Climate change, El Niño, cold winters, and California’s drought

Vegetation growth for late January 2014. Brown is below average; green is above average. The green areas in the Sierra Nevada mountains would normally be covered in snow at this time of year.

NASA Earth Observatory/Jesse Allen

It was a winter Charles Dickens would write an opening line about. Parts of the Midwest and Eastern US experienced periods of bitterly cold weather delivered from the Arctic by the jet stream. The West Coast, meanwhile, received very little precipitation—producing a historic drought in California that looms large over the coming summer—as a result of the jet stream zagging in the opposite direction.

The detours of the jet stream were large, and they were persistent. The northward-bending “ridge” shielded the West Coast from moisture-bearing weather that would normally water the Californian landscape and restock the supply of mountain snow that provides meltwater over the dry summer.

Many wondered if climate change could be partly responsible—a question that gets asked about every extreme now. It is, as always, a difficult question to answer, considering the inherent and substantial variability of weather. However, it’s also plainly true that average atmospheric conditions have changed over the past century. The hard part is teasing out the contribution of those changing conditions to specific weather events.