Carbon Cycle Basic Questions
Black numbers in the diagram are the estimated natural carbon fluxes (arrows) and reservoirs (boxes).
Red numbers in the diagram are anthropogenic changes since the industrial revolution (1800). Reservoir
units are PetaGrams (Pg) or Giga Tonnes (GT) carbon and for fluxes Pg/yr. This figure was in Chapter 7
of the IPCC 2007 4th assessment report, estimates are for the mid 1990s.
http://www.gfdl.noaa.gov/pix/research/climate_ecosystems/AnthropogenicCarbonCycleBox2.png
1. How much carbon has been extracted from earth’s subsurface by humans between 1800 and
the mid 1990s? ______________________ (Pg)
2. How much carbon has been extracted from earth’s biosphere as a result of land use changes
between 1800 and the mid 1990s? ______________________ (Pg)
3. How much total carbon was extracted from earth’s subsurface and earth’s biosphere since
1800? ___________ What fraction of this total is from fossil fuel extraction? _____________
and what fraction is from land use changes?_______________________
4. How much of this carbon total anthropogenic carbon was still in the atmosphere in the mid
1990s? ________________ (Pg)
5. What percentage of all carbon emitted into the atmosphere by humans was still in the
atmosphere in the mid 1990s? ____________________
6. How much of this anthropogenic carbon was taken up by the oceans? ________________
7. In the mid 1990s how fast was carbon being injected into the atmosphere by fossil fuel
combustion? __________________________ (Pg/yr)
8. In the mid 1990s how fast was carbon being injected into the atmosphere from changes in land
use (deforestation is an example)?_______________________ (Pg/yr)
9. What fraction of the total anthropogenic emissions came from land use changes in the mid
1990s? __________________
10. The figure above suggests that 0.2 PgC/yr are being removed from the climate system by platetectonic subduction. In the natural environment (per-industrial revolution) this removal rate is
in balance with carbon emitted into the atmosphere from volcanic eruptions and other out
gassing mechanisms. So we can infer that the natural carbon fluxes into the atmosphere are
also about 0.2 PgC/yr. How does this compare to the estimates of anthropogenic fluxes of
carbon into the atmosphere? _________________________________________
11. Aside from the atmosphere, where has most of the anthropogenic fossil fuel carbon gone since
it was put into the atmosphere? _________________________________________
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Answers
1. How much carbon has been extracted from earth’s subsurface by humans between 1800 and
the mid 1990s? ______244________________ (Pg) Note: 1 Pg = 1Gtonne
2. How much carbon has been extracted from earth’s biosphere as a result of land use changes
between 1800 and the mid 1990s? _______39_______________ (Pg)
3. How much total carbon was extracted from earth’s subsurface and earth’s biosphere since
1800? ____283_Pg______ What fraction of this total is from fossil fuel extraction?
___86%__________ and what fraction is from land use
changes?___14%____________________
4. How much of this carbon total anthropogenic carbon was still in the atmosphere in the mid
1990s? _____165_____ (Pg)
5. What percentage of all carbon emitted into the atmosphere by humans was still in the
atmosphere in the mid 1990s? _____58%_______________
6. How much of this anthropogenic carbon was taken up by the oceans?____118 Pg____________
7. In the mid 1990s how fast was carbon being injected into the atmosphere by fossil fuel
combustion? _______6.4__________ (Pg/yr)
8. In the mid 1990s how fast was carbon being injected into the atmosphere from changes in land
use (deforestation is an example)?________1.6_________ (Pg/yr)
9. What fraction of the total anthropogenic emissions came from land use changes in the mid
1990s? ___about 20% = 1.6/8.0________
10. The figure above suggests that 0.2 PgC/yr are being removed from the climate system by platetectonic subduction. In the natural environment (per-industrial revolution) this removal rate is
in balance with carbon emitted into the atmosphere from volcanic eruptions and other out
gassing mechanisms. So we can infer that the natural carbon fluxes into the atmosphere are
also about 0.2 PgC/yr. How does this compare to the estimates of anthropogenic fluxes of
carbon into the atmosphere? _____about 2.5 % of the anthrop[ogenic flux___________
11. Aside from the atmosphere, where has most of the anthropogenic fossil fuel carbon gone since
it was put into the atmosphere? _________________________________________