The retrospective prediction of El Niño-southern oscillation from 1881 to 2000 by a hybrid coupled model: (I) Sea surface temperature assimilation with ensemble Kalman filter

In this study, we assimilated sea surface temperature (SST) data of the past 120 years into an oceanic general circulation model (OGCM) for El Niño-southern oscillation (ENSO) retrospective predictions using ensemble Kalman filter (EnKF). It was found that the ensemble covariance matrix in EnKF can act as a time-variant transfer operator to project the SST corrections onto the subsurface temperatures effectively when initial perturbations of ensemble were constructed using vertically coherent random fields. As such the increments of subsurface temperatures can be obtained via the transfer operator during assimilation cycles. The results show that the SST assimilation improves the model simulation skills significantly, not only for the SST anomalies over the whole assimilated domain, but also for the subsurface temperature anomalies of the upper 100 m over the tropical Pacific off the equator. Along the equator, the improvement of the assimilation is confined within the mixing layer because strong upwelling motions there prevent the downward transfer of SST information. The retrospective prediction skills of ENSO over the past 120 years from 1881 to 2000 were significantly improved by the SST assimilation at all leads of 1–12 months, especially for the 3–6 months leads, compared with those initialized by the control run without assimilation. The skilful predictions by the assimilation allow us to further study ENSO predictability using this coupled model.     

Lost in the mix: will the technologies of carbon dioxide capture and storage provide us with a breathing space as we strive to make the transition from fossil fuels to renewables?

This paper explores concepts of carbon lock-in arising from the technologies of CO₂ capture and storage (CCS). We examine the argument that CCS reduces carbon lock-in and the calls for a CCS ‘mandate’ and emission performance standards. We analyse the pros- and cons- of a low-carbon fossil fuel lock-in, arguing that lock-in per se is not the problem; it is rather the depth of lock-in which creates problems because deeper lock-in reduces flexibility and increases the ‘error cost’ (i.e. the cost of a decision which turns out to be based on incorrect understanding) and should be avoided. A set of technical and institutional indicators for measuring the flexibility of different technologies is then presented and applied to three technologies: a landfill gas power generator, a conventional nuclear power plant and a CCS plant under development in California. We conclude that these indicators are a useful way forward in assessing individual projects and that public authorities and other stakeholders might wish to employ some version of these indicators in their deliberations on the role of CCS.