— How the fungi (with help from their friends, the trees) created coal and caused climate change…

With thanks to Susan Goldhor of Wonalancet Outdoor Club for this article and associated illustrations.

It seems that some folks have trouble understanding climate change.  Here’s a simple explanation.

Once upon a time, about 360 million years ago, the plant kingdom started producing trees.  Up until then, plants were limited to softer, shorter products, like moss.   The breakthrough that made trees possible was the invention of lignin; a tough, plastic-like material that contributed structural strength to the cellulose that was all plants had had to work with up until then.  The invention of lignin gave rise to wood and especially to bark, and once wood and bark had been developed, plants could stand upright and trees could evolve.

When the plant kingdom invented lignin, it behaved like a kid who discovers candy; it went overboard.  The first trees had bark that was up to 80 times thicker than modern bark, and about half of that was lignin.  The problem arose when those trees reached the end of their lives; fungi are the major rotters of wood but at that time, no organism on earth had the ability to break down lignin, and especially not lignin in such quantities.  So, as more and more trees died, they simply lay where they fell and turned to peat.  This long period — lasting for about 90 million years — was the Carboniferous era.  When the sea rose to cover the swamps, marine sediments covered the peat and, eventually, heat and pressure transformed these organic remains into coal. 

During those 90 million years, plants sucked up enormous amounts of CO2, which was not released since they couldn’t rot.  CO2 levels in the atmosphere fell and O2 levels rose to a point that generated spontaneous fires.*  All that CO2 was sequestered in the dead trees, which then became coal.  A lot of coal; there are carboniferous beds just below ground level that are almost forty feet deep.

Why so much?  Well, carboniferous forests were especially vast because sea level was lower then leaving large tracts of lowland swamp available for plant growth.  And, since much of our nation and Europe were then hanging around the equator, courtesy of continental drift, we’re the ones who ended up with a lot of buried coal.

Why did the Carboniferous era end?  Well, there were two reasons.  First, the trees calmed down in their production of lignin.  They began to resemble modern trees, with thinner bark, more cellulose and less lignin.  Second, fungi figured out how to break down lignin.   Lignin is so tough (think of bakelite, that black plastic in your grandparents’ telephones) that it can’t really be digested.  No one has developed a lignase enzyme.  What the fungi did was to develop enzymes that generate hydrogen peroxide — a really powerful oxidizing agent — and the peroxide literally explodes the lignin apart.  (How fungi are able to do this without blowing themselves apart is one of their many secrets.)  This is still the only way we know of for lignin to rot.

360 million years passed (give or take a bit).  Continents drifted.  Species arose and went extinct either singly by natural selection or massively through great disasters.  Homo sapiens** evolved and, after about 150,000 years, came up with the industrial revolution.  It’s no surprise that it started first in England and then here, just where the two nations had been joined together on the equator so many millions of years ago.  Mills were built; engines invented; ores smelted; all powered by coal.  More and more coal was dug up and burned; more and more was needed.  Fortunes were made by those lucky enough to own land underlain by coal.  And, as the coal burned, all the CO2 that had been sequestered in it was released.  We reversed 90 million years of the Carboniferous in less than two centuries.  CO2 formed an increasing blanket over the earth, preventing heat from dissipating and changing patterns of air flow and precipitation.  CO2 warmed the ocean, changing currents and expanding water volume, which was already expanded by the ice that the blanket of CO2 had melted and continues to melt.  (How much ice?  Well, in the last decade Antarctica has been losing about 250 billion tons of ice per year.  That’s one and a half trillion tons of ice added to the ocean’s water in the last ten years.  Just from Antarctica.)

And that, my friends, is how the fungi caused climate change.  It’s good to have a culprit.


*These high O2 levels are the reason why insects became so large.  (Dragon flies with wingspans of a yard or so seem to be the poster children for this phenomenon.)  Insects don’t have lungs; they take in oxygen through minute holes called spiracles in their cuticles.  The entry of O2 is passive, driven by the partial pressure of O2 in the atmosphere.  The higher levels of O2 in the Carboniferous era meant that it could penetrate further and allow larger bodies.

**Why are we the only species named “sapiens” meaning intelligent?  Because we’re the only species that got to name ourselves.