What phenomenon is characterized by an unusually warm ocean current that impacts global weather patterns?

El Niño is a climate phenomenon that results from the warming of ocean surface temperatures in the central and eastern tropical Pacific Ocean. This unusual warming significantly impacts global weather patterns by altering atmospheric circulation. During El Niño events, areas that typically experience dry conditions may see increased rainfall, while other regions can suffer from drought. These shifts in rainfall and temperature can have far-reaching effects on agriculture, fisheries, and overall climate.

In contrast, La Niña is characterized by cooler ocean temperatures in the same regions and typically has the opposite effects on weather patterns. Hurricanes and tsunamis are distinct oceanic events but do not directly alter global weather patterns in the way that El Niño does. Hurricanes are storm systems that can occur normally in warmer ocean conditions, but they do not have the widespread, long-term climatic impacts that characterize El Niño. Tsunamis are sudden and destructive waves caused by underwater earthquakes, not a phenomenon that affects global climate patterns. Thus, the defining characteristics of El Niño make it the correct answer in this context.