Edward Norton Lorenz

Atmospheric circulation

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.^[11]

Numerical weather prediction

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.^[12] (Charney would later join Lorenz at MIT in 1957 as a professor of meteorology.)^[13] 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.^[12] By the late 1950s, Lorenz was skeptical of the appropriateness of the linear statistical models in meteorology, as most atmospheric phenomena involved in weather forecasting are non-linear.^[2] It was during this time that his discovery of deterministic chaos came about.^[14]

Chaos theory

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.^[15]

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.^[2][14] He states in that paper:

"Two states differing by imperceptible amounts may eventually evolve into two considerably different states ... If, then, there is any error whatever in observing the present state—and in any real system such errors seem inevitable—an acceptable prediction of an instantaneous state in the distant future may well be impossible....In view of the inevitable inaccuracy and incompleteness of weather observations, precise very-long-range forecasting would seem to be nonexistent."

His description of the butterfly effect, the idea that small changes can have large consequences, followed in 1969.^{[2][16][17][18][19][20][21]}

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. ^[22]

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.^[23]

Of the seminal significance of Lorenz's work, Kerry Emanuel, a prominent meteorologist and climate scientist at MIT, has stated:^[8]

"By showing that certain deterministic systems have formal predictability limits, Ed put the last nail in the coffin of the Cartesian universe and fomented what some have called the third scientific revolution of the 20th century, following on the heels of relativity and quantum physics."

Late in his career, Lorenz began to be recognized with international accolades for the importance of his work on deterministic chaos. In 1983, along with colleague Henry Stommel, he was awarded the Crafoord Prize from the Swedish Academy of Sciences, considered to be nearly equal to a Nobel Prize.^[8] He was also awarded the Kyoto Prize for basic sciences in the field of earth and planetary sciences in 1991,^[24] the Buys Ballot Award in 2004, and the Tomassoni Award in 2008.^[25] 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.^[26]

The Lorenz Center

In 2011, The Lorenz Center, a climate think tank devoted to fundamental scientific inquiry, was founded at MIT in honor of Lorenz and his pioneering work on chaos theory and climate science.^[27]

Centenary celebration

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.^[13] The two-day event featured presentations from world-renowned experts on the many scientific contributions that the two pioneers made on the fields of numerical weather prediction, physical oceanography, atmospheric dynamics, and experimental fluid dynamics, as well as the personal legacy they left behind of integrity, optimism, and collaboration. A video produced for the event highlights the indelible mark made by Charney and Lorenz on MIT and the field of meteorology as a whole.^[28]