1. The Global Carbon Cycle
“It’s not just for scientists anymore…”
Rainforest Homework Problem

2. Surface Temperature Variation
(top) Past 140 years, global
(bottom) Past 1000 years, N. Hemisphere only

3. Surface temperature monitoring network
1870
1900
1930
1960

4. Variations of the Earth’s Surface Temperature - 1000 to 2100
Combined data & model results:
1000 to 1861, N. Hemisphere — proxy data
1861 to 2000, Global — instrumental
2000 to 2100 Global — model projections
Variations of the Earth’s Surface Temperature: 1000 to 2100
The projected temperature changes from 2000 to 2100 for the 6 illustrative SRES scenarios are shown in comparison to temperatures observed over the last millennium.
The “several models all SRES envelope” shows the temperature rise for the simple model when tuned to a number of complex models with a range of climate sensitivities. All SRES envelopes refer to the full range of 35 SRES scenarios.
Source: IPCC TAR 2001

5. Greenhouse gas increases are driving temperature rise

6. Indicators of the Human Influence on the Atmosphere during the Industrial Era
Concentrations of atmospheric greenhouse gases and their radiative forcing have continued to increase as a result of human activities.
Since 1750, carbon dioxide has increased by 31%, methane by 151% and nitrous oxide by 17%. Present concentrations of CO2 and methane are higher now than at any time during the last 420,000 years, the period for which there are reliable ice core data, and probably significantly longer. The current rate of CO2 increase is unprecedented during at least the past 20,000 years.
About 75% of the anthropogenic emissions of CO2 to the atmosphere during the past 20 years is from fossil fuel burning, the remainder from deforestation and other land-use changes.
The greatest warming effect currently stems from CO2, followed by methane, halocarbons and nitrous oxide.
Cooling effects stem from the depletion of stratospheric ozone and generally from relatively short-lived aerosols. Ice cores in Greenland show the large increase in anthropogenic SO2 emissions during the Industrial Era (graph b).
Source: IPCC TAR 2001

8. The CO2 concentration in the atmosphere is strongly correlated with the Earth’s surface temperature

9. “There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities”
“…most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations”.
IPCC 2001
Global Cycles, Method of analysis:
Accounting
Cycling and Pathways
Controls

10. The Global Carbon Cycle
1. Accounting
(x 1015 g C)
Rocks 65,000,000
Oceans ,000
Soils ,580
Atmosphere
Land Plants
Carbon Forms include: Inorganic C (e.g., HCO3-)
Organic C
Gases (CO2, CH4, CO)
The atmosphere is 99.6% CO2

11. Global Carbon Cycle +7.9 per year Atmospheric CO2 + 3.2 per year 6.3
ppmv)
Fossil fuels
+ 3.2 per year
Photosynthesis
Land-use
Plant respiration
Soil respiration
6.3
1.6
Global
Carbon
Cycle
111 50 60 90 90 92
~1.4 Net flux ?
1.7 Net flux
Vegetation 610
Soils 1580
Ocean 39000
Stock = Billion metric tons
Flow = Billion metric tons per year

12. 2. Cycling (a) Pathways (b) Fluxes (in “Peta grams”, Pg = 1015 g
= “gigaton” = billion metric tons)
1015 g/year
(i) Photosynthesis =
(ii) Respiration = +110
(iii) Net Ocean Uptake =
(iv) Fossil Fuels =
(v) Biomass Burning =

13. (c) Mass Balance (of the atmosphere)
Net change = Input + Output + Internal Change
3.2 = ( ) + ( ) + 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?

14. 3. Controls
(a) Volcanic Activity
(b) Weathering
(c) Human influence

15. Volcanic Activity has a Strong Influence on
Atmospheric CO2 over Long Periods of Time

16. Over Short Periods of Time, Volcanic Activity has a Weak Influence on Atmospheric CO2
Volcanic Emissions = Pg C /yr
Anthropogenic emissions = 8 Pg C /yr
Therefore, human influences are ~160 times more important than volcanoes today.

17. 2. Weathering Reactions Control CO2 in the Atmosphere over Geologic Time

18. Human Influence on Atmospheric CO2
Increasing trend is modified by seasonal cycle of plant production in the Northern Hemisphere
Respiration
Photosynthetic uptake

19. CO2 Emissions from Fossil Fuels and Land Use Change

20. Projected CO2 Emissions will Increase - Tied to Population Growth -

21. Projected Changes in Annual Temperatures for the 2050s
Although regional patterns are not projected with high confidence,
land areas are projected to warm more than the oceans,
higher latitude regions (regions closer to the poles) are expected to warm more than equatorial regions, and
the Northern hemisphere is projected to warm more than the Southern hemisphere.
Projected change compared to the present, assuming ~1%/yr increase in equivalent CO2
Source: The Met Office. Hadley Center for Climate Prediction and Research

22. Temperature Projections
Global average temperature is projected to increase by 2.5° to 10.4°F from 1990 to 2100
Projected rate of warming is unprecedented for last 10,000 years
Temperature Projections
The global average surface temperature is projected to increase by 2.5 to 10.4°F (1.4 to 5.8°C) over the period 1990 to These results span the full range of scenarios used in the TAR (35 SRES scenarios).
The projected temperature increases are greater than those in the SAR (top end of the range is nearly doubled), which were 1.8 to 6.3°F (1.0 to 3.5°C). The revised higher estimates of projected warming are due primarily to the lower projected sulphur dioxide emissions in the TAR scenarios relative to the SAR scenarios (less of a cooling effect); i.e., a result of the assumption that we will produce fewer pollutants when producing electricity.
The projected rate of warming is much larger than the observed changes during the 20th century and is very likely to be unprecedented for at least the last 10,000 years. The magnitude of the warming at the upper end of the range is of the same order as the warming the earth experienced emerging from the depth of the last ice age 20,000 years ago to the warmth of the present interglacial beginning about 10,000 years ago.

23. How do we solve problems associated with our altered C cycle and increasing CO2 in the atmosphere?
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!
Carbon Sequestration – can something as simple as planting trees be the solution?

24. Can’t we just plant a bunch of trees?
CO2 uptake = 40 CO2 (with 1 N)
Net atm change
= (20 – 40) = -20
+20 CO2
Plant C:N = 40
20 CO2
OM decomposition
Soil C:N = 20
1 N

25. “There are no magic fixes for the CO2 problem”
Take-home message:
“There are no magic fixes for the CO2 problem”