Q: When is a ship like a tree?

A: When you can't see the forest for it.

You may have followed some press in the last week or so about a Chinese coal ship, Shen Neng 1, that ran aground on the Great Barrier Reef and spilled some of its fuel oil.  This has caused a regular frenzy in the Aussie media and the global conservation and environmental news-o-sphere.  There have been all sorts of calls for prosecution of the shipping company and new stringent regulations for the transport industry and so on, along with dramatic accounts of the damage the ship did and the risky salvage operation that came next.  But you know what?  I am not worried in the slightest about this incident.  Not that its a good thing - far from it - but this accident is nothing more than a tree, obscuring us from seeing one big and scary forest.

The main reasons I am not especially bothered by the Shen Neng accident are that (1) it affected a very limited area - the G.B.R. is really B.I.G. and one ship can only damage so much of it; and (2) it was a single event in time - this was not a process or an ongoing problem, but a singular disturbance.  Science shows us that the GBR, and reefs in general, are amazingly resilient to violent disturbances like this; a decent cyclone can literally turn a reef upside down, and a couple of years later you'd never know the difference.  Indeed, periodic disturbances may  be really important for maintaining a healthy reef ecosystem.

No, the Shen Neng is just a tree, obscuring us from seeing the forest that really threatens the future of the GBR and all reefs.  Its not the 2km gash that the hull cut in the reef, nor is it the tons of fuel oil leaked into the water; it's the very concept of burning that fuel oil, and burning the thousands of tons of coal that the Shen Neng 1 was carrying.  When you consider all the other ships and all the coal and fuel they were carrying that day and every day, and all the cars in the world, the power plants and so on ... ach, you get my point.  THAT'S what we ought to be worried about, because both of the main effects of increased atmospheric CO2 - warming and ocean acidification - will likely result in unrecoverable damage to All reefs. Everywhere. In our lifetime.  Warming is directly linked to lethal bleaching events, while acidification disrupts the ability of reefs to lay down their skeleton and grow.   Oh yeah, and lets not forget the drowning effects of sea level rise, too.  The more I think about it, the more it seems that jumping up and down about the Shen Neng is hypocritical (coal is one of Australia's biggest exports, after all) and akin to complaining about the deck chair arrangements of another, even bigger, ill-fated ship.  (Ironically, if Titanic sailed today, she probably wouldn't have to worry about icebergs...)

Of course, its a false dichotomy, we should be worried about BOTH the Shen Nengs of the world AND the global climate change/ocean acidification.  But I only have so much energy/capacity for worrying about these things, so with a limited anxiety budget, I feel compelled to focus on the bigger issue and what (if anything) we can do about it - to try to reduce consumption and to try to make sensible decisions that are mindful of how much energy is involved and what the broader impacts might be.

In other words, to worry about the forests - and let the trees take care of themselves.

Ocean Conveyor running AMOC

If you’ve ever seen the disaster movie “The Day After Tomorrow”, then you’ve been introduced to the idea that one day the global ocean conveyor might stop.  Its a pity (or perhaps not) that the movie was such a sensational introduction to the concept, because its a pretty serious possibility.  By way of short explanation: one of the things that makes life possible on this rock is that the ocean redistributes heat that arrives on the earth’s surface between the tropics, sending it to the higher latitudes by way of warm surface currents.  There, the waters are cooled and made more dense (both colder and saltier) by the polar ice caps; they then sink and begin a slow meander back to the tropics, eventually returning to the surface to complete the cycle.  Without effective redistribution of this sort, the tropics would bake and the polar zones would sink into a deep hard freeze (in both cases much more so than “normal”).  The climate in the UK, for example, would be much more like Siberia were it not of the tempering effects of the Gulf Stream continually bringing heat from the Caribbean to the North Sea.  An important point about the conveyor is that it is driven from both ends: by the suns heat near the equator and by the cooling effect of all that ice at the poles.

 Why would the conveyor grind to a halt?  The equatorial heat doesn’t show any sign of stopping; if anything its getting hotter.  No, the biggest fear is for the other driver: if the polar ice caps melt too much, there will no longer be a big enough reservoir to chill and brine the surface waters and they will cease to sink.  Some data from recent years suggested that this was happening, and happening fast.  Well, it seems as though Armageddon isn’t here just yet.  A new paper by CalTech/NASA’s Josh Willis in the journal Geophysical Research Letters uses a more complete data set than ever before to conclude that the conveyor, or more specifically a major section of it called the Atlantic Meridional Overturning Circulation (AMOC - hence the corny title of my post) measured at 41°N (near where it says “Atlantic” on the figure above), is not slowing.  In fact, there is some evidence that it may have sped up marginally in recent years, perhaps in response to warming and expansion of Atlantic waters.  The data were consistent across both satellite sources and sensor arrays deployed in the oceans, so it would seem like a pretty robust study (though I am no physical oceanographer).

I am sure I speak for everyone on the bonnie British Isles when I heave a sigh of relief.

But wait?  What light through yonder ice-shelf breaks?  Tis Greenland, and its seeing more of the sun!  In the very same issue of Geophysical Research Letters, a different group of authors report that ice loss is increasing from the Greenland ice sheet.  This is one of the major impacts of recent climate warming and the greatest contributor to increases in sea level globally.  It would also freshen the north polar waters, further reducing the driving force behind the global ocean conveyor.


My response to this news is to marvel at - and grapple with - the complexity and dynamics of the earth and its climate system.  Scientific results with seemingly opposite implications can come out (in this case in the same journal issue), but without threatening the major underlying pattern; I doubt, for example, that Dr. Willis would disagree with the concept of man-made climate change.  Faced with this seeming contradiction, its perhaps no wonder that many folks grapple with the Big Ideas at the heart of global climate change, and even doubt that it exists at all.  I for one have no doubt  that things are changing, and changing fast.  It may just be that some of the really big features of the climate system (including ocean currents) are slower to respond than others.  Its a bit like turning an oil tanker, which may be an unfortunately apt analogy…

Willis, J. (2010). Can in situ floats and satellite altimeters detect long-term changes in Atlantic Ocean overturning? Geophysical Research Letters, 37 (6) DOI: 10.1029/2010GL042372

Khan, S., Wahr, J., Bevis, M., Velicogna, I., & Kendrick, E. (2010). Spread of ice mass loss into northwest Greenland observed by GRACE and GPS Geophysical Research Letters, 37 (6) DOI: 10.1029/2010GL042460