There is a growing need for skilful predictions of climate up to a decade ahead. Decadal climate predictions show high skill for surface temperature, but confidence in forecasts of precipitation and atmospheric circulation is much lower. Recent advances in seasonal and annual prediction show that the signal-to-noise ratio can be too small in climate models, requiring a very large ensemble to extract the predictable signal. Here, we reassess decadal prediction skill using a much larger ensemble than previously available, and reveal significant skill for precipitation over land and atmospheric circulation, in addition to surface temperature. We further propose a more powerful approach than used previously to evaluate the benefit of initialisation with observations, improving our understanding of the sources of skill. Our results show that decadal climate is more predictable than previously thought and will aid society to prepare for, and adapt to, ongoing climate variability and change. There is increasing demand for near-time climate predictions to provide guidance for adaptation planning at policy-relevant timescales. Although previous work has shown some skill in forecasting decadal surface temperature, it has proven more difficult to make predictions for precipitation and atmospheric circulation. By using a large, multi-model ensemble of climate models, a multi-institution team lead by Doug Smith of the Met Office Hadley Centre, UK were able to make skillful decadal predictions for near surface temperature, precipitation for the Sahel and broad swathes of Europe and Eurasia, and mean sea level pressure for many regions, with some exceptions being predictions for the South Atlantic and Southern Ocean. Further work is needed to understand whether the instances in which forecasts and observations differ are due to internal variability or external factors such as solar variability, volcanoes and anthropogenic aerosols.

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Robust skill of decadal climate predictions

The predictability of the quasi-biennial oscillation (QBO) is examined in initialized climate forecasts extending out to lead times of years We use initialized retrospective predictions made with coupled ocean-atmosphere climate models that have an internally generated QBO We demonstrate predictability of the QBO extending more than 3 years into the future, well beyond timescales normally associated with internal atmospheric processes Correlation scores with observational analyses exceed 07 at a lead time of 12 months We also examine the variation of predictability with season and QBO phase and find that skill is lowest in winter An assessment of perfect predictability suggests that higher skill may be achievable through improved initialization and climate modeling of the QBO, although this may depend on the realism of gravity wave source parameterizations in the models Finally, we show that skilful prediction of the QBO itself does not guarantee predictability of the extratropical winter teleconnection that is important for surface winter climate prediction

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Predictability of the quasi‐biennial oscillation and its northern winter teleconnection on seasonal to decadal timescales

Predictability on seasonal time scales over the North Atlantic–Europe region is assessed using a seasonal prediction system based on an initialized version of the Max Planck Institute Earth System Model (MPI-ESM). For this region, two of the dominant predictors on seasonal time scales are El Nino–Southern Oscillation (ENSO) and sudden stratospheric warming (SSW) events. Multiple studies have shown a potential for improved North Atlantic predictability for either predictor. Their respective influences are however difficult to disentangle, since the stratosphere is itself impacted by ENSO. Both El Nino and SSW events correspond to a negative signature of the North Atlantic Oscillation (NAO), which has a major influence on European weather.This study explores the impact on Europe by separating the stratospheric pathway of the El Nino teleconnection. In the seasonal prediction system, the evolution of El Nino events is well captured for lead times of up to 6 months, and stratospheric variability is re...

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Seasonal Predictability over Europe Arising from El Niño and Stratospheric Variability in the MPI-ESM Seasonal Prediction System

A new eddy-permitting ocean reanalysis has been recently completed at ECMWF. It is called Ocean ReAnalysis Pilot 5 (ORAP5), and it spans the period 1979–2012. This work describes the new system, evaluates its performance, and investigates how the estimation of climate indices are affected by the assimilation system settings. ORAP5 introduces several upgrades with respect to its predecessor ORAS4, including increased horizontal and vertical resolution, an prognostic sea-ice component, new versions of the ocean and data assimilation system, revised surface fluxes, new version and treatment of satellite sea surface height data, and assimilation of sea-ice concentration, among others. ORAP5 shows similar performance to ORAS4, with improvements in the northern extratropics (especially in salinity), and slight degradation in the Southern Ocean, probably because the observations are insufficient to constrain the increased level of variability in ORAP5. The sensitivity experiments show that superobbing of altimeter data and correlation length-scales of the background errors have a visible impact on the time evolution of global steric height and its partition into thermo/halo-steric contributions. The sensitivities are especially large in the pre-Argo period, when there is the risk of producing unrealistic steric height variations by overfitting the altimeter data. Compared with a control run without data assimilation, all the assimilation experiments also show stronger variability in the halosteric component in the pre-Argo period. The results highlight the importance of sub-surface observations to assist the assimilation of altimeter data, and the need of using a variety of metrics for evaluating ocean reanalysis systems.

The new eddy-permitting ORAP5 ocean reanalysis: description, evaluation and uncertainties in climate signals

Mittelfristige Klimaprognose (MiKlip), an 8-yr German national research project on decadal climate prediction, is organized around a global prediction system comprising the Max Planck Institute Earth System Model (MPI-ESM) together with an initialization procedure and a model evaluation system. This paper summarizes the lessons learned from MiKlip so far; some are purely scientific, others concern strategies and structures of research that target future operational use.Three prediction system generations have been constructed, characterized by alternative initialization strategies; the later generations show a marked improvement in hindcast skill for surface temperature. Hindcast skill is also identified for multiyear-mean European summer surface temperatures, extratropical cyclone tracks, the quasi-biennial oscillation, and ocean carbon uptake, among others. Regionalization maintains or slightly enhances the skill in European surface temperature inherited from the global model and also displays h...

MiKlip - a National Research Project on Decadal Climate Prediction

[1] We introduce an improved initialization to the decadal predictions performed for the Mittelfristige Klimaprognosen (MiKlip) project based on the Max-Planck-Institute Earth System Model and furthermore test the effect of increased ocean and atmosphere model resolutions. The new initialization includes both a more sophisticated oceanic initialization and additionally an atmospheric initialization. We compare the performance of retrospective decadal forecasts over the past 50 years with that of the previous system. The new oceanic initialization considerably improves the performance in terms of surface air temperature over the tropical oceans on the 2–5 years time scale, which also helps to improve the predictive skill of global mean surface air temperature on this time scale. The higher model resolution improves the predictive skill of surface air temperature over the tropical Pacific even further. Through the newly introduced atmospheric initialization, the quasi-biennial oscillation exhibits predictive skill of up to 4 years when a sufficiently high vertical atmospheric resolution is used.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2013GL058051

K. Kulkarni

Papers

Improved forecast skill in the tropics in the new MiKlip decadal climate predictions