Better think real hard about what you write on your next Facebook status update. Your selfie could be the butterfly wing that starts the tsunami. Evidence from a University of California, San Diego, Yale University and Facebook Inc. reported Wednesday your status can effect the mood–positively or negatively–of others.

First, the researchers found that a rainy day directly influenced the emotional tenor of a person’s Facebook posts. The effect was small but significant—the number of negative posts rose 1.16%, while the number of positive comments fell 1.19%.

That, in turn, affected the Facebook status of one or two friends in other cities where it wasn’t raining. Each additional positive post resulted in a further 1.75 positive posts among friends; while each negative post yielded 1.29 more negative posts by friends, the researchers said.

Posts were sorted by whether they contained positive or negative language, such as the word “sad” or “happy.” To strip out the effect of topic contagion, the researchers removed any status updates that were actually about the weather. “We wanted posts where it is raining on you and it is making you write negative posts that are not about the weather,” Dr. Fowler said.

With about 1.2 billion active users, a volatile upbeat or downbeat mood could quickly spread through Facebook, Dr. Fowler said. “It is going to have implications for financial markets, which have bubbles and busts, and it has implications for political activity,” he said. [SOURCE]

Imagine. Changing the world one status update plus a smily face at a time.