the flows (fluxes). Reducing the energy production from fossil fuels is one possibility, increasing the uptake of the biosphere, soils or marine waters would be another
one. Increasing the uptake of carbon in the biosphere would simply mean to increase
the global photosynthesis rate. However, more photosynthesis normally means more
respiration as well with the effect that this contribution of eliminating carbon from
the atmosphere is limited.
The numbers in Table 2 (cf. Bar-On et al. 2018) indicate that the biomass of
humans and livestock meanwhile is c. 15–20 times larger than the biomass of all
wild mammals and birds together. According to data from the FAO (2018) the global
aquaculture finfish production increased from c. ten million tonnes in 1990 to c. 50
million tonnes in 2015 (c. 56 in 2018; note that published numbers often refer to
fishery products, not only to capture and production of finfish, and include the
production of algae, mussels, and crustaceans, for example). Aquaculture is still
one of the fast growing sectors of the trade of natural products and will continue to
increase. It can be expected that fish produced by farming will equal the capture of
wild fish within the next years or decades as the amount of wild fish harvest has been
stagnant for the last 15–20 years. However, at the moment the capture of wild fish
still exceeds the production of fish from aquaculture. We estimate that the amount of
wild fish currently is at least five times larger than the mass of fish living in
aquaculture (Table 2).
However, the numbers also show that most reservoirs and fluxes are not
influencable by humans (or only little influenced). Exceptions are quantities in
burning fossil fuels, cement production, land use change, agriculture, aquaculture
and forestry. It is a prominent idea to eliminate carbon from the atmosphere via
planting of trees. The numbers related to carbon of reservoirs in plants and fluxes,
however, show that this effect under more or less realistic conditions could only be
rather small (cf. Popkin 2019). This has to do with the fact that almost all of photosynthesis is compensated by respiration. E.g., a further elimination of 200 PgC via
tree plantations would require the range of an additional continent and a time of at
least 100–200 years. And this small effect could only be reached if we start the whole
plantation right now.
The preferential area for more realistic carbon sequestration might be agricultural
land, because of several reasons. First, according to numbers in CIA (2019; own
calculation based on country-related numbers) agricultural fields already cover a
third of the terrestrial ground. Arable land and permanent crops together cover 11%.
Second, in many regions the biodiversity, water quality and productivity would
profit from a higher amount of dead organic matter in the soil (Rice 2002). Third,
storage of carbon in the soil would not require long distances of transportation.
According to calculations in Zomer et al. (2017) the sequestration potential of just
cropland soils amounts to 0.9 (medium sequestration scenario) to 1.85 Pg C/year
(high sequestration scenario). These numbers are related to cropland that already
exists.
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C. Hobohm and S. E. Vanderplank
one. Increasing the uptake of carbon in the biosphere would simply mean to increase
the global photosynthesis rate. However, more photosynthesis normally means more
respiration as well with the effect that this contribution of eliminating carbon from
the atmosphere is limited.
The numbers in Table 2 (cf. Bar-On et al. 2018) indicate that the biomass of
humans and livestock meanwhile is c. 15–20 times larger than the biomass of all
wild mammals and birds together. According to data from the FAO (2018) the global
aquaculture finfish production increased from c. ten million tonnes in 1990 to c. 50
million tonnes in 2015 (c. 56 in 2018; note that published numbers often refer to
fishery products, not only to capture and production of finfish, and include the
production of algae, mussels, and crustaceans, for example). Aquaculture is still
one of the fast growing sectors of the trade of natural products and will continue to
increase. It can be expected that fish produced by farming will equal the capture of
wild fish within the next years or decades as the amount of wild fish harvest has been
stagnant for the last 15–20 years. However, at the moment the capture of wild fish
still exceeds the production of fish from aquaculture. We estimate that the amount of
wild fish currently is at least five times larger than the mass of fish living in
aquaculture (Table 2).
However, the numbers also show that most reservoirs and fluxes are not
influencable by humans (or only little influenced). Exceptions are quantities in
burning fossil fuels, cement production, land use change, agriculture, aquaculture
and forestry. It is a prominent idea to eliminate carbon from the atmosphere via
planting of trees. The numbers related to carbon of reservoirs in plants and fluxes,
however, show that this effect under more or less realistic conditions could only be
rather small (cf. Popkin 2019). This has to do with the fact that almost all of photosynthesis is compensated by respiration. E.g., a further elimination of 200 PgC via
tree plantations would require the range of an additional continent and a time of at
least 100–200 years. And this small effect could only be reached if we start the whole
plantation right now.
The preferential area for more realistic carbon sequestration might be agricultural
land, because of several reasons. First, according to numbers in CIA (2019; own
calculation based on country-related numbers) agricultural fields already cover a
third of the terrestrial ground. Arable land and permanent crops together cover 11%.
Second, in many regions the biodiversity, water quality and productivity would
profit from a higher amount of dead organic matter in the soil (Rice 2002). Third,
storage of carbon in the soil would not require long distances of transportation.
According to calculations in Zomer et al. (2017) the sequestration potential of just
cropland soils amounts to 0.9 (medium sequestration scenario) to 1.85 Pg C/year
(high sequestration scenario). These numbers are related to cropland that already
exists.
92
C. Hobohm and S. E. Vanderplank