Welcome to todayeth's Moment of Science. I do beseech thee to give ear as I tell the tale of the terrible El Niño. Okay, so my old English isn't what it should be. But if you were surprised to hear the term "El Niño" at the end of all that, you've just stumbled across a good science question.
Everybody is familiar with El Niño these days--it's those unusually warm ocean conditions along South America that can seriously change the climate. So how come you only hear about it in our lifetimes? Where was El Niño in the Middle Ages?
One study has the answer. Geologist Geoffrey Seltzer at Syracuse University and his team pulled up cores of mud from a lake in the Andes to see what the climate was like in the past. During an El Niño year a lot of silt is washed down by the rains. This silt collects on the bottom of lakes, so that by looking at the layers of silt you can tell what things were like long ago.
What did they find? There was good old El Niño, popping up again and again. The strange part was that it didn't always come at the same frequency. Between twelve thousand and seven thousand years ago there were about five El Niños per century. Their frequency increased until the ninth century when they came about once every three years.
What was speeding up El Niño's return? It isn't known, yet. But understanding more about these changes in climate is at the top of the list...for people of this century.