North Atlantic climate far more predictable than models imply

• Published in: Nature
• Main Authors: Smith, DM, Scaife, AA, Eade, R, Athanasiadis, P, Bellucci, A, Bethke, I, Bilbao, R, Borchert, LF, Caron, LP, Counillon, F, Danabasoglu, G, Delworth, T, Doblas-Reyes, FJ, Dunstone, NJ, Estella-Perez, V, Flavoni, S, Hermanson, L, Keenlyside, N, Kharin, V, Kimoto, M, Merryfield, WJ, Mignot, J, Mochizuki, T, Modali, K, Monerie, PA, Müller, WA, Nicolí, D, Ortega, P, Pankatz, K, Pohlmann, H, Robson, J, Ruggieri, P, Sospedra-Alfonso, R, Swingedouw, D, Wang, Y, Wild, S, Yeager, S, Yang, X, Zhang, L
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Research 2020
• Subjects: North Atlantic; North Atlantic oscillation
• Online Access: http://hdl.handle.net/10871/122980; https://doi.org/10.1038/s41586-020-2525-0

This is the author accepted manuscript. The final version is available from Nature Research via the DOI in this record Data availability: The datasets analysed in this study are available from the CMIP data archives: https://esgf-node.llnl.gov/projects/cmip5/ and https://esgf-node.llnl.gov/projects/cmip6/. NCAR data are available from http://www.cesm.ucar.edu/projects/community-projects/DPLE/. Code availability: The code used in this study is available from the corresponding author on reasonable request. Note that the title of the author accepted manuscript is different from the title of the final published version Quantifying signals and uncertainties in climate models is essential for the detection, attribution, prediction and projection of climate change. Although inter-model agreement is high for large-scale temperature signals, dynamical changes in atmospheric circulation are very uncertain. This leads to low confidence in regional projections, especially for precipitation, over the coming decades. The chaotic nature of the climate system may also mean that signal uncertainties are largely irreducible. However, climate projections are difficult to verify until further observations become available. Here we assess retrospective climate model predictions of the past six decades and show that decadal variations in North Atlantic winter climate are highly predictable, despite a lack of agreement between individual model simulations and the poor predictive ability of raw model outputs. Crucially, current models underestimate the predictable signal (the predictable fraction of the total variability) of the North Atlantic Oscillation (the leading mode of variability in North Atlantic atmospheric circulation) by an order of magnitude. Consequently, compared to perfect models, 100 times as many ensemble members are needed in current models to extract this signal, and its effects on the climate are underestimated relative to other factors. To address these limitations, we implement a two-stage post-processing ...