How Atlantic Warming Brings Pacific Devastation

Some very large part of Western civilization's development comes courtesy of the trade winds. It's these winds that form very large-scale patterns of surface air movement spanning entire hemispheres; a 15th century ship setting sail from Portugal toward the New World just had to latch on and cruise. Eventually, said vessel can be assured of delivery by these winds to the general vicinity of the Bahamas or further into the Caribbean Sea. The trade winds soon enough became the backbone of proto-globalization, and so here we are.

But, just as the trade winds giveth, they may taketh as well. After several decades of global warming, it's now clear that rapidly increasing temperatures in the Atlantic Ocean are having very mobile effects elsewhere on the planet. According to a study out today in Nature Climate Change, this oceanic warming is boosting the Pacific trade winds—those ripping out of the northeast toward the tropical southwest and west—which in turn are having profound climate impacts ranging from an amplified Californian drought to accelerating Pacific sea level rises to, possibly, the long-term suppression of El Nino events.

The Pacific trade winds are currently blowing harder than at any point in their recorded history, which extends back to the 1860s. In fact, this is the opposite of most outcomes predicted by climate models, a mystery explained by still another unexpected climate outcome: rapid warming of Atlantic waters. The heat sponges of the planet's oceans may have helped slow the surface progression of climate change, but that absorption hardly comes free. In this case, Atlantic warming has led to intense pressure differences between the Atlantic and Pacific basins, creating a new gradient between the two zones that helps push/pull air masses from east to west, at least within the lower, tropical latitudes.

"The rapid warming of the Atlantic Ocean created high pressure zones in the upper atmosphere over that basin and low pressure zones close to the surface of the ocean," said Axel Timmermann, the study's co-lead author, . "The rising air parcels, over the Atlantic eventually sink over the eastern tropical Pacific, thus creating higher surface pressure there. The enormous pressure see-saw with high pressure in the Pacific and low pressure in the Atlantic gave the Pacific trade winds an extra kick, amplifying their strength. It's like giving a playground roundabout an extra push as it spins past."

A key effect of the boosted air flow is a rapid "overturning" of Pacific surface waters. As the wind-whipped water churns, it sucks up more atmospheric heat, a process that could help explain the aforementioned recent slowdown in the overall warming of surface temperatures. Even as the Pacific sucks up more heat, the winds keep it cooling overall, at least on the surface, which is something that might explain the recent lack of major El Nino events (which are characterized by abnormal spikes in water temperatures).

In the absence of El Nino conditions, we're faced with climate effects more like those of La Nino— its cooler than average inverse—in which the Atlantic hurricane system often becomes supercharged and the southwestern United States is more likely to experience abnormal dryness, as it is now to disastrous effect.

More properly, the current paper describes increases in what's known as the Walker circulation, or how surface air movements push away from the southwestern US (in this instance), stealing the region's moisture and delivering it to the other end of the Pacific loop, e.g. southeastern Asia. Meanwhile, increases/decreases in this pattern modulate the appearance of El Nino and La Nina events. It was only in 2006 that researchers described quite the opposite phenomenon—a critical slowdown in the Walker winds—to what's being observed currently.

The oceanic temperature uptake overall appears to be a relatively recent feature of climate change, but it's one that can't continue indefinitely or, perhaps, even for very long. "It will be difficult to predict when the Pacific cooling trend and its contribution to the global hiatus in surface temperatures will come to an end," said the current study's co-author Matthew England. Eventually, the situations between the Atlantic and Pacific will equalize, and that hardly means some chilling out in Pacific weather trends. The effect will be a rapid, unprecedented rise in surface air temperatures, as oceans not only stop acting as heat sinks, but stop acting as buffers at all.

Imagine the warming acceleration seen before the current lull (above), but without the benefit of a planet covered in the temperature cushion of cool oceans. Hello, Venus?