Evolution of the Atlantic Multidecadal Variability in a model with an improved North Atlantic Current

This article investigates the dynamics and temporal evolution of the Atlantic Multidecadal Variability (AMV) in a coupled climate model. The model contains a correction to the North Atlantic flow field to improve the path of the North Atlantic Current, thereby alleviating the surface cold bias, a common problem with climate models, and offering a unique opportunity to study the AMV in a model. Changes in greenhouse gas forcing or aerosol loading are not considered. A striking feature of our results is the contrast between the western and eastern sides of the subpolar gyre in the model. On the western side, heat supply from the ocean plays a major role, with most of this heat being given up to the atmosphere in the warm phase, largely symmetrically about the time of the AMV maximum. By contrast, on the eastern side, the ocean gains heat from the atmosphere, with relatively little role for ocean heat supply in the years before the AMV maximum. Thereafter, the balance changes with heat now being removed from the eastern side by the ocean leading to a reducing ocean heat content, behavior we associate with the establishment of an intergyre gyre at the time of the AMV maximum. In the warm phase, melting sea-ice leads to a freshening of surface waters northeast of Greenland which travel southward into the Irminger and Labrador Sea, shutting down convection and terminating the AMV warm phase

The Sun's role in decadal climate predictability in the North Atlantic

Despite several studies on decadal-scale solar influence on climate, a systematic analysis of the Sun's contribution to decadal surface climate predictability is still missing. Here, we disentangle the solar-cycle-induced climate response from internal variability and from other external forcings such as greenhouse gases. We utilize two 10-member ensemble simulations with a state-of-the-art chemistry–climate model, to date a unique dataset in chemistry–climate modeling. Using these model simulations, we quantify the potential predictability related to the solar cycle and demonstrate that the detectability of the solar influence on surface climate depends on the magnitude of the solar cycle. Further, we show that a strong solar cycle forcing organizes and synchronizes the decadal-scale component of the North Atlantic Oscillation, the dominant mode of climate variability in the North Atlantic region.publishedVersio

The role of atmospheric feedbacks in ENSO simulation and projection

El Niño/Southern Oscillation (ENSO) is the most dominant mode of climate variability on interannual time scales in the tropical Pacific sector and arises from a complex interplay between amplifying and damping feedbacks. Given its large socio-economic impacts caused by e.g. severe weather events such as floods and droughts in various regions of the world, it is very important to accurately predict how ENSO will change under global warming. Despite improvements have been made in simulating ENSO over the last decades, a realistic representation of ENSO and its projection under global warming remains a challenge. ENSO projections widely differ amongst climate models participating in the phase 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6), which are the base of the assessment reports of the Intergovernmental Panel on Climate Change (IPCC). Although these models simulate ENSO, which in terms of simple indices are consistent with observations, the underlying dynamics are very different from the observed. In observations, an initial SST anomaly grows during ENSO events by wind-induced changes in the ocean dynamics. This tendency is counteracted by damping surface heat flux feedback, especially the atmospheric shortwave radiation and latent heat flux damping. In most climate models, however, the wind- SST feedback is too weak and the shortwave-SST feedback erroneously positive so that ENSO is a hybrid of wind-driven and shortwave-driven dynamics. In the most biased models, the shortwave-SST feedback contributes to the SST anomaly growth to a similar degree as the wind-SST feedback. As the models not only underestimate the wind-SST feedback but also heat flux damping, this error compensation explains why models with less than a half of the observed wind-SST feedback strength can still exhibit realistic ENSO amplitude. A broad continuum of ENSO dynamics exists in the climate models that may explain the large spread in 21st century ENSO projections. In the IMBE21C project, the effect of biased ENSO dynamics on ENSO projections will be investigated. With a new method, based on an ‘Offline Slab Ocean SST’, we can quantify the effects of the amplifying and damping feedbacks by separating the SST changes caused by the wind-driven ocean dynamics and by atmospheric heat fluxes. In this project we will use this method to quantify the forcing and damping in observed ENSO dynamics and to compare it with the modeled ENSO to identify and quantify the biases of the simulated ENSO dynamics. Further we will analyze global warming projections with respect to the influences of biased ENSO dynamics by dividing the models into groups with realistic and biased ENSO dynamics. Overall, IMBE21C aims at identifying sources of uncertainties in ENSO projections by innovative methods and will try to reduce them

The Flexible Ocean and Climate Infrastructure Version 1 (FOCI1): Mean State and Variability

A new Earth system model, the Flexible Ocean and Climate Infrastructure (FOCI), is introduced. A first version of FOCI consists of a global high-top atmosphere (ECHAM6.3) and an ocean model (NEMO3.6) as well as sea ice (LIM2) and land surface model components (JSBACH), which are coupled through the OASIS3-MCT software package. FOCI includes a number of optional modules which can be activated depending on the scientific question of interest. In the atmosphere, interactive stratospheric chemistry can be used (ECHAM6-HAMMOZ) to study, for example, the effects of the ozone hole on the climate system. In the ocean, a biogeochemistry model (MOPS) is available to study the global carbon cycle. A unique feature of FOCI is the ability to explicitly resolve mesoscale ocean eddies in specific regions. This is realized in the ocean through nesting; first examples for the Agulhas Current and the Gulf Stream systems are described here. FOCI therefore bridges the gap between coarse-resolution climate models and global high-resolution weather prediction and ocean-only models. It allows to study the evolution of the climate system on regional and seasonal to (multi-) decadal scales. The development of FOCI resulted from a combination of the long-standing expertise in ocean and climate modeling in several research units and divisions at GEOMAR. FOCI will thus be used to complement and interpret long-term observations in the Atlantic, enhance the process understanding of the role of mesoscale oceanic eddies for large-scale oceanic and atmospheric circulation patterns, study feedback mechanisms with stratospheric processes, estimate future ocean acidification, improve the simulation of the Atlantic Meridional Overturning Circulation changes and their influence on climate, ocean chemistry and biology. In this paper we present both the scientific vision for the development of FOCI as well as some technical details. This includes a first validation of the different model components using several configurations of FOCI. Results show that the model in its basic configuration runs stably under pre-industrial control as well as under historical forcing, and produces a mean climate and variability which compares well with observations, reanalysis products and other climate models. The nested configurations reduce some long-standing biases in climate models and are an important step forward to include the atmospheric response in multi-decadal eddy-rich configurations

Biocultural approaches to sustainability : A systematic review of the scientific literature

Current sustainability challenges demand approaches that acknowledge a plurality of human-nature interactions and worldviews, for which biocultural approaches are considered appropriate and timely. This systematic review analyses the application of biocultural approaches to sustainability in scientific journal articles published between 1990 and 2018 through a mixed methods approach combining qualitative content analysis and quantitative multivariate methods. The study identifies seven distinct biocultural lenses, that is, different ways of understanding and applying biocultural approaches, which to different degrees consider the key aspects of sustainability science-inter- and transdisciplinarity, social justice and normativity. The review suggests that biocultural approaches in sustainability science need to move from describing how nature and culture are co-produced to co-producing knowledge for sustainability solutions, and in so doing, better account for questions of power, gender and transformations, which has been largely neglected thus far. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.Peer reviewe

Atlantic Multidecadal Variability in a model with an improved North Atlantic Current

We examine the simulated Atlantic Multidecadal Variability (AMV) in a model that includes a correction for a longstanding problem with climate models, namely the misplacement of the North Atlantic Current. The corrected model shows that in the warm AMV phase, heat is lost by the ocean in the northwestern part of the basin and gained by the ocean to the east, suggesting an advective transfer of heat by the mid-latitude westerlies. The basin wide response is consistent with a role for cloud feedback and is in broad agreement with estimates from observations, but is poorly represented in the uncorrected model. The corrected model is then used to show that the ocean/atmosphere heat transfer is influenced by low frequency variability in the overlying atmosphere. We also argue that changing ocean heat transport is an essential feature of our results