Lorenz once said, "A butterfly in Brazil shakes its wings a few times, and the climate in Florence will change in three months." What does that mean? Please enlighten me!

The Butterfly Effect

The butterfly effect was put forward by meteorologist Lorenz 1963.

A butterfly flapping its wings occasionally in the tropical rain forest of Amazon basin in South America may cause a tornado in Texas within two weeks. The reason is that the movement of butterfly wings leads to the change of the surrounding air system, producing weak airflow, which in turn will cause the corresponding change of the surrounding air or other systems, causing a chain reaction, which will eventually lead to great changes in other systems.