An increase in global temperatures and precipitation could add a lot more freshwater to the North Atlantic as glacial meltwater flows into the ocean. Similar to events after the last ice age (10,000 years) this could again stop the Gulf Stream and drop temperatures in Europe by around 5 degrees C.
El Niño and climate change
El Niño events have in recent years increased in frequency and are often not interrupted by La Niña events (the opposite of this particular climatic seesaw).
A number of scientists say that these changes cannot be explained by natural causes. While scientific consensus is still out, Climate Witnesses in Fiji or in the Sunderbans are already reporting changes in their daily lives.