The North Atlantic current carries warmer water from the south toward the Arctic and back again. Climates in the Northern Hemisphere rely on this circulation to keep winter temperatures in check and assist in the changing of the seasons. But as the Earth warms and glaciers melt, more freshwater is being dumped into the Atlantic. This influx of warmer freshwater has the potential to trigger massive changes in the current's behavior, such as shutting it off completely or creating longer circulation times. In both of these circumstances, winters would become longer and more severe.
The freshwater flowing into the Atlantic is decreasing the amount salt in the water. This change in the salinity of the water has the potential to change the behavior of the currents. This is because water with less salt is less dense. Water that is less dense will remain closer to the surface and move at a different pace than dense salt water. So, this density shift will alter the movement of currents that force cooler, deeper water south and warmer, surface water north.
Glacial runoff and increased precipitation cause the Atlantic ocean water levels to rise. This increase will affect human populations living in coastal areas, forcing these communities to relocate as beaches and islands disappear. This change will affect the east coasts of North and South America, and the west coasts of Europe and Africa. It will also have a direct impact on islands in the Atlantic Ocean.
Hotter temperatures and long sun exposure create an ideal environment for the propagation of certain ecosystems, such as algae. The increase on algae has the potential to block life-giving sun rays for other organisms, putting shallow water ecosystems at risk. Algae blooms appear in the North Atlantic every year, but warming climates may cause more algae blooms to appear earlier and stick around longer.
According to a study conducted by Thomas R. Knutson, of the Geophysical Fluid Dynamics Laboratory, global warming may, over time, have a direct effect on the frequency and strength of hurricanes over the Atlantic Ocean. The study, however, finds that no conclusive evidence points to a relationship between increased hurricane activity and global warming. Knutson theorizes that the relationship is possible, but because hurricanes are dependent on so many factors, it is hasty to assume their increase is due to human activity.