Posted by: ericgrimsrud | July 17, 2015

Are our plants about to turn on us?

First, consider the following facts.  Over the Industrial Age, mankind caused the emission of about 580 billion tons of carbon into the atmosphere. This has changed the level of atmospheric CO2 from 280 ppm to 400 ppm.  If all of that extra carbon emitted by mankind had stayed in the atmosphere, the level of CO2 today would have been 550 ppm rather than 400 ppm.  Thus, we know that only 40% of the extra carbon emitted stayed in the atmosphere and about 60% went elsewhere – about 30% to the surface layers of the oceans and about 30% to plants.

So yes, what the Deniers like to say “CO2 is plant food” is true at the moment – even though the atmosphere does not like the 40% it gets (because of the global warming it causes) and the oceans do not like the 30% they get (because of the increase in acidity it causes).  And now even that simple statement about “plant food” is being questioned as it pertains to the future – because plant scientists are finding that plants are becoming stressed by changes associated with climate change.

Increased levels of carbon dioxide have caused plants to grow faster, but in the process other nutrients, such as nitrogen and phosphorous, that are required for further growth have become limiting factors.  In addition water levels and climate conditions have worsened in many regions.  All of this appears to be reducing the ability of plants to soak up that 30%  portion of mankind’s extra emissions.  In addition, as the ocean surfaces warm and become more acidic, the oceans are also expected to take up a continuously smaller portion of the excess carbon.

Therefore, an increasing fraction of our total carbon emissions in the future are expected to stay in the atmosphere because plants and the oceans are expected to take up less of it.  In addition, as global warming continues we can expect to see some vegetation that used to be sinks for carbon turn into actual sources of carbon.  One example of this is the organic matter presently stored in the permafrost of the Arctic.  As those regions of the world get warmer, that organic matter will be broken down by microbes and converted to gaseous CO2.  Also an increase in the death of trees in some of our most massive rain forests is being noted and as they decay CO2 is emitted.

Since none of these factors have been included, to date, in the IPCC’s estimates of future CO2 levels, our “allowed” future emissions of carbon – if we are not to exceed a temperature increase of 2.0 C – will have to be significantly lowered  relative to previous estimates.  Thus, when we hear today that we have just 35 years left at current emissions rates before we cross the dangerous climate change threshold, we should reduce that time limit by 5 to 10 years.  All of this is because nature will be quietly boosting her own carbon emissions over the coming decades and an increasingly larger fraction of all emissions, both natural and man-caused, that will be staying in the atmosphere.

Sorry, but that appears to be the way the mop will be flopping. Those hoping for an easy way out of the corner we have painted ourselves into will continue to be disappointed.  Gosh, it would be nice to be able to be a Denier – if only I weren’t cursed with a knowledge of the science involved!

For more details and references to these sobering additional insights, see:

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