WASHINGTON — Edward Lorenz, the father of chaos theory, died at his home in Cambridge, Mass., Wednesday. He was 90.

He was a professor at the Massachusetts Institute of Technology when he came up with the scientific concept that small effects lead to big changes, something that became known as the "butterfly effect." He explained how something as minuscule as a butterfly flapping its wings in Brazil changes the constantly moving atmosphere in ways that could later trigger tornadoes in Texas.

His discovery of "deterministic chaos" brought about "one of the most dramatic changes in mankind's view of nature since Sir Isaac Newton," said the committee that awarded Lorenz the 1991 Kyoto Prize for basic sciences. It was one of many scientific awards that Lorenz won. There is no Nobel Prize for his specific field of expertise, meteorology.

Jerry Mahlman, a longtime friend, noted that the man who pioneered chaos theory was "the most organized person I ever knew."

Lorenz came up with the chaos theory concept in the 1960s through his own meticulous work habits, said Kevin Trenberth, a student of Lorenz's. Trenberth is now climate analysis chief at the National Center for Atmospheric Research.

He inadvertently ran what seemed like the same calculations through a creaky computer twice and came up with vastly different answers. When he tried to figure out what happened, he noticed a slight decimal point change — less than 0.0001 — wound up leading to significant error. That error became a seminal scientific paper, presented in 1972, about the butterfly effect.

Lorenz was "the quiet geek" who turned the old concept of "wiggle room" into hard numbers and scientific theory, said Mahlman, a retired federal climate scientist. Meteorologists today base their forecasts on his techniques. Lorenz's 1967 book "The Nature and Theory of the General Circulation of the Atmosphere" is considered a classic textbook in meteorology.

The concept of small changes turning into big effects also influenced many basic sciences. Other fields probably benefited more than meteorology, said MIT meteorology professor Alan Plumb.

Lorenz also was incredibly quiet. Getting him to talk was painfully difficult, his colleagues said, except around his late wife, Jane. He rarely wrote papers with others.

"Of all the geniuses of that era, he was the quietest and most humble and the most kind," said Mahlman.

Lorenz was born in West Hartford, Conn., in 1917 and later wrote in a biographical sketch: "As a boy I was always interested in doing things with numbers and was also fascinated by changes in the weather."

He had degrees from Dartmouth College and Harvard University as well as MIT where he joined the meteorology staff in 1948. He later became department head and retired in 1987.

In 1983, with a colleague, he won the $50,000 Crafoord Prize by the Royal Swedish Academy of Sciences, which recognizes leaders in scientific fields not eligible for a Nobel.

Lorenz was an avid hiker and climber, who well into his 80s would "put many younger people to shame in terms of his fitness and love of going into the mountains," Trenberth said.

Lorenz is survived by three children.