Lewis fry Richardson Medal Lecture – How many modes are neededto predict climate bifurcations?: Lessons from an experiment

According to everyone’s experience, predicting the weather reliably over more than 8 days seems an impossible taskfor our best weather agencies. At the same time, politicians and citizens are asking scientists for climate projections severaldecades into the future to guide economic and environmental policies, especially regarding the maximum admissible emissions of CO2. To what extent is this request scientifically admissible? In this lecture we will investigate this question, focusing on the topic of predictions of transitions between metastable statesof the atmospheric or oceanic circulations. Two relevant exemples are the switching between zonal and blocked atmosphericcirculation at midlatitudes and the alternance of El Niño and La Niña phases in the Pacific ocean. The main issue is whetherpresent climate models, that necessarily have a finite resolution and a smaller number of degrees of freedom than the actualterrestrial system, are able to reproduce such spontaneous or forced transitions. To do so, we will draw an analogy betweenclimate observations and results obtained in our group on a laboratory-scale, turbulent, von Kármán flow, in which spontaneoustransitions between different states of the circulation take place. We will detail the analogy, and investigate the nature of thetransitions, the number of degrees of freedom that characterizes the latter and discuss the effect of reducing the number ofdegrees of freedom in such systems. We will also discuss the role of fluctuations and their origin, and stress the importance ofdescribing very small scales to capture fluctuations of correct intensity and scale.

Correction to: Lewis Fry Richardson: His Intellectual Legacy and Influence in the Social Sciences

In the original version of the book, the following correction were incorporated: The name “Gregory D. Hess” has now been corrected to “George D. Hess” in the pages 70, 83, 98, 111 and 145. The book and the chapters have been updated with the changes.

Weather Forecasts

Chapter 4 tells the story of numerical weather forecasting from its inception to today’s supercomputing algorithms. In 1922, Lewis Fry Richardson proposed that, since the atmosphere is subject to the laws of physics, future weather can be predicted by means of algorithmic calculations. His attempt at forecasting a single day’s weather by means of manual calculations took several months. In the late 1940s, John von Neumann resurrected Richardson’s idea and launched a project to conduct the first weather forecast by computer. The world’s first operational electronic computer – ENIAC - completed a 24-hour forecast in just one day. It appeared that accurate forecasting simply required faster computers. In 1969, Edward Lorenz discovered that tiny errors in weather measurements can accumulate during numerical forecasting to produce large errors. The so-called Butterfly Effect was alleviated by the Monte Carlo simulation method invented by Stanislaw Ulam for particle physics.

Winner of the 2019 Lewis Fry Richardson Award, Jean-Paul Azam

The award committee has chosen Jean-Paul Azam as the winner of the 2019 Lewis Fry Richardson Award in particular in recognition of his contributions to the study of violent conflict and its prevention. The jury highlighted the key role of Jean-Paul Azam’s works on applying rational choice theory to understand armed conflicts, providing a consistent conceptual framework. Many of the resulting hypotheses were empirically tested, usually with the help of some co-authors to identify the most relevant causes of violent conflicts and their prevention. His work has provided important insights on diverse topics relating to civil war and terrorism.

Winner of the 2016 Lewis Fry Richardson Award, Paul Collier: Clarity and Compassion in the Study of Civil War

The award committee has chosen Paul Collier as the winner of the 2016 Lewis Fry Richardson Award in particular in recognition of his contributions to the study of civil war. His famous paper on “Greed and grievance in civil war” – published with Anke Hoeffler in 2004, but circulating in draft form since the late 1990s – has been cited over 1000 times in the Web of Science as of mid-July 2016, and has over 5000 citations in Google Scholar. The jury also highlighted the key role of Collier’s work reviving academic research on civil war in the late 1990s, the broader impact of the World Bank group led by Collier in spurring advances in the field as well as stimulating important data collection efforts, as well as his central role in popularizing insights of academic research to a broader audience.