Much of the weather on the planet is influenced by changes in the intensity of oceanic winds and currents. Weather patterns change as El Ninos and La Ninas last for a couple of years in the Pacific, and while major oscillations in the the North Atlantic and North Pacific cycle over a matter of decades.
Now, increasingly sophisticated models predict further large-scale changes as a of result of global warming but, given these other naturally occurring patterns of change, detecting them can be difficult.
But not impossible. In the South Pacific, climate models predict that the South Pacific Gyre should shift south, poleward.
The South Equatorial Current flows westward across the Pacific, driven by trade winds just south of the Equator. It then flows southward, part of it as the East Australian Current (the EAC).
You recall the EAC. Marlin and Dora ride it most of the way from the Great Barrier Reef to Sidney in their quest to find Nemo. It may not be the swift ride that the movie suggests, but it flows south at around 4 knots or more, fastest in the summer months when the equatorial trade winds are most intense.
The EAC now reaches 350 km further south than it did just 60 years ago, bringing some warm-water reef fish and sea urchin larvae along with it to the east coast of Tasmania for the first time. The sea urchin species is such a voracious algae-eater that it will probably transform the benthic community just as it has in more northern sites.
So the EAC has intensified, has begun to change marine communities, and will have associated effects on the climate of southeastern Australia – an example of what climate models predict will occur in many other places as currents change in response to climate warming.
A much more complex example is the North Atlantic Gulf Stream, and we really don’t know what’s ahead there. But look at the surface currents and eddies in this astounding and beautiful satellite image:
The Gulf Stream is deflected northeastward, partly by the Cape Hatteras landmass, partly by Coriolus forces. The northern Labrador Current flows south to Cape Cod, and then since it is colder and denser, it is gradually pushed below the Gulf Stream, continuing on southward below it.
Try to imagine a three dimensional picture of these two massive, dynamic, constantly changing currents continuing to mess with each other in ever deeper water. Their interactions modify coastal ecosystems and continental weather patterns on both sides of the Atlantic.
Climate warming will change them further, in ways hard to model because our knowledge of their great complexities is still emerging. But change they will, with profound effects.
Of course, they have always changed, ever since continental drift opened the Atlantic Ocean starting around a hundred million years ago. More recently during the ice ages of the past million years, the Gulf Stream would have stopped flowing until warmer interglacial times returned.
The changes in ocean currents in the past have have been immense, but they have been relatively gradual.
So it’s not the change that is new to the planet. It’s the speed of that change. This is new.