Wednesday, 23 January 2013

A change of air

As far as I know no-one, no matter how fond they are of our present fast-paced and high-powered lifestyle, is arguing with this graph*.

The red line, which spends most of the interval from April to October each year descending, tells us that there are more plants, busily taking Carbon Dioxide out of the air and using it to build things like leaves, in the Northern hemisphere than there are down South.

The black line tells us that the amount of Carbon Dioxide in the atmsphere we know and love will very soon (i.e. by the time the black line reaches the top right-hand corner of the graph) have increased by a quarter when compared to the amount that, say, Elvis was breathing in to sing "Heartbreak Hotel".

The Green line (not visible on the graph) tells us that this matters, that we all have a hand in what is going on, and that there's a good chance it will end badly for us if we don't change our ways. Worse still, the Green line also tells us that once beyond a certain point, the level of Carbon Dioxide is likely to go on increasing, taking the temperature with it, no matter what we try and do to stop it. Like rolling a rock off the top of a ridge, a small change could cause matters to get out-of-hand.

But you knew that already, so let's park Carbon Dioxide for now and turn our attention to a different gas.

The proportion of Oxygen in the atmosphere has been just under 21% for as far back as anyone cares to remember. But it was not ever thus. Some of the earliest life on Earth, about 3 thousand million years ago, lived and worked in anaerobic conditions, the only Oxygen around at the time being a small amount that had outgassed from the oceans. Just as our hard work today produces the "exhaust" gas Carbon Dioxide, theirs produced Oxygen.

It's possible that these Cyanobacteria (also known, confusingly, as "Blue-green Algae") are the greatest success story ever on the planet: they're still here, both "outdoors" in their own right, and "indoors" photosynthesising within the cells of plants, still merrily chucking out Oxygen. There are both Aerobic and Anaerobic versions, and some can even fix Nitrogen.

Why, therefore, isn't the Oxygen level still rising? There are theories. I like this one:

At Oxygen levels under about 20%, it is impossible for anything to burn. It also turns out that, a few percentage points beyond this, it is difficult for anything remotely inflammable, such as a tree, to resist the temptation to spontaneously combust. So, forest fires start themselves if the level is too high: nothing burns at all, and possibly the entire Animal Kingdom works on a go-slow, if the level dips. Like a rock sitting at the bottom of a valley the Oxygen level will, if given a push, come back to the same old place.

So the atmosphere (including the trees, the Cyanobacteria and us) is in an odd state of equilibrium. Push it in the direction "Change Oxygen" and it comes back. Push it, on the other hand, in the "Change Carbon Dioxide" direction and it does something else altogether. Just like a boulder sitting pretty on a mountain pass (thanks Davison Soper, Particle Physics expert, for the picture).

In fact, unless we can adapt to a new atmosphere as thoroughly as the Cyanobacteria did all those aeons ago, and don't mind the inevitable billions of casualties, you could say we have reached a pretty pass.

*(Technical reference Dr. Pieter Tans, NOAA/ESRL ( and Dr. Ralph Keeling, Scripps Institution of Oceanography (

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