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American mathematician (1917 – 2008)

Edward Norton Lorenz (May 23, 1917 – April 16, 2008) was an American mathematician and meteorologist who established the theoretical basis of weather and climate predictability, as well as the basis for computer aided atmospheric physics and meteorology. He is best known as the founder of modern chaos theory, a branch of mathematics focusing on the behavior of dynamical systems that are highly sensitive to initial conditions. His discovery of deterministic chaos "profoundly influenced a wide range of basic sciences and brought about one of the most dramatic changes in mankind's view of nature since Sir Isaac Newton," according to the committee that awarded him the 1991 Kyoto Prize for basic sciences in the field of earth and planetary sciences.

Lorenz was born in 1917 in West Hartford, Connecticut. He acquired an early love of science from both sides of his family. His father, Edward Henry Lorenz (1882 1956), majored in mechanical engineering at the Massachusetts Institute of Technology, and his maternal grandfather, Lewis M. Norton, developed the first course in chemical engineering at MIT in 1888. Meanwhile, his mother, Grace Peloubet Norton (1887 1943), instilled in Lorenz a deep interest in games, particularly chess. Later in life, Lorenz lived in Cambridge, Massachusetts with his wife, Jane Loban, and their three children, Nancy, Cheryl, and Edward. He was an avid outdoorsman, who enjoyed hiking, climbing, and cross country skiing. He kept up with these pursuits until very late in his life. On April 16, 2008, Lorenz died at his home in Cambridge from cancer at the age of 90.

Lorenz received a bachelor's degree in mathematics from Dartmouth College in 1938 and a master's degree in mathematics from Harvard in 1940. He worked as a weather forecaster for the United States Army Air Forces during World War II, leading him to pursue graduate studies in meteorology at the Massachusetts Institute of Technology.

Lorenz spent the entirety of his scientific career at the Massachusetts Institute of Technology. In 1948, he joined the MIT Department of Meteorology as a research scientist. In 1955, he became an assistant professor in the department and was promoted to professor in 1962. From 1977 to 1981, Lorenz served as head of the Department of Meteorology at MIT. In 1983, the MIT Department of Meteorology and Physical Oceanography merged with the Department of Geology to become the current MIT Department of Earth, Atmospheric and Planetary Sciences, where Lorenz remained a professor before becoming an emeritus professor in 1987.

In the late 1940s and early 1950s, Lorenz worked with Victor Starr on the General Circulation Project at MIT to understand the role the weather system played in determining the energetics of the general circulation of the atmosphere. From this work, in 1967, Lorenz published a landmark paper, titled "The Nature and Theory of the General Circulation of the Atmosphere," on atmospheric circulation from an energetic perspective, which advanced the concept of available potential energy.

In the 1950s, Lorenz became interested in and started work on numerical weather prediction, which relied on computers to forecast weather by processing observational data on such things as temperature, pressure, and wind. This interest was sparked, in part, after a visit to the Institute for Advanced Study in Princeton, New Jersey, where he met Jule Charney, then head of the IAS's Meteorological Research Group and a leading dynamical meteorologist at the time. (Charney would later join Lorenz at MIT in 1957 as a professor of meteorology.) In 1953, Lorenz took over leadership of a project at MIT that ran complex simulations of weather models that he used to evaluate statistical forecasting techniques.

In 1961, Lorenz was using a simple digital computer, a Royal McBee LGP 30, to simulate weather patterns by modeling 12 variables, representing things like temperature and wind speed. He wanted to see a sequence of data again, and to save time he started the simulation in the middle of its course. He did this by entering a printout of the data that corresponded to conditions in the middle of the original simulation. To his surprise, the weather that the machine began to predict was completely different from the previous calculation. The culprit: a rounded decimal number on the computer printout. The computer worked with 6 digit precision, but the printout rounded variables off to a 3 digit number, so a value like 0.506127 printed as 0.506. This difference is tiny, and the consensus at the time would have been that it should have no practical effect. However, Lorenz discovered that small changes in initial conditions produced large changes in long term results. Lorenz's discovery, which gave its name to Lorenz attractors, showed that even detailed atmospheric modelling cannot, in general, make precise long term weather predictions. His work on the topic, assisted by Ellen Fetter, culminated in the publication of his 1963 paper "Deterministic Nonperiodic Flow" in Journal of the Atmospheric Sciences, and with it, the foundation of chaos theory. In the book "The Essence of Chaos," in the chapter "Our Chaotic Weather" from 1993, authored by Edward Lorenz and Krzysztof Haman, the authors delved into the challenges of weather forecasting. The work discusses the consequences of chaos in the atmosphere and its impact on weather prediction. They describe a scenario in which meteorologists, in the computer age, generate multiple long term weather forecasts based on different yet similar initial atmospheric conditions. Differences in the forecast results arise due to the sensitivity of the system to initial conditions. Lorenz's insights on deterministic chaos resonated widely starting in the 1970s and 80s, when it spurred new fields of study in virtually every branch of science, from biology to geology to physics. In meteorology, it led to the conclusion that it may be fundamentally impossible to predict weather beyond two or three weeks with a reasonable degree of accuracy. However, the recognition of chaos has led to improvements in weather forecasting, as now forecasters recognize that measurements are imperfect and thus run many simulations starting from slightly different conditions, called ensemble forecasting. Of the seminal significance of Lorenz's work, Kerry Emanuel, a prominent meteorologist and climate scientist at MIT, has stated: the Buys Ballot Award in 2004, and the Tomassoni Award in 2008. In 2018, a short documentary was made about Lorenz's immense scientific legacy on everything from how we predict weather to our understanding of the universe.

Lorenz is remembered by colleagues and friends for his quiet demeanor, gentle humility, and love of nature.

In February 2018, The Edward Lorenz Center and Henry Houghton Fund hosted a symposium, named MIT on Chaos and Climate, in honor of the 100th anniversary of the birth of Lorenz and Charney.

Lorenz published many books and articles, a selection of which can be found below. A more complete list can be found on the Lorenz Center website: link
1955 Available potential energy and the maintenance of the general circulation. Tellus. Vol. 7; 2. Link
1963 Deterministic nonperiodic flow. Journal of the Atmospheric Sciences. Vol. 20: 130–141. Link. 1967 The nature and theory of the general circulation of atmosphere. World Meteorological Organization. Vol. 218. Link
1969 Three approaches to atmospheric predictability. Bulletin of the American Meteorological Society. Vol. 50; 345–349. Link
1972 Predictability: Does the Flap of a Butterfly's Wings in Brazil Set Off a Tornado in Texas? American Association for the Advancement of Sciences; 139th meeting. Link
1976 Nondeterministic theories of climate change. Quaternary Research. Vol. 6. Link
1990 Can chaos and intransitivity lead to interannual variability? Tellus. Vol. 42A. Link
2005 Designing Chaotic Models. Journal of the Atmospheric Sciences. Vol. 62, No. 5: 1574–1587. Link