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The Global
Carbon Cycle
“It’s not just for
scientists anymore…”
What we wish to learn:
1. How does the carbon cycle help to explain increasing
temperatures on Earth?
2. What are the major controls on the C cycle, and what
methods of study can we use to determine these
controls?
3. Can we use natural ecosystem processes related to the
carbon cycle in order to slow the rate of greenhouse gas
accumulation in our atmosphere?
Surface
Temperature
Variation
(top) Past 140
years, global
The “Hockey Stick” of change
(bottom) Past
1000 years, N.
Hemisphere only
Greenhouse gas increases are driving temperature rise
400
Atm CO2 conc (ppmv)
390
Atmospheric Carbon Dioxide Curve
Mauna Loa 1958 - 2012
380
370
360
350
340
330
320
ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_mm_mlo.txt
310
Year
The rate of CO2 increase is accelerating
ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_mm_mlo.txt
Indicators of the Human
Influence on the
Atmosphere during the
Industrial Era
CO2 , CH4 , N2O
It’s a “hockey team”
Now commonly referred to as
the next geological epoch, the
“Anthropocene”
Source: IPCC TAR 2001
Global and Continental Climate Change – observations and models
Humancaused
greenhouse
gas increases
have warmed
the world
Models using only natural forcing
Models using both natural and human forcing
Observations
IPCC 2007: WG1-AR4
Intergovernmental Panel on Climate Change, IPCC
Summary statements from the 4th Assessment Report, 2007
“Warming of the climate system is unequivocal, as is now evident from
observations of increases in global average air and ocean temperatures,
widespread melting of snow and ice, and rising global average sea level.”
“The global increases in carbon dioxide concentration are due primarily to
fossil fuel use and land use change, while those of methane and nitrous
oxide are primarily due to agriculture.”
“The understanding of anthropogenic warming and cooling influences on
climate has improved…, leading to very high confidence that the global
average net effect of human activities since 1750 has been one of warming.”
Beware the Arguments and Ploys of Skeptics and Politicians
1. Personal or professional gain
2. Selective use of data (cherry-picking)
1. Scientists must support themselves financially, and the hyping of global warming
leads to more research grants.
"Research is basically a question of revealing truths about ourselves and our
surroundings, be these manmade or natural. But research does not simply come about
of its own accord, it has to be financed. This means that the problems to be investigated
are influenced, to some degree, by the interests of those who finance the research."
pp. 36 in Lomborg, B. 2001. The Skeptical Environmentalist: Measuring the Real State of the World. Cambridge Press, 540 pp.
2. Open Letter on the President’s Position on Climate Change, 7 February 2007:
“Our emissions performance since 2000 is among the best in the world. According to the
International Energy Agency, from 2000-2004, as our population increased and our
economy grew by nearly 10%, U.S. carbon dioxide emissions increased by only 1.7%.
During the same period, European Union carbon dioxide emissions grew by 5%, with
lower economic growth.”
http://www.whitehouse.gov/news/releases/2007/02/20070207-1.html
http://www.whitehouse.gov/news/releases/2007/02/20070207-5.html
The ploy of “cherry-picking data”
+15%
-1%
1992
“Rio”
1997
“Kyoto”
2001
“9/11 recession”
Index of Greenhouse Gas Emissions for the U.S. and European Union
from 1990 to 2004 (Index=100 for 1990, U.N. baseline agreement)
The CO2 concentration in the atmosphere is strongly
correlated with the Earth’s surface temperature
but, there are aspects of the carbon cycle that we don’t understand…
Understanding Global Element Cycles
A Method of analysis:
1. Accounting
2. Cycling and Pathways
3. Controls
(This method applies to all element cycles)
The Global Carbon Cycle
1. Accounting
Rocks
Oceans
Soils
Atmosphere
Land Plants
(x 1015 g C)
65,000,000
39,000
1,580
860
610
Carbon Forms include: Inorganic C (e.g., HCO3-)
Organic C (e.g., CHO compounds)
Gases (CO2, CH4, CO)
The carbon in the atmosphere is 99.6% CO2
+7.9 per year
Atmospheric CO2
860 ( @ 385 ppmv)
+ 3.2 per year
50
60
Global
Carbon
Cycle
~1.4 Net flux
River
Transport
Vegetation 610
Soils 1580
Stock = Billion metric tons
Flow = Billion metric tons per year
~1.7 Net flux
Ocean 39000
90
2. Cycling
(a) Pathways (previous slide)
(b) Fluxes (in “Peta grams”, Pg = 1015 g
= “gigaton” = billion metric tons)
(i)
(ii)
(iii)
(iv)
(v)
Photosynthesis
Respiration
Net Ocean Uptake
Fossil Fuels
Biomass Burning
1015 g/year
= - 111
= + 110
=
- 1.7
=
+6.3
=
+1.6
(c) Mass Balance (of the atmosphere)
Net change = Input + Output + Internal Change
3.2 = (110 + 6.3 + 1.6) + (-111 + -1.7) + 0
3.2 = (117.9) - (112.7)
3.2 = 5.2
* Need a “sink” of (5.2 – 3.2) = 2.0 Pg C / year
to balance the global C budget.
Where is the sink?
Probably in the soils and plants of the Northern Hemisphere
3. Controls
(a) Volcanic Activity
Strong controls over long periods of time, Weak controls over
short periods of time.
(b) Weathering
Strong controls over long periods of time, Weak controls over
short periods of time.
(c) Biological controls
Strong controls over the patterns of carbon flux over short
periods of time (e.g., seasonal)
(d) Human influence
Weak controls over long periods of time, Strong controls over
short periods of time.
(a) Volcanic Activity has a Strong Influence on
Atmospheric CO2 over Long Periods of Time
Over Short Periods of Time, Volcanic
Activity has a Weak Influence on
Atmospheric CO2
• Volcanic Emissions = 0.05 Pg C /yr
• Anthropogenic emissions = 8 Pg C /yr
Therefore, human influences are ~160 times
more important than volcanoes today.
(b) Weathering Reactions Control CO2 in
the Atmosphere over long Geologic Time
(c) Biological controls – affect seasonal patterns
Respiration
N. Hemisphere
S. Hemisphere
Global distribution of CO2
1992-2001
Photosynthetic uptake
(d) Human Influence – CO2 emissions from fossil fuels
and land-use change
Projected CO2
Emissions will be
tied to
Population
Growth
Dec, Jan, Feb
Projected
Changes in Annual
Temperatures for
2100
-- from different
GCM models (A2
emission scenario).
Note that the
temperature
increases are all
greater than the
uncertainty.
Model
predictions
95% confidence
intervals
(uncertainty)
Deg C
From IPCC 2007
How do we solve problems associated with our
altered C cycle and increasing CO2 in the
atmosphere?
1. The “Geritol Fix” – adding Fe to the Southern
Oceans to stimulate algae to take up more CO2
C:Fe = 106:0.01
C:N:P:Fe (!)
Element cycles interact!
2. Carbon Sequestration – can something as
simple as planting trees be the solution?
Can’t we just plant
a bunch of trees?
CO2 uptake = 50 CO2 (with 1 N)
Net atm change
= (25 – 50) = -25
+25 CO2
Plant C:N = 50
25 CO2
OM decomposition
Soil C:N = 25
1 N
Take-home message:
“There are no magic fixes
for the CO2 problem”
Summary:
1. The global carbon cycle is closely tied to Earth’s temperature
through carbon-based greenhouse gases (CO2 and CH4).
2. The recent modification of the carbon cycle by humans has
warmed our globe considerably more than accounted for by
background climate variation.
3. Understanding the carbon cycle requires an accounting of
where the C is stored, the pathways that it travels through
the geosphere and biosphere, and the controls on the rates of
C cycling.
4. Volcanoes and weathering exert control over the global C cycle
only on very long time scales, whereas humans exert control
over very short time scales.
5. There are no simple fixes for the CO2 increases, in part
because element cycles (C, N, P, Fe) are linked and interact.