An Ice Age brought on by global warming was the scenario depicted in the movie THE DAY AFTER TOMORROW. While the science on which the movie based has been called into question, there may be some merit in the theory that global warming could cause an Ice Age.
Why is Europe's climate comparitively milder than other places at the same latitude? Alaska and Greenland, both the same distance to the North Pole as Europe, are covered with ice and permafrost while most of Europe is not.
The ocean currents called the Gulf Stream bring warm waters up to Europe from the Caribbean. This water brings warmth to the countries in its path. Cooler water from Europe feeds back into the loop and causes the water to flow back to the Caribbean in a continuous cycle.
The Gulf Stream has been significantly weakened in every major cooling event, including the last great Ice Age. In the past this weakening has been brought on by natural events. In current times, global warming brought on by human activities could be the cause of slowing or even stopping the Gulf Stream. If this were to happen, the cold waters would stay in the area of Europe and the Northeastern US and could mean an Ice Age for those regions.
If an Ice Age occurs, it will likely be due to the melting of polar ice. This will dump large quantities of cold, fresh water into the ocean. It would disrupt the Gulf Stream and cause the cooling of many areas that now have milder climates. The return flow of cold water from Greenland, which goes back to the Caribbean, has already showed a weakening over the last 50 years. There has been a twenty percent decline in the amount of current flowing in this direction. It stands to reason that the warm waters returning from the Caribbean have also decreased in volume. The change would not be gradual. This is a phenomenon that takes place rather quickly. Perhaps it does not happen as fast as depicted in THE DAY AFTER TOMORROW. However, it could happen within a few short years.
A slowing or stoppage of the Gulf Stream would affect the entire earth. Observations have been made of current data and historical information gleaned by studying the ocean and the lands around it. With all the information at hand, it appears that it is indeed possible that global warming could bring about a modern Ice Age.