Archive for October, 2011

Shifting Currents

Thursday, October 27th, 2011

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 Pacific Gyre carries warm water south over the Great Barrier Reef along Australia, and then carries cold water back north along the west coast of South America (seos-project.eu)

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).

The EAC flows south along the east coast of Australia, spinning off eddies and gradually weakening.(bom.govau)

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.

Dude, a very relaxed Green Sea Turtle guides Marlin and Dory riding the EAC southward in the movie Finding Nemo (tumblr.com)

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:

Sea surface temperatures of the North Atlantic as the Gulf Stream flows northeast across it (warmer temperatures are the reds, colder are blues, and intermediate are green (nasa.gov)

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.

Season Creep

Tuesday, October 18th, 2011

Season creep – or more formally, shifts in phenology, the timing of seasonal biological events – provides some of the most familiar and convincing evidence of climate change.

In the northern hemisphere, trees and shrubs are leafing out in spring 2-3 earlier days or more each decade, and holding onto their leaves about a day longer in the autumn. The growing season for crops is 10-20 days longer than it was 30 years ago. Snow and ice melt is occurring earlier. Birds and butterflies are migrating earlier. At the same time plants and animals are extending their ranges northward.

Perhaps even the politicians of Washington, D.C. will notice earlier cherry blossoms (japannewbie.com)

The evidence is strong. The timing of cherry blossom festivals in Korea and Japan date back to the 11th Century, while records of grapevine blooms in Europe extend back about 300 years. Meanwhile, the notes taken by enthused bird watchers everywhere over the past decades are finally useful. The last three decades are different from anything on record.

But what about marine plants, animals and ecosystems? They should be experiencing season creep as well. In fact because the marine environment is less fragmented than the terrestrial, the creep should be even more obvious. Because it is the ocean, though, we have much less baseline information, and far fewer long-term data sets. But now, there too the evidence is accumulating.

The journal Global Change Biology has published many articles on season creep, both terrestrial and marine

For instance, intertidal molluscs including blue mussels and some limpet species are extending northward and breeding earlier. Cod are moving northward in the North Atlantic. Pollock, cod, snow crabs and Grey Whales are all shifting north in the Bering Sea. All of this is correlated with warmer sea surface temperatures.

Many species have moved north into the Bering Sea (pmel.noaa.gov)

In the Irish Sea, cod are being replaced by haddock and jellyfish. In the North Sea, small fish species are coming in from the south, and the number of larger more northern species is declining. In the North Atlantic, planktonic copepods are shifting north at about 23 km/yr. On the coast of Florida, Loggerhead turtles are laying eggs 10 days earlier – and the newly hatched juveniles are mostly female. In the subtidal grass beds of the northern Gulf of Mexico, southern fish species are moving in, while more northern species are disappearing. Again, all correlated with warmer sea surface temperatures.

In marine ecosystems, season creep is occurring everywhere one takes the time to look. We can’t ignore it and continue with ‘business-as-usual’.

The problem, though, is that this is creeping change, not pouncing change, and we hardly notice it. What difference does a day or two shift in phenology really make anyway? But as the average temperature of the planet continues to increase, decade after decade, think how much every ecosystem is going to change.

And these are just responses to rising temperatures. Add in the effects of shifts of ocean currents, the impact of stronger hurricanes, the disappearance of coral reefs. These are not idle predictions, they are all occurring now.

Ecosystem upheaval is underway, and we have little idea of how things will settle out. In fact, with ever rising temperatures, they will never settle out but continue to change and shift.

Willing to bet we will take action?
Don’t bet the farm. Maybe move it north though.

Season creep has also hit professional baseball, football and hockey (inventosport.com)