Nonlinear Processes in Geosciences

Nonlinear Processes in Geosciences

Abrupt Warming could bring our planet a “Hothouse Earth” with catastrophic consequences for our economy and society

Abrupt Warming could bring our planet a “Hothouse Earth” with catastrophic consequences for our economy and society

Most of us have enjoyed swings in childhood. Some have even tried to swing faster and make a full 360 degrees’ loop. Those who succeeded had a very strange feeling of not being able to predict whether, increasing the energy of the swing, the transition from normal oscillations and 360 loops would happen. Indeed, there is an energy threshold such that the swing goes from oscillations to full loops and the change in the behavior is abrupt. Say now that the swing is our planet and the energy pumped in the Earth system are the anthropogenic emissions, in a recently published paper in the Proceedings of the National Academy of Sciences ( Will Steffen and co-authors found that increasing the emissions would push the earth towards an abrupt change in trajectory, leading in a very short time span to a 5 degrees’ warmer climate.

Up to now, scientists have predicted a fast but smooth increase of the planet temperature with increasing anthropogenic emissions. Although catastrophic, this scenario would leave enough time to adapt our society to a warmer climate and the associated consequences such as sea-level rise. This study has however identified a series of interconnected factors which could cause a chain reaction and push the Earth towards a “hothouse” state. Deforestation, permafrost thawing, relative weakening of land and ocean physiological CO2 sinks can drive further warming – even if we stop emitting greenhouse gases. Like going through the full loop could cause injuries, this process is likely to be unstoppable and irreversible and will lead to devastating consequences. The authors say: “a Hothouse Earth trajectory will likely exceed the limits of adaptation and result in a substantial overall decrease in agricultural production, increased prices, and even more disparity between wealthy and poor countries”. A Hothouse Earth trajectory would almost certainly flood deltaic environments, increase the risk of damage from coastal storms, and eliminate coral reefs (and all of the benefits that they provide for societies) by the end of this century or earlier.

The results of this study have animated a debate in the climate change community and there is actually a substantial disagreement about the possibility of crossing the tipping point described in the article. The non-linear geophysics community is working hard to understand these critical phenomena in simple systems which represents idealized climate.

Workshop report: Mathematics of the Economy and Climate

Workshop report: Mathematics of the Economy and Climate

Just before the summer a group of about 40 scientists gathered in an old Monastery in the Netherlands (Kontakt der Kontinenten, Soesterberg) for a rather special collaborative workshop entitled “Mathematics of the economy and climate”. Mathematicians, climate scientists and economists – a group of scientists that normally does not mix and are rather unfamiliar with each other’s research – joined together for three days to learn from each other and discuss the most pressing research questions around ongoing climate change and its connections with the development of economic systems (

The workshop included high-profile speakers from Imperial College, ENS Lyon, London School of Economics and Yale. Prof. Tony Smith from Yale reported on recent research using the integrated assessment model developed by his colleague William Nordhaus (Nobel prize 2018) and presented attempts to view the global economic system and its interaction with climate in a spatially resolved way. This and many other interesting talks triggered lively discussions on, e.g., the adequacy of models in general and in particular in the different fields of research. Uncertainty in both the climate response and the economic development was one issue that was extensively discussed as it appears that economists tend to assume future climate (measured by, e.g., the equilibrium or transient climate sensitivity) as relatively well-known and vice versa.

There is still a long way to go for a good understanding of the combined evolution and interaction of the climate and the economic system. This workshop was a starting point for the different disciplines to learn to talk to each other. Participants enjoyed discussing with academics from different areas in an open-minded atmosphere. Finally it became clear that there are exciting and novel mathematical techniques available such as numerical methods for stochastic differential equations and dynamical systems to tackle the challenges ahead.

June Heatwave 2019: can we attribute the event to anthropogenic emission?

June Heatwave 2019: can we attribute the event to anthropogenic emission?

If August Rodin had lived nowadays, he would have placed his gates of hell (la Porte de l’Enfer) in Gallargues-le-Montueux, where the absolute French temperature record (45.9 °C) was set on June 28th this year.

The last week of June has been very hot, not only in the south of France, but overall central Europe: in the Alps, some locations such as Chamonix (France) and Aosta (Italy) experienced temperatures close or above 40°C, setting absolute records. The atmospheric circulation responsible for this event consisted of a marked low pressure system centered on the Atlantic Ocean between France and Spain and a high pressure ridge extending from Morocco and Algeria up to central France and the Alpine regions. The strong Meridional wind caused exceptionally warm air advection from Africa and loads of Saharan dusts.

June heatwaves can have a large impact on professional and educational activities compared to July and August heatwaves, where most of the people are on holiday. It is therefore important to understand if greenhouse emissions have affected the intensity of such event and if similar heatwaves will be more likely in the future. A branch of climate science, termed attribution, tries to provide these answers via European collaborative projects (e.g. EUPHEME). The June 2019 heatwave is very interesting from this point of view because a quick attribution study has been published, at a record time, just few days after the events.

The first step for attributing the event to climate change is to provide its definition: which variable/indicator? Which spatial area? Which period of time? In their study the authors considered the three-day average of daily mean temperatures, as they are relevant for health impacts, and two spatial scales: the whole of France and one city, Toulouse. Only June heatwaves were analyzed because the atmospheric circulation is generally different in June than in July and August and the impacts are also different.

The study used a combination of high resolution observations and state-of-the-art climate models to highlight that the probability of this event has largely increased compared to the past and that similar events will be more likely in the future. The authors found that this event is about 4°C warmer than a century ago. They have however also recognized that the quantification of the increase in probability of this event under climate change strongly depends on the models/observations considered. They pointed out to the inadequacy of current models at simulating these events. This poses serious challenges both for the scientific community as well as for the decision makers: on one side, new techniques should be developed to improve the representation of extreme events in climate models. The non-linear geophysics community strongly contributes to this task by proposing bias correction algorithms to improve models output, and techniques issued from dynamical systems theory or statistical mechanics to simulate heatwaves with large deviations. On the other side, decision makers should be aware that uncertainty is a key feature of these studies and take action to prevent the worst possible scenarios both with adaption strategies (heat plans) and by reducing greenhouse gases emissions.

NP Interviews: the Division President Stéphane Vannitsem

NP Interviews: the Division President Stéphane Vannitsem

Today’s NP Interviews hosts the Nonlinear Processes Division President Stéphane Vannitsem.

Stéphane is the head of the Dynamical Meteorology and Climatology Unit of the Research division of the Royal Meteorological Institute of Belgium, and lecturer at the Free University of Brussels. He is currently president of the Nonlinear Processes division of the European Geosciences Union and executive editor of the journal “Nonlinear Processes in Geophysics”. His main research interests and expertise are oriented toward the application and adaptation of techniques of dynamical systems theory, chaos theory and stochastic processes to the study of atmospheric and climate dynamics with emphasis on their variability and predictability.

What is the NP Division?

The Nonlinear Processes in Geosciences (NP) Division was born at the early stages of the development of the Union, at that time the European Geophysical Society (EGS), with the aim at promoting new techniques and theories on the properties and dynamics of systems displaying nonlinearities.

Why are nonlinearities important?

Nonlinearities are generic in our environment and are at the heart of the complexity of the systems geoscientists are dealing with. As these nonlinearities are affecting all fields of geosciences, the NP division is a truly interdisciplinary (even transdisciplinary) division attracting scientists working on nonlinear problems and/or at the crossroads between different disciplines.

What are these disciplines and aspects?

The main themes covered by our interdisciplinary division and the corresponding officers are listed at Aspects covered are the mathematics, the dynamics, the modelling and the statistics of nonlinear processes in all geosciences fields from the Earth interior to the outer space.

What about sessions and short courses during the General Assembly?

As an interdisciplinary division dealing with state-of-the-art and brand new techniques and with new nonlinear mechanisms, NP is of course promoting co-organization of sessions with the other divisions. At the same time, members of the division are proposing short courses in which advanced techniques are presented. These courses have a lot of success among young scientists, and are usually full and often people are standing outside the rooms. These courses are definitely a success for the NP division, allowing for more visibility of our activities and a faster diffusion of new promising approaches and new nonlinear mechanisms.

Great! Are there also some awards and medals?

On top of the usual oral and poster presentations, the NP division awards excellent young scientists by means of an outstanding Early Career Scientist (ECS) Award and for more accomplished scientists through the Lewis Fry Richardson Medal. The latter has been first awarded in 2004 and the list of awardees can be found at Lewis Fry Richardson was a pioneer in turbulence in which nonlinearities are the generic elements of the complex behavior of the fluid, and had also a strong vision on how numerical weather prediction should be made. All awardees have substantially contributed to advancing our understanding of the impact of nonlinearities throughout geosciences. The NP ECS Award was first delivered in 2011 and the list of young awardees can also be found at, illustrating how lively this field is and how young scientists are still enthusiastic by the problems to be solved from the challenging Earth System evolution to Solar Flares, or Rogue waves (without being exhaustive at all).

How large is the NP Division?

Since its start, the NP Division has grown in size until to reach an average of 300-400 abstracts per year. This size is obviously small as compared to the main divisions of the EGU that can reach several thousands of abstracts, but plays an essential role in diffusing new advanced techniques throughout the Union.

Is there a publishing journal for researchers in nonlinear processes?

The NP division members have set up in the early days of the EGS a journal “Nonlinear Processes in Geophysics”. This journal published by the EGU – and co-listed among the partner journals of the AGU – covers all aspects of nonlinear geophysics. The impact factor is not high, but the quality of papers and new ideas is. This forum is clearly a place for promoting research on nonlinear processes, and I encourage young scientists to take part of the nonlinear adventure by submitting good papers to this journal. The link to the journal is at