A Global Warming Curveball: More Upwelling

Amid all the gloomy projections about the effects of climate change, a study in today’s Science reports a new effect that might inject some hope into the sorry state of ocean fisheries: increased upwelling.

What’s upwelling? Funny you should ask. I was surfing in dreadfully cold Monterey Bay water last week when I turned and looked straight in the eye of a surfacing gray whale about 40 meters away. Both my ice-cream headache and the whale’s presence were products of upwelling, a fact of life along the western coast of North America and other continents.

During upwelling, vagaries of wind patterns and fluid dynamics draw very cold, nutrient-laden water up from the depths, freezing surfers’ skulls and kick-starting a food-chain party for krill, squid, fish, seals and whales. (For more specifics, see Bay Nature.) Upwelling zones around the world occupy less than 1 percent of the ocean, but account for 20 percent of the world’s fish catch.

In the new study, Helen McGregor from Germany’s University of Bremen and colleagues used sediment records to reconstruct the sea surface temperature at Cape Ghir, Morocco, over the last 2,500 years (around 2,490 years longer than previous studies of upwelling and climate change). The record showed colder waters – indicative of upwelling – during warm times like the Medieval Warm Period. But the strongest signal by far came during the twentieth century, when water temps dropped by 1.2 degrees C. If the standard air-temperature records look like a hockey stick, the water temperatures look like a mirror image.

But how could global warming do anything to change ocean currents? The authors suggest that more atmospheric CO2 could change the air-temperature balance between coastal land and waters. That would change the prevailing air pressure (i.e., weather systems), and the pressure difference would fuel stronger winds along the coast, stirring more upwelling. (See the Science article for a suitably technical description of this.)

With ocean fisheries in dire trouble (thanks to population growth and the fact that seafood is so yummy), increased upwelling could nourish more fish and slowly help us out of trouble in that respect. Upwelling also brings up centuries-old water that has never seen our CO2-rich atmosphere. That deep water would draw more CO2 out of the atmosphere than a similar amount of surface water. (Although this sounds good from a global-warming standpoint, it would speed the acidification of the oceans, a slowly building nightmare that Elizabeth Kolbert recently discussed for the New Yorker.)

One of the major problems with getting people to take notice of climate change is its complexity: we can’t predict exactly what’s going to happen, and we can’t even assemble a complete list of the kinds of things that will happen. Often, this uncertainty winds up skewed into either a simplistic doomsday scenario or a “jury is still out” assessment – both rather easily dismissable, I’m afraid. Fortunately, the scientists are still out there, assiduously working out the specifics.