Norway’s central bank stunned investors last week by cutting its main interest rate to head off a “severe downturn” due to plunging oil prices. Ninety minutes later, Russia’s central bank raised its benchmark to bolster a currency weakened by crude’s decline.

The split among two of the largest oil exporters shows how the slump in the price of crude to its lowest in five years will make 2015 a year of divergence for global central banks and increased volatility in financial markets.