INADEC · Impacts of the North Atlantic Decadal variability on European Climate: mechanisms and predictability

Impacts of the North Atlantic Decadal variability on European Climate: mechanisms and predictability

"Will it be raining less in ten years? If so, by how much?” Those are the kind of questions climate scientists attempt to answer more and more accurately. Knowing precisely how the climate of the next decade is going to evolve would provide valuable information for the energy/industry sectors and decision-makers. However, to supply reliable information, several scientific and technical barriers remain to overcome. The project INADEC brings new knowledge that will contribute to open those barriers. At decadal timescales, the climate variability is mostly driven by oceanic fluctuations. In the North Atlantic basin, slow variations in currents and heat transport translate into a general warming or cooling of the whole North Atlantic that typically last for 20-30 years. Those variations are called Atlantic Multidecadal Variability (AMV). These changes in the ocean conditions impact the atmospheric circulation and subsequently the climate conditions of the climate conditions over continents as well as in other oceanic basins. Regionally, those impacts are superimposed to the global warming signal, either minimizing or amplifying it over several decades. Impacts of the AMV include the links between the North Atlantic ocean warming and drier conditions over the Mediterranean region, Mexico, and south-western United States; cooling in the tropical Pacific; and rainier conditions over the Brazilian Nordeste, the Sahel and South-East Asia. Given the worldwide impacts of the AMV variability, predicting its future evolution has the potential for improving our ability to predict the climate conditions over many regions of the world during the next decades, providing valuable information for the energy/industry sectors and decision-makers. Numerical climate predictions show that the North Atlantic region is the most predictable region of the world at decadal timescales. This high predictive skill is encouraging for the prospect of getting skilful decadal predictions all over the globe through the North Atlantic teleconnections. To date, however, decadal climate predictions show only limited skill over continents, with no real contribution coming from the prediction of the AMV. Given the observed teleconnections associated with the AMV, this absence of additional skill over continent raises questions. The INADEC project aimed to evaluate our ability to predict the AMV climate impacts and to identify the current obstacles limiting their predictability. In particular, the project addressed three questions: Q1) Do the observed teleconnections between the AMV and Europe, Sahel, Americas, South-East Asia, and the tropical Pacific ocean have a physical basis? Q2) Can the models simulate those teleconnections accurately? Q3) What are the mechanisms driving the North Atlantic decadal variability and predictability? Results from the INADEC project revealed that the mean model biases are limiting our capability to predict the climate impacts of the AMV. Moreover, the INADEC project shows that large inter-model disagreements exist in the mechanisms that drove the observed AMV since 1950, raising questions about the ability of the current climate model generation in reproducing such mechanisms. Consequently, this suggests that decadal prediction systems can be substantially improved.

Data: CORDIS, © European Union