Toward more robust net primary production projections in the North Atlantic Ocean

International audiencePhytoplankton plays a crucial role in both climate regulation and marine biodiversity, yet it faces escalating threats due to climate change. Understanding future changes in phytoplankton biomass and productivity under climate change requires the utilization of Earth system models capable of resolving marine biogeochemistry. These models often differ significantly from one another, and most studies typically use the average response across an ensemble of models as the most reliable projection. However, in the North Atlantic, this straightforward method falls short of providing robust projections of phytoplankton net primary production (NPP) over the 21st century. A new inter-comparison approach was therefore developed and applied to eight models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6) exhibiting substantial divergence in their NPP projections in the North Atlantic. The basin was first divided into three bioregions tailored to the characteristics of each model using a novel method based on a clustering procedure. The mechanisms controlling NPP projections were then identified in each model and in each bioregion, revealing two mechanisms responsible for a large part of model divergence: diazotrophy in the subtropical region and the presence of an ammonium pool in the subpolar region. This allowed for an informed selection of models in each region based on the way they represent these two mechanisms, resulting in reduced projection uncertainty, enhanced total NPP decrease in the subtropical region, and a strengthened increase in small phytoplankton NPP in the subpolar North Atlantic. These model selections enhanced the decreases in carbon export and phytoplankton biomass but had no impact on zooplankton biomass. This innovative approach has strong synergies with other widely used inter-comparison techniques, such as emergent constraints, and their combination would provide valuable insights into the future trajectory of the Earth's climate syste

Daniel WALDENSTRÖM Richer and More Equal : A New History of Wealth in the West Cambridge, Polity, 2024, 256 pages (Note de lecture)

Note de lecture sur l'ouvrage de Daniel WALDENSTRÖM Richer and More Equal : A New History of Wealth in the West Cambridge, Polity, 2024, 256 page

A comparison of eight weakly dispersive Boussinesq-type models for non-breaking long-wave propagation in variable water depth

International audienceWeakly dispersive Boussinesq-type models are extensively used to model long-wave propagation in coastal areas and their interaction with coastal infrastructures. Many equations falling in this category have been formulated during the last decades, but few detailed comparisons between them can be found in the literature. In this work, we investigate theoretically and with computational experiments eight variants of the most popular models used by the coastal engineering community. Both weakly nonlinear and fully nonlinear models are considered, hoping to understand better when the additional complexity of the latter class of models is necessary or justified. We provide an overview and discuss the properties of these models, including the linear dispersion relation in uniform water depth, the second-order nonlinear coupling coefficient, the shoaling gradient, and the sensitivity to wave trough instabilities. The models are then numerically discretised using the same general strategy in a single numerical code, using fourth-order methods for time and space discretisation. Their capacity to simulate coastal wave propagation and their transformation when approaching the shore is assessed on three challenging one-dimensional benchmarks. It appears that fully nonlinear models are more consistent than their weakly nonlinear counterparts, which can occasionally perform better but show different behaviours depending on the case.</div

A Lagrangian perspective reveals the carbon and oxygen budget of an oceanic eddy

International audienc

The Old Folks at Home: Parental Retirement and Adult Children'sWell-being

We here use UK data and exploit the State Pension eligibility age to establish the causal effect of parental retirement on adult children's well-being in a Fuzzy Regression Discontinuity Design analysis. Maternal retirement increases adult children's life and income satisfaction by 0.20 standard deviations in the short run. These impacts are stronger for adult children with lower incomes, with young children of their own, and who live close to their retired parents. We emphasise the critical role of intergenerational time transfers from retired mothers in enhancing their adult children's well-being

Financement local pour le climat global? Impact d'un programme d'efficacité énergétique local sur la consommation d'énergie et la création d'emplois

Subsidy programs for home energy retrofits are a popular tool to reduce CO2 emissions. Should they be implemented at the national level to leverage economies of scale or at the local level to more finely identify the best opportunities? To examine this question, we evaluate a program introduced in the French department of Essonne and compare its performance to that of its national counterparts. In a difference-in-differences framework, we identify a 8% reduction in residential natural gas use induced by the program, implying a carbon abatement cost of €44/tCO2eq. In a triple-difference framework, we further identify a 27% increase in employment in the renovation sector in Essonne, as opposed to non-renovation sectors and neighboring departments, implying about 20 jobs created per million euro spent. Looking more carefully at contractors' origin, we find that households were more likely to hire an Essonian firm than an equally distant one based outside Essonne. Altogether, our results suggest that local programs perform better than their national counterparts, and that a fair share of their benefits are retained locally. This calls for a stronger involvement of local authorities in managing home renovation policies

Dynamic assignment without money: Optimality of spot mechanisms

International audienceWe study a large market model of dynamic matching with no monetary transfers and a continuum of agents who have to be assigned items at each date. When the social planner can only elicit ordinal agents' preferences, we prove that under a mild regularity assumption, incentive compatible and ordinally efficient allocation rules coincide with spot mechanisms. The latter specify “virtual prices” for items at each date and, for each agent, randomly select a budget of virtual money at the beginning of time. When the social planner can elicit cardinal preferences, we prove that under a similar regularity assumption, incentive compatible and Pareto efficient mechanisms coincide with spot menu of random budgets mechanisms. These are similar to spot mechanisms except that, at the beginning of time, each agent chooses within a menu, a distribution over budget of virtual money

The price of youth: Income and Age-Hypergamy

This paper focuses on the role of age gaps and income in the mating process. We test the predictions of different theories of age heterogamy using a French exhaustive administrative database of newly formed same-sex and heterosexual couples. In both heterosexual and man-man couple formation, the age gap between the richer and poorer partner, and the likelihood of an extreme age gap, increase with the income of the male richer partner, especially when he belongs to the top income decile. By contrast, women, even when they rank high in the income distribution, are usually matched with an older partner. Women are found to mate with a younger partner in only one specific case: above their 60s, when they provide at least 75% of the household income or rank higher than their partner in the distribution of income in their respective age group. The marriage market thus seems to be best described by exchange theory, mitigated by a remnant of traditional norms. In a way, the price of youth depends on the sex of the buyer

Bubbles and Crashes with Partially Sophisticated Investors

National audienceWe analyze bubbles and crashes in a model in which some investors are partially sophisticated. While the expectations of such investors are endogenously determined in equilibrium, these are based on a coarse understanding of the market dynamics. We highlight how such investors may endogenously switch from euphoria to panic and how this may lead to equilibrium bubbles and crashes even in a purely speculative market in which information is complete and it is commonly understood that the bubble cannot grow forever. We also show how this setting can match stylized empirical facts, and we investigate whether bubbles may last longer when the share of fully rational traders increases

Log-normal Mutations and their Use in Detecting Surreptitious Fake Images

International audienceIn many cases, adversarial attacks against fake detectors employ algorithms specifically crafted for automatic image classifiers. These algorithms perform well, thanks to an excellent ad hoc distribution of initial attacks. However, these attacks are easily detected due to their specific initial distribution. Consequently, we explore alternative black-box attacks inspired by generic black-box optimization tools, particularly focusing on the log-normal algorithm that we successfully extend to attack fake detectors. Moreover, we demonstrate that this attack evades detection by neural networks trained to flag classical adversarial examples. Therefore, we train more general models capable of identifying a broader spectrum of attacks, including classical black-box attacks designed for images, black-box attacks driven by classical optimization, and no-box attacks. By integrating these attack detection capabilities with fake detectors, we develop more robust and effective fake detection systems