This document discusses evidence that human activities like agriculture and deforestation first altered atmospheric concentrations of greenhouse gases like methane and carbon dioxide in pre-industrial centuries. Natural explanations for observed changes in greenhouse gas cycles have been ruled out. Instead, rice irrigation and extensive land clearing in places like Europe, China, and India beginning around 8,000 years ago likely emitted enough carbon to increase atmospheric concentrations. While gradual, this early anthropogenic warming was already large enough to potentially stop a glaciation in northeastern Canada during the last millennium. The document concludes that human emissions significantly impacted greenhouse gas levels and climate long before the Industrial Era.

1. ESS 433 Frances Lin

2. (chiefly of environmental pollution and pollutants)
originating in human activity – Google
anthropogenic (definition)

3. (chiefly of environmental pollution and pollutants)
originating in human activity – Google
anthropogenic (definition)
UGH!
People..

4. GHGs Basic
• absorb and emit
radiation within the
thermal infrared
range
• affect the
temperature within the
Earth, therefore
responsible for
warming
Formula Contribution
H2O 36 – 72 %
CO2 9 – 26 %
CH4 4 – 9 %
O3 3 – 7 %
Kiehl, J.T.; Kevin E. Trenberth (1997)

5. GHGs Basic
• absorb and emit
radiation within the
thermal infrared
range
• affect the
temperature within the
Earth, therefore
responsible for
warming
Formula Contribution
H2O 36 – 72 %
CO2 9 – 26 %
CH4 4 – 9 %
O3 3 – 7 %
Kiehl, J.T.; Kevin E. Trenberth (1997)

6. Industrial
revolution
The anthropogenic era is generally
thought to have begun when the
industrial revolution began producing
CO2 and CH4 at rates sufficient to alter
their compositions in the atmosphere.

7. Industrial
revolution
The anthropogenic era is generally
thought to have begun when the
industrial revolution began producing
CO2 and CH4 at rates sufficient to alter
their compositions in the atmosphere.
?

8. TAKE HOME
Anthropogenic emissions of CH4 and CO2 first altered
atmospheric concentrations in pre-industrial centuries.
Ruddiman’s explanations:
1) un-match pattern of CH4 and CO2 cycles
2) natural forcing is NOT the cause
3) explanation tied to early agriculture in Eurasia

9. CH4 & CO2 Cyclicity

10. Natural (Monsoonal) Source of CH4
The orbital monsoon theory of
Kutzbach (1981) states that
• ↑summer insolation heats
land and causes air to rise
• rising air ↓Psurface and draws
in moist air from the ocean
• the air rises over high
topography and cools, it drops
moisture in heavy rains
• rains flood wetlands, which
release CH4
www.telegraph.co.uk

11. CH4 :Cyclic Variation
Long-term Vostok CH4 record of Petit et al., 1999
three preceding interglaciations

12. CH4 :Cyclic Variation
• expected pattern continued
until 5000 years ago
• increase could have come
from natural or human
sources, or some combination
of the two

13. CH4 :Cyclic Variation
• ongoing drying trend since
9000 yrs BP across tropical
regions (COHMAP, 1988)
• natural (monsoonal) forcing
could NOT be the cause
• wild rice cultivation started
around 7500 yrs BP (Chang,
1976; Glover and Higham,
1996) and
• rice irrigation, extensive
flooding of wetland, began
near 5000 yrs BP (Roberts,
1998)

14. CO2 :Cyclic Variation
• natural orbital-scale CO2 trends are more complicated
• origins of these CO2 cycles are not yet clear
• why δ18O?

15. Why 18O? Just FYI
• δ18O ∝ global mean temperature
• ↑ δ18O means more liquid water; higher T
• ↓ δ18O means less liquid water; lower T
• record(s) of paleoclimate change

16. CO2 :Cyclic Variation
• near 8000 years ago, CO2
trend began an anomalous
increase that has no
counterpart in any of the
three preceding
interglaciations

17. Previous Explanation for CO2
• natural loss of biomass
• changes in ocean CaCO3 chemistry

18. REASON:
• terrestrial carbon has an average
δ13C value near –25 ‰; ocean
carbon reservoirs close to 0 ‰
• an atmospheric trend towards
negative δ13C values indicates a
growing influx of terrestrial carbon
Natural loss of
biomass
Indermuhle et al.
(1999) proposed
that the 20–25
ppm CO2 increase
during the last
8000 years
resulted from a
slow natural loss of
terrestrial biomass.

19. REASON:
• terrestrial carbon has an average
δ13C value near –25 ‰; ocean
carbon reservoirs close to 0 ‰
• an atmospheric trend towards
negative δ13C values indicates a
growing influx of terrestrial carbon
PROBLEM:
• 85% of the loss remained
unexplained
• the net change simulated by
DEMETER, a process-based
ecosystem model, was minimal
Natural loss of
biomass
Indermuhle et al.
(1999) proposed
that the 20–25
ppm CO2 increase
during the last
8000 years
resulted from a
slow natural loss of
terrestrial biomass.

20. REASON:
• growing forests took CO2 from the
ocean-atm system, and caused
deposition of extra CaCO3 in the
deep ocean
• when forest expansion slowed near
8000 yrs BP, the net extraction of
CO2 ended and caused dissolution
of the ‘excess’ sedimentary CaCO3
previously deposited
• atm CO2 values gradually risen
Change in ocean
CaCO3
chemistry
Broecker et al.
(1999) proposed
that the ocean
could have caused
the late-Holocene
CO2 increase.

21. PROBLEM:
• CO2 ‘rebound’ has been ~4 times
the size of the early Holocene
CO2 level
• no ↑CO2 occurred in any of the
last three interglaciations
Change in ocean
CaCO3
chemistry
Broecker et al.
(1999) proposed
that the ocean
could have caused
the late-Holocene
CO2 increase.

22. To conclude..
Natural forcing 1) natural (monsoonal) source of CH4, 2)
natural loss of biomass and 3) ocean chemistry hypothesis
can be rejected.
By process of elimination… ↑CO2 of the last 8000
years points to an anthropogenic origin.

23. Industrial-era vs. Early-anthropogenic
perspective
A. Industrial-era perspective
suggests that most land
clearance occurred in the last
200 years.
B. Early-anthropogenic
perspective suggests that much
slower but longer pre-industrial
land clearance occurred.

24. Industrial-era vs. Early-anthropogenic
perspective
PROBLEM with Industrial-era
views
• neglects the impact of time
• an enormous amount of
evidence of human
influences on the Eurasian
landscape many millennia
before the industrial era

25. Industrial-era vs. Early-anthropogenic
perspective
Pre-industrial emission Industrial emission
Smaller Larger
Start early 200 years
7800 yr x 0.04 GtC/yr
average = 320 GtC cumulative
total
200 yr x 0.08 GtC/yr average
= 160 GtC cumulative total

26. Earlier Agriculture in Eurasia
• land clearance near 8000 years BP
• deforestation

27. Significant Land Clearance near 8000
years BP
• Europe between 8000
and 7000 yrs BP
• China since 9400 yrs BP
• India since 8500 yrs BP
eastern Mediterranean, Zohary and Hopf (1993)

28. Extensive Deforestation between 8000
yrs BP to 2000 yrs BP
• heavy deforestation
(~50-75%) had occurred
in Southeast Asia
• ‘persistent’ deforestation
(~25%) in north-central
Europe
This total is ∼85–95% of the target needed to validate the
hypothesis that humans caused the rise in CO2 after 8000 yrs
BP.
Roberts, 1998; Lewthwaite and Sherratt, 1980

29. Inconsistency?
QUESTION If this estimate is accurate, how could such a
large anthropogenic warming have escaped notice?

30. Inconsistency?
QUESTION If this estimate is accurate, how could such a
large anthropogenic warming have escaped notice?
One reason is that the warming was spread over 8000
years and thus imperceptibly gradual.

31. Inconsistency?
QUESTION If this estimate is accurate, how could such a
large anthropogenic warming have escaped notice?
One reason is that the warming was spread over 8000
years and thus imperceptibly gradual.
The main reason is that the anthropogenic warming has
been masked by a larger cooling trend caused by
decreasing summer insolation.

32. Effects on Climate
Also, early gas emissions reached a global-mean value
of 0.8◦C (2◦C at high altitudes); large enough to have
stopped a glaciation of northeastern Canada…
Andrews et al.,1976; Willams 1978

33. • A significant part of northeast Canada should then have been
glaciated during the last millennium.

34. • A significant part of northeast Canada should then have been
glaciated during the last millennium.
• Based on δ18O (‘ice volume’) cycles, northeast Canada is overdue
for a glaciation; ice sheets should have begun to grow in the last
3000 to 6000 years (Imbrie and Imbrie, 1980).

35. RECAP
anthropogenic GHGs emissions altered the
atmospheric composition during pre-industrial era
• un-match patterns has been observed in CH4
and CO2 cycles
• natural forcing can be rule out
• rice irrigation, land clearance and deforestation
in Eurasia near 8000 yrs ago are responsible
for the un-match patterns
warming is large enough to stop a glaciation in
northeastern Canada

36. References
Broecker, W. S., Clark, E., McCorckle, D. C., Peng, T.-H., Hajdas, I., and Bonani, G.: 1999, ‘Evidence for a
Reduction in the Carbonate Ion Content of the Deep Sea during the Course of the Holocene’,
Paleoceanogr. 3, 317.
Charlson, R. J., Schwarz, S. E., Hales, J. M., Cess, R. D., Coakley, J. A., Hansen, J. E., and Hoffman, D. J.: 1992,
‘Climate Forcing by Anthropogenic Aerosols’, Science 255, 423.
Imbrie, J. and Imbrie, J. Z.: 1980, ‘Modeling the Climatic Response to Orbital Variations’, Science
207, 943.
Indermuhle, A., Stocker, T. F, Joos, F., Fischer, H., Smith, H. J., Wahlen, M., Deck, B., Masttroianni, D., Blunier, T.,
Meyer, R., and Stauffer, B.: 1999, ‘Holocene Carbon-Cycle Dynamics Based on CO2 Trapped in Ice at
Taylor Dome, Antarctica’, Nature 398, 121.
Kutzbach, J. E.: 1981, ‘Monsoon Climate of the Early Holocene: Climate Experiment with Earth’s Orbital
Parameters for 9000 Years Ago’, Science 214, 59.
Ruddiman, W. F.: 2003, ‘Insolation, Ice Sheets and Greenhouse Gases’, Quat. Sci. Rev. 22, 1597.
Ruddiman, W. F. and Raymo, M. E.: 2003, ‘A Methane-Based Time Scale for Vostok Ice: Climatic Implications’,
Quat. Sci. Rev. 22, 141.
Ruddiman, W. F. and Thomson, J. S.: 2001, ‘The Case for Human Causes of Increased Atmospheric
CH4 over the Last 5000 Years’, Quat. Sci. Rev. 20, 1769.

37. QUESTIONS?