The prospect of a prolonged period of low inflation might have adverse effects, including a possible de-anchoring of inflation expectations. This is why, after setting our policy rates to their effective lower bound, the ECB has decided to engage in a mix of further unconventional monetary policy measures.
In Japan, as well, energy use has declined as a fraction of GDP, but these savings were largely achieved in previous decades, and energy intensity has been flat more recently. We can expect similar increases in oil efficiency in the rapidly growing economies of East Asia as they respond to the same set of market incentives.