Global Warming is a Red Herring

Version 1.3: December 1, 2002

Robert J. Bradbury
© October 2000, All Rights Reserved
 

This is a work in progress.  It has not been peer reviewed at this time.
Cite it only if you convince yourself of its accuracy.

Early in the 21st century, one of the greatest potential problems facing humanity is global warming [IPCC2000, Gle2000, Maz1998].  Though there are opinions to the contrary [Gro2001, Goo2001, Mic2000, Mar1999, Sin1999, Kre1998, Moo1998], we will assume for the purposes for this paper there is sufficient evidence to suspect it will be a problem.  The primary cause of global warming is the greenhouse effect [Hsu99] caused by the greenhouse gases.  These include:

Methane is a stronger greenhouse gas than carbon dioxide, but carbon dioxide is produced in much greater quantities.

Scientists know that bacteria, if sufficiently supplied with nutrients could replicate to the mass of the earth within 2 days.  Since carbon is a primary constituent of bacteria (~23% [Fre1999]FN1), it is clear that CO2 and CH4 are both food sources for these bacteria.  Given the abundance of these gases, one would presume that the bacteria would rapidly remove them completely from the atmosphere.  The problem is that the nanomachinery required to do this (the protein based enzymes) of the cells have requirements for both energy in the form of ATP (adenosine tri-phosphate) and essential metal co-factors, especially iron.  Scientists have shown the growth of microorganisms in the oceans is limited by iron in the Pacific Ocean [Beh1999] and phosphorus in parts of the Atlantic Ocean [Wu2000].  The implication of this is should humanity decide to fertilize the oceans with the required nutrients, the microorganisms in the oceans could remove all of the CO2 and CH4 that humanity has put into the atmosphere since the dawn of civilization.  Since these microorganisms are at the bottom of the food tree in the oceans, this action would increase the overall food productivity of the oceans.  To study this problem in more detail, we must study three questions:

Excess Atmospheric Carbon

How much excess carbon is there in the atmosphere that would need to be removed to return the Earth to its prehistoric state?  The atmosphere has a mass of 5.14×1015 tons or 5.14 Petatons (Pt).  The current CO2 level is 368.4 ppmv.  This is much higher than range from ~200 ppmv level during the glacial eras and the ~275 ppmv reached during interglacial eras, as determined by the Vostok Ice core data [ORNL].  If we wanted Earth to return to its prehistoric CO2 level, we would need to extract ~200 Pg (2×1014 kg) of CO2 from the atmosphere.  Extracting more than this could tip the planet back into an ice age.  Since CO2 is 27% carbon by weight, this corresponds to 54.3 Pg (5.4×1013 kg).

For an idea of how much this is, it is useful to compare it to an estimated 1998 annual world materials production of 1.2×1013 kg [Bra2000].  This includes materials such as stone, sand, gravel, cement, iron ore, clays, phosphates, lime, gypsum, sulfur, soda ash, copper, feldspar and garnet.  So the amount of excess carbon in the atmosphere by mass is equivalent to approximately 50 years of current production of the materials on which our civilization is based.  So it is doubtful that humanity could afford to remove this carbon through industrial means.  What about the biosphere?

The global biomass is ~4.8×1015 kg, containing an estimated 1.1×1015 kg of carbon [Fre2000a].FN2 This is ~3.7 times the amount carbon that humanity has put into the atmosphere.  So if a means can be found to increase global biomass productivity to sequester the carbon, we can stop the accumulation of atmospheric greenhouse gases and begin to reverse it.

If human body composition holds for microorganisms (needs to be checked), this would imply 3.4×1013 kg P and 2.9×1011 kg Fe are in the global biomass.  Annual U.S. production of these materials is 4.4×1010 kg phosphate rock (primarily for fertilizer), 6.3×1010 kg iron ore, used to produce 5.3×1010 kg pig iron, that combined with recycled materials produces 1.1×1011 kg steel.  So, a modest increase in iron production could certainly be used to fertilize the Pacific Ocean to increase biomass production.  Dealing with the lack of phosphorus however appears to be a more difficult problem.

Carbon Consumption

Estimates are that the Net Primary Production (NPP) of photosynthetically fixed carbon is ~48.5 Pg/yr in the oceans and ~56.4 Pg/yr on land [Fie1998].  This is accomplished by a phytoplankton biomass of ~1 Pg C in the oceans that turns over on a weekly basis.  Of interest is that 98.8% of the biomass is on the land, but ~50% of the fixation is occurring in the oceans [Fal1998].

There are at least four possible ways to increase carbon consumption.

  1. Increase the amount of C fixed, by increasing the efficiency of photosynthesis.
  2. Increase the amount of C fixed, by increasing the biomass doing photosynthesis.
  3. Decrease the extent to which fixed C, is recycled through organisms that respire (protozoa, zooplankton, squid, fish) and as a result return the C to the atmosphere.
  4. Increase the rate at which fixed C is stored in ocean sediments.
Increasing the efficiency of photosynthesis seems feasible, since it only appears to operate at an efficiency of ~30%.  This is particularly true since in phytoplankton, photoinhibition due to UV radiation is known to occur at depths down to 25m [Hel92, Kar90, Reg92, Pré1994]. This depresses the amount of C that is fixed.  It is also true that plants waste a great deal of energy because they do not effectively utilize the energy in each photon.  From 400 to 700nm, the photons absorbed each provide the same amount of energy for carbon fixation.  A strategy that would optimize the energy capture would be to have plankton that could control their density so they would typically remain at specific water depths.  The photosynthetic bacteriorhodopsin (in prokaryotes) or light harvesting antenna and chlorophylls (in eukaryotes) of the phytoplankton would be optimized so that the wavelengths absorbed would correspond to the energy of the photons reaching those depths.  Red would be absorbed at the shallowest depths, followed by orange, yellow, green, blue and finally violet at the lowest depths.  On the very surface would float a layer of organisms filled with UV absorbing molecules, such as melanin and mycosporine-like amino acids (MAAs), designed to absorb the UV and reduce the photoinhibition that occurs when normal light harvesting apparatus are exposed to excess UV.

If we were to double the phytoplankton biomass to 2 Pg, that would allow us to fix another 48 Pg/yr of atmospheric carbon, allowing the complete removal of the 200 Pg of carbon humanity has put into the biosphere in less than 5 years.  How much of the essential nutrients of phosphorus and iron would this require?  The element ratio in marine organisms is 106C/16N/1P/0.005Fe [Cop1983, Fre1999], so the P requirement is 20.4 Gkg and the Fe requirement is 0.53 Gkg, representing 55% and 0.8% of the U.S. annual phosphate rock and iron ore production.  The actual requirements would be somewhat higher as the actual P and Fe fraction in the ore sources varies, ranging from ~20-50%.  The world resources for ammonia production are insufficient to fertilize these organisms.  They would have to harvest nitrogen from the atmosphere as Trichodesmium spp., Anabena, and other species normally do.

What happens to the carbon that is fixed by the phytoplankton?  Fish harvest was only 73.5 million metric tonnes in 1996 [UNFAOF?].  This amount (~0.15×1014 Pg) is less than 1/10 of 1% of the available oceanic NPP, so the reality of the current situation is that most of the carbon fixed has to be ending up at the bottom of the ocean or is reoxidized and returned to the atmosphere by organisms consuming the phytoplankton.

Table 1, breaks down where the NPP occurs, how much is consumed, decomposed and stored.  It can be noted that for all practical purposes, the production (NPP) is managed by phytoplankton.  Most of this production however, is consumed.  Some of it falls to the ocean floor where it is decomposed, ending up as methane or methane clathrates.  The small amount stored is eventually recycled through the subduction of ocean floors under the continental plates and volcanic activity releasing CO2 over long geologic time scales.  The storage column is the actual amount that ends up being sequestered from the biosphere.  It seems clear from the table that the intervention point needs to be in (a) getting the phytoplankton to convert carbon into forms that are less easily recycled, such as CaCO3,FN3 or (b) find a more efficient route between the carbon fixing phytoplankton and higher level species that can provide food.FN4
 

Table 1. Estimates of total NPP by the different primary producers and the destinations for the production.
 Composed from sources discussed in [Dua1996].
Primary Producer
Area
covered
Total
NPP
Herbivory
Decomposition
Storage
 
(106 km2)
  
(Pg C / yr)
    
Oceanic phytoplankton
332
43
24.4   (88%)
14.7 (77.5%)
0.17 (26.5%)
Coastal phytoplankton
 27
  4.5
  1.8   (6.5%)
  1.8 (9.8%)
0.18 (27.0%)
Microphytobenthos
   6.8
   0.34
  0.15 (0.5%)
  0.09 (0.4%)
0.02  (3.1%)
Coral reef algae
   0.6
  0.6 
  0.18 (0.6%)
  0.45 (2.0%)
0       (0.7%)
Macroalgae
   6.8
  2.55
  0.86 (3.1%)
  0.95 (4.2%)
0.01  (1.6%)
Seagrasses
   0.6
  0.49
  0.09 (0.3%)
  0.25 (1.1%)
0.08 (12.0%)
Marsh plants
   0.4
  0.44
  0.14 (0.5%)
  0.23 (1.0%)
0.07 (11.3%)
Mangroves
   1.1
   1.1 
  0.10 (0.3%)
  0.44 (1.9%)
0.11 (17.6%)
Total
  -
53.0
27.8 (52%)
19.0 (36%)
0.65 (1.2%)

Energy Use Efficiency

The 1 Pg of oceanic phytoplankton responsible for capturing ~48 Pg/yr of C, utilize only 7% of the available photosynthetically active solar radiation (PAR) from 400 to 700 nm.  The remainder is absorbed by dissolved organic matter or the water itself.  In contrast, terrestrial plants absorb 31% of the PAR received [Mor1991, Fie1998].

The area requirements for C fixation are large.  The world has:

Yet the oceans only fix 140 gC/m2/yr vs. the 426 gC/m2/yr fixed on land.  If we could increase the amount of PAR utilized in the oceans to that utilized by the land, the oceans could fix  616 gC/m2/yr.  So in the oceans we have substantial room for improvement.

Could we move the carbon fixation effort onto the land?  It seems unlikely.  We already intensively farm most of the land available.  The most efficient crops at fixing carbon, such as sugarcane are adapted for the tropics and would need to be reengineered for temperate climates.  It seems likely that only highly efficient solar cells and molecular nanotechnology based CO2 removal systems (based either on molecular sorters or refrigeration separation technologies) would be able to increase land-based atmospheric carbon fixation to levels significantly over those already occuring (without negatively impacting food production).

Conclusions

It seems clear to the author, that if humanity wants really to do something about the potential for global warming that may be associated with the accumulated levels of greenhouse gases in the atmosphere that there is little that can be done on land at this time.  Changing our forestry or farming practices or reducing our production of the greenhouse gases are not going to significantly reduce the problem we have already created.  The path of greatest promise seems to lie first in providing essential nutrients to the carbon fixing phytoplankton in the oceans and then subsequently to engineer one or more species that allow more efficient use of the energy reaching the oceans and in turn make the fixed carbon available as biomass that can be utilized by humans as sources of energy, or more importantly given our growing population, food.

Footnotes


Working Notes:

  • One barrel of oil is equivalent to 42 U.S. gallons (158.987 liters) and can provide about 5.8 million BTU, or about 143,000 BTU per gallon.  In OECD/IEA publications 1 ton of oil eqivalent = 1.00×1010 cal (IT) = 41.868 GJ = 39.68 MBtu (IT).  One barrel of crude oil is ~0.136 tons.
  • The primary photosynthetic phytoplankton in the ocean are Prochlorococcus sp. and Synechococcus sp.  The primary nitrogen fixing organism is Trichodesmium spp.
  • Rock abundance: Put together by Poldervaart in the 1950s.  [ref]
  • Albelson first computed the amount of organic carbon ever created by living organisms, subsequently revised to 1.55×1022 grams (1.55×1019 kg) by Hunt [ref].  See also: Hunt, J. M., Petroleum Geochemistry and Geology, W. H. Freeman (1979, 1996).
  • Re: Plankton NPP -- if global biomass is 4.8×1015 kg, that is 4800 Pg.  1/4800 = 0.0002 = 0.02%, not 0.2% as Falkowski & Field suggest!  See [Beh1997] to unravel this problem.
  • Useful Links:
  • Global Warming Links
  • GlobalWarming.org

    • References

    UV Radiation

    Nutrient Limitations and Iron Experiments

    Possible Refs
    Created: October 1999
    Last Modified: April 16, 2004