Having set up his themes in the previous instalments of the Ring in the Royal Opera’s past two seasons, Barrie Kosky relaxes a little in Siegfried, the cycle’s third part, the ‘scherzo of the symphony’ as it is sometimes regarded. The now familiar leitmotivs of his interpretation as a parable about climate change and the despoliation of the earth are there – the personification of the latter (Erda...