how will the oceans’ current be affected by global warming?

Answer 1

The actual driver of ocean currents is not properly described as temperature driven but instead is what is known as thermohaline circulation. Density of water is an important factor, but the main driver of density change is evaporation of water in tropical zones as well as freezing in polar oceans (not changes in temperature as one answer here suggests). Both evaporation and freezing remove fresh water from salt water, leaving the remaining water more saline and more dense. Likewise, melting ice in polar regions adds fresh water to the ocean and makes that water less dense.

In tropical regions vast amounts of water are evaporated by solar heat. This makes that ocean water much saltier in these tropical oceans, and currents such as the Gulf Stream carry this salty water northward towards the north Atlantic where it releases large amounts of heat. Global warming would actually accelerate this process and would not necessarily reduce ocean circulation rates. On the other hand, if polar ice melts, it could create a zone of less dense water (due to mixing of fresh water and reduced salinity) that would resist the flow of salty water northward and possibly reduce the amount of water sinking into the deep Atlantic conveyer system. This shut-down of the ocean conveyer system could very well cause global cooling.

About 12,700 years ago Earth came out of the most recent ice age and began to warm. The Ocean Conveyer was disrupted by these warmer temperatures and melting polar ice caps. Within a decade average temperatures in the North Atlantic regions dropped by 5 degrees Celsius. This cold period known as the Younger Dryas (after an Arctic wildflower) last 1300 years. A similar cooling event took place about 8,200 years ago, and lasted a century. Both of these events would be catastrophic today, and were caused by "global warming."

See:
http://www.whoi.edu/page.do?pid=12455&tid=282&cid=9986

Answer 2

It will be slowed because a lot of the circulation in the ocean is driven by density. Warm water is less dense than cold. One rises, one sinks, you get circulation. Therefore the oceans will become unhealthy

Answer 3

You might also want to do a Google Scholar search on 'gondwanaland' and the 'ocean currents' before 'North and South America' seperated the 'Atlantic' from the 'Pacific'.