It really depends on how quickly the climate warms. If it happens quickly enough, the thermohaline cycle of the Gulf Stream (where, in the Atlantic, the warm waters of the tropics move north to the arctic where they cool down and the current sinks to the ocean floor) can be disrupted when large amounts of ice melt, creating pools of fresh water preventing the Gulf Stream from sinking and thus stalling the Gulf Stream. Current models suggest that, should this occur, an Ice Age might be the result.

A slower warming might cause less disruption overall, though even minor changes can have significant effects on the weather. As an example, warmer waters during El Nino years, (when a specific ocean current is warmer than the ambient air temperature around it) might cause more severe raining.

I don’t know as much about cooling cycles, but again, systems are more drastically affected when change occurs rapidly rather than slowly. La Nina years occur when water currents are cooler than average, which often causes droughts in the western U.S.

Making general predictions is difficult because there are so many factors involved in the ocean hydrodynamics. Weather affects ocean currents and ocean currents affect the weather, both of which are affected by and are affecting global warming. This doesn’t take into account variations in the Earth’s orbital axis, or fluctuations in solar activity. The oceans are, in short, chaotic systems, and we can only make educated guesses, many of which may prove to be completely wrong simply because we do not have enough information.

The water cycle is largely driven by temperature, the higher the temp the faster the cycle. This is because water enters the water cycle through evapouration, primarily from the seas and oceans. As the seas and oceans become warmer less energy is required for the molecules of water to break free from being in a liquid state to being in a gaseous state. Consequently more evapouration takes place. The maximum amount of water vapour in the atmosphere is determined by Saturation Vapour Pressure (SVP), the warmer the air is the higher the SVP and the more moisture it can contain. Once SVP is reached the water vapour is expelled from the atmosphere either by deposition as dew or by condensing into water droplets which fall as precipitation. With increasing temps comes increased evapouration and therefore increased precipitation. Conversely, as temps fall there is less evapouration and less precipitation. This is one of the primary reasons for monsoons in hot climates and the very dry desert conditions in Antarctica (the snow there has accumulated very, very slowly over millions of years). Winds are the result of differences in temperatures, as temps change so too do wind patterns, winds are the delivery mechanism for precipitation. So whilst temp changes affect the rate of precipitation they also affect where it falls. There could be an average global increase or decrease in precipitation but it’s not a uniform change. For example, with the current warming we’re observing a global increase in precipitation but there are some places that are receiving less rainfall.

If the earth’s climate becomes hotter, glaciers (which hold a ton of water on the north and south poles) would begin to melt–the sea level would rise and many many places would be flooded (and eventually completely underwater). Also, sea life would die out and change due to the change in water temperature from the melting glaciers.

If the temperature got colder, the glaciers would stay, and freeze even more water, thus interuppting the water cycle in a different way.