" within the ocean. Water warms up in the Indian ocean, then flows up to greenland, where it cools, and sinks, then loops back on the sea floor to the indian ocean to repeat the process.
This is what it looks like:
The result is the warm water coming up from the tropic's giving the western shores of Europe and the eastern shores of the US a more temperate climate than they would have had the belt not been there.
When fresh water melts off of greenland, it affects the weight of the water by reducing the salinity content. This means, even though the water has cooled, it's not sinking because it doesn't weigh as much. This results in an overall slowing of the belt, less warm water is brought up, and overall cooler weather in the region is a result.
The 2004 hollywood film "The Day After Tomorrow" is a dramatization of what could happen if the belt were to stop. The belt has had numerous stalls in history, the last one thought to have caused the last mini-ice age in europe in the 1400's.
But that's how warmer global temperatures cause a cooling effect.