The Carbon Cycle

Understanding the carbon cycle is vital to understanding climate change.  Indeed it is vital to understanding life itself.

We all know about the hydraulic cycle.  Evaporation from the oceans rises into the atmosphere, forms clouds, and falls as rain and snow, and the water flows back to the ocean from lakes and rivers.  Of course, some of the water evaporates from land, plants, rivers and lakes, contributing to the cycle.  Some of the water is stored for thousands of years in underground aquifers.

The carbon cycle operates in a similar fashion.  Plants use the energy from the sun to take carbon dioxide (CO2) out of the air, and convert it from a gas to a solid, often sugars, cellulose etc.  When the plant dies, or its leaves or needles fall, that actions of bacteria rot the material, releasing the fixed carbon back into the atmosphere as carbon dioxide.  If the rotting occurs without oxygen, then the bacteria release the carbon as methane (CH4).  This occurs naturally in bogs, animal farts, and unnaturally in landfills.

Carbon is the stuff of life.  All living things are made of carbon.  When we breathe, we take in oxygen, and release carbon dioxide.  Plants do the reverse.  They take in carbon dioxide, and use the carbon to make leaves, roots and stems, and release the oxygen.  The release of carbon dioxide by animals is very small compared to the amount released by bacteria in the rotting process.

So the carbon cycle is continuous.  Plants take in carbon, and animals and bacteria, and sometimes forest fires, release it back to the atmosphere.  We know that the amount of carbon dioxide in the atmosphere has been stable for at least 420,000 years.  We know this from core samples taken in Greenland and Antarctic glaciers.  Every year, snow falls, trapping a bit of the atmosphere of the time, and we can measure the carbon dioxide concentrations.  For 420,000 years, the level varied between about 260 parts per million, and 280 ppm.

There is an extinct volcano in Hawaii where we have been measuring carbon dioxide levels since the 50’s.  The measurements are taken there because it will have minimal influence from surrounding plants, that may vary the local ground levels of CO2.  Every spring, the level of carbon dioxide falls a bit.  And every fall it rises.  The northern hemisphere has the most land, and the decline in CO2 levels is because the plants on the land take carbon dioxide out of the atmosphere in the spring.  Then, when the autumn leaves fall, the bacteria goes to work very quickly, and the carbon dioxide level rises.

But since 1900, the level of CO2 in the atmosphere has risen from 280 ppm to 380 ppm, with only a small seasonal variation.  At the current rate of increase, we will be over 500 ppm by mid century – the rate of increase has been accelerating.

There is a vast store of carbon in the earth, as oil, natural gas, peat, and coal.  There is a considerable store of carbin in the earth’s life as well – the trees, grass, soil, bacteria, coral, sea shells, and animals.  These stores of carbon can be compared to the underground aquifers in the hydraulic cycle.  As we dig up, pump and burn this carbon, we release the CO2 that has been stored on the land for millions of years.

Some climate skeptics have pointed out that there have been times in the distant past where the amount of carbon dioxide in the atmosphere was much higher than today, and life still existed.  And they are right.  Life did exist.  And it will continue to exist, even if we double or triple the carbon dioxide levels in the atmosphere.  Evolution, in time, will ensure that new species will emerge that will thive in the new climate.  But today’s life evolved in the comfortable zone of 260-280 ppm.  Changing the level of CO2 will change the climate, and that will mean many extinctions.  Humans evolved in the 260-280 ppm level.  It was only 30,000 years ago that we shared the earth with neanderthals, a different human type species.  They didn’t make it.  We depend on the species that co-evolved with us for food.  The bacteria in our stomachs, the plants and animals we eat, the species they depend on, all evolved in our current atmosphere.  And many of them will not survive the change.  The fact that there was life of different types of life that could survive in higher CO2 atmosphere doesn’t mean that we will.  Life will evolve, but we may not.

That is why the carbon cycle is important.  And we mess with it at our peril.

Wind energy can play an important role in providing us with carbon free energy.

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