NAO: Driving Climate Across the Atlantic

NAO Who?

Drought in the Middle East. Canadian cod fisheries gone bust. Spine-buckling cold snaps in New England. Brown tides staining Long Island coasts.

Name any debacle of nature, and someone will likely blame it on that bad seed of climatology: El Niño. But there’s another large-scale climate pattern that’s been overlooked. It’s El Niño’s fickle Nordic sister, the North Atlantic Oscillation. First noticed by Norse seafarers many centuries ago, the NAO is the most significant driver of climate variability in the middle and high latitudes of the Northern Hemisphere. It regularly stirs up trouble in Europe, Canada, and the eastern US, and is the leading suspect in the four natural mishaps above. At this point, we ask: Can the NAO get a little respect? And a better stage name?

Historically speaking, as a climate pattern the NAO tends to flip-flop between two phases over the course of years. These phases are dubbed positive and negative, reflecting numerical differences in regional air pressure that drive each phase. Each of the seesawing phases can afflict land, ocean, and air with alternating drama. One winter, for example, the NAO may be cooking French Riviera beaches with a dry heat wave. The next winter, it’s soaking them with storms.

Many mysteries remain about the NAO. But researchers do have a decent grasp on what it can do to everyday Northern Hemisphere folks. Have you, or people you know, had any of the experiences below in the last decade? If so, then you may have been graced by the NAO’s recent inclination towards a positive phase.

Seen fewer snow days?
Mild winters for the US east coast and Northern Europe, with warmer temperatures, less snow, and fewer nor'easters, are a favorite gift of positive NAO phases. They’ve even been linked with warmer winters in cities much farther-flung across the Northern Hemisphere, including Seattle, Dallas, Paris, and Tokyo.

Considered cod a rare delicacy?
Canadian Atlantic cod landings have been slumping for decades, sinking from 2 million tons in the 60s to just 35,718 tons in 2002. Repeated positive NAO phases have been offered as a cause, driving colder waters into the Labrador Sea near Newfoundland. Extra-chilly water slows cod growth and reproduction rates, resulting in runty fish—and the official closure of three essential cod fishing zones in 2003. 

Hosted a visitor from Norway?
If so, maybe it’s because they’ve had more cash for a transatlantic vacation, thanks to lower energy bills during a positive NAO year. Positive-phase winters soak Norway with wetter weather, bringing abundant streamflow for hydropower plants come spring. That’s a surplus of energy—and pocket change.

Eaten very few Long Island bay scallops?
The scallop fisheries on eastern Long Island coasts remain devastated after repeated “brown tides,” or algal blooms, in the 80s and 90s. Brown-tide algae starve bay scallops by paralyzing their feeding mechanisms. Some scientists suggest that yearly variations in the NAO phase trigger surges of nutrients on which brown-tide algae flourish.

Known a soldier working on water access in Iraq?
Positive NAO phases spin fewer storms into Turkey, parching the headwaters of the Tigris-Euphrates River system. Since the runoff supplies fresh water to ⅔ of the Arabic-speaking population of the Middle East, downstream neighbors Syria and Iraq are directly affected by reduced flow.

Filled up your car?
There’s a chance the gas you’ll pump in coming years will originate from an oil rig redesigned to meet the demands of the NAO. Storminess from repeated positive phases has boosted wave heights by more than 10% in the North Atlantic over the last 50 years. That’s bad news for oil-rig operators in the North Sea between Scotland and Norway—a high, unruly wave overtaking a deck can topple a platform. To brace for these more likely events, oil companies are strengthening and raising the decks of new rigs there.

Sipped a mediocre Portuguese wine?
Positive NAOs are stingy on rainfall during crucial spring growing months in Portugal. That makes for a worse grape harvest come August, resulting in unexceptional local wine—and disappointed vintners. 

(And the Weirdest NAO Effect Award goes to…)
Eaten some cheap, delicious British bread?
Positive winter NAO signs cause less rainfall the following summer in England and Wales. The dry weather results in very robust wheat grains, which apparently bake into the best-quality bread.

So what happens in a negative phase of the oscillating NAO? Directly the opposite of the above. You’d expect to get severe winter weather along the US east coast, more cod, a cash-strapped Norwegian, a wetter Middle East, smaller Atlantic waves, a great glass of Portuguese wine—and lest we forget, crumbly, ill-slicing English bread.

If it seems like you haven’t experienced many negative-phase impacts recently, you’re on the money. That’s because during the past 32 years, the NAO’s normally capricious self has favored the positive phase over the negative one, 25 to 7! This has inspired some head-scratching among researchers. Is this stick-to-itiveness natural for the NAO? Or is it unprecedented, and connected somehow to global warming? To this end, scientists in the last decade have initiated an onslaught of NAO investigations to get a better sense of its mechanisms, effects, and natural cycle over many hundreds of years. The ultimate goal? To build an accurate predictive computer model of the seemingly-erratic NAO, which could be used to powerful cultural and economic ends.

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