A young forest in a temperate climate, shown in the previous blog, grows fast in a clear-cut area and transfers nutrients from soil to the young trees. The young trees grow very fast (there is a positive net primary productivity or NPP), but the amount of mass accumulated in the forest is small. When a tree burns or dies some or most of its nutrients go back to the soil. When this tree is logged and hauled away, almost no nutrients are returned. After logging young trees a couple of times the forest soil becomes depleted, while the populations of insects and pathogens are well-established, and the forest productivity rapidly declines. When the forest is allowed to grow long enough, its net ecosystem productivity becomes zero on the average.
|Paraphrasing Henry Paulson's famously surprised comments about the 2008 financial meltdown, who would think that there wasn't an infinite supply of these 2000-year old redwoods? Yes, who would ever anticipate that?|
Phosphates are just another form of fossil resource. Over millions of years, the annual cycles of life and death in ocean upwelling zones have propelled sedimentation of organic matter. Critters expire or are eaten, and their shredded carcasses accumulate in sediments as fecal pellets and as gelatinous flocculation termed marine snow. Decay of some of this deposited organic matter consumes virtually all of the dissolved oxygen near the seafloor, a natural process that permits formation of finely-layered, organic-rich muds. These muds are a biogeochemical "strange brew," where calcium -- derived directly from seawater or from the shells of calcareous plankton - and phosphorus - generally derived from bacterial decay of organic matter and dissolution of fish bones and scales - combine over geological time to form pencil-thin laminae and discrete sand to pebble-sized grains of phosphate minerals. Without phosphates there are no living plants or animals. For more information, see Grimm, 1998.
Therefore, to the extent that humans are no longer integrated with the ecosystems in which they live, they are doomed to extinction by exhausting all accessible planetary stocks of minerals, soil and clean water. The question is not if, but how fast? For ancient agriculture the answer seems to be a few thousands of years, with a possible exception of China. For modern agriculture, I would be surprised if it lasts for another century without a major systemic crash.
In the last two blogs, I gave you an abstract proof of no trash production in Earth's Kingdom, except for its dirty human slums. Are there any other, more direct proofs, perhaps based on measurements? It turns out that there are two approaches that complement each other and lead to the same conclusions. The first approach is based on a top-down view of the Earth from a satellite and a mapping of the reflected infrared spectra into biomass growth. I will summarize this proof here. The second approach, also described in my OECD paper, involves a direct counting of all crops, grass, and trees, and translating the weighed or otherwise measured biomass into net primary productivity of ecosystems. Both approaches yield very similar results.
MOD17A2/A3 User's Guide (2003) provides a description of the Gross and Net Primary Productivity estimation algorithms designed for the MODIS instrument aboard of the Aqua and Terra satellites.
MODIS, or the Moderate Resolution Imaging Spectroradiometer, is a key instrument that provides high radiometric sensitivity (12-bit) in 36 spectral bands ranging in wavelength from 0.4 to 14.4 microns, which is the range of infrared radiation emitted by tree canopies, grasses, and the Earth surface. Most of this radiation leaves the Earth and warms up the cold universe. This is the main reason why life can persist on the Earth.
MODIS provides global maps of several land surface characteristics, including surface reflectance, albedo (the percent of total solar energy that is reflected back from the surface), land surface temperature, and vegetation indices. Vegetation indices tell scientists how densely or sparsely vegetated a region is and help them to determine how much of the sunlight that could be used for photosynthesis is being absorbed by the vegetation. MODIS is also very good at detecting deforestation and degeneration of ecosystems.
The bottom line is this:
Over the last 13 years, the measured Gross Primary Productivity of terrestrial plants on the planet Earth has been about 100 gigatons of carbon per year. It changed by plus or minus a few gigatons of carbon from one year to another, because of the changing weather patterns each year. (Remember, the Earth is cyclic.) This is all the carbon sequestered by all of the photosynthesizing terrestrial plants on the Earth. About 1/2 of this mass, 50 gigatons/year, has been maintenance food for these plants. The remaining 50 gigatons of carbon per year have been used up by the same plants to grow and be eaten by all of the Earth's living creatures, some of which then ate other creatures. Almost nothing is left after each orbit. The Net Ecosystem Productivity (NEP, defined in the previous blog) has been about zero for the Earth.So, when someone says that 50 gigatons/year (1800 EJ/year) of biomass carbon are potentially available for our cars, tanks, and jets to burn as fuel, that person should be declared insane, and become a top adviser to the green nonprofits, think tanks, and world governments. This person should also be a media star, simply because we live in an insane world in which money and mass are reported to be created from nothing.
In the next installment, I'll explain to you why modern industrial agriculture must be a long-term failure, and some of its global impacts.