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 Surface TemperaturTemperature Variatione Variation(top) Past 140 (top) Past 140 years, globalyears, global

(bottom) Past (bottom) Past 1000 years, N. 1000 years, N. Hemisphere Hemisphere onlyonly

The “Hockey Stick” of change

Greenhouse gas increases are driving temperature riseGreenhouse gas increases are driving temperature rise

ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_mm_mlo.txt

The rate of COThe rate of CO22 increase is accelerating increase is accelerating

ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_mm_mlo.txt

Source: IPCC TAR 2001

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”

Human-caused

greenhouse gas

increases have

warmed the world

Observations IPCC 2007: WG1-AR4

Models using only natural forcingModels using both natural and human forcing

Global and Continental Climate Change – observations and models

“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.”

“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.”

“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.”

Intergovernmental Panel on Climate Change, IPCCSummary statements from the 4th Assessment Report, 2007

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.htmlhttp://www.whitehouse.gov/news/releases/2007/02/20070207-5.html

"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.

Scientists must support themselves financially, and the hyping of global warming leads to more research grants.

Beware the Arguments and Ploys of Skeptics and Politicians

1. Personal or professional gain 2. Selective use of data (cherry-picking)1.

2.

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 ploy of “cherry-picking data”

1992“Rio”

1997“Kyoto”

2001“9/11 recession”

+15%

-1%

The COThe CO22 concentration in the atmosphere is strongly concentration in the atmosphere is strongly correlated with the Earth’s surface temperaturecorrelated with the Earth’s surface temperaturebut, there are aspects of the carbon cycle that we don’t but, there are aspects of the carbon cycle that we don’t

understand…understand…

Understanding Global Element Cycles

A Method of analysis:

1. Accounting2. Cycling and Pathways3. Controls

(This method applies to all element cycles)

The Global Carbon The Global Carbon CycleCycle

1. Accounting (x 10(x 101515 g C) g C)

Rocks 65,000,000Oceans 39,000Soils 1,580Atmosphere 860Land Plants 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

Atmospheric CO2860 ( @ 385 ppmv)

Vegetation 610Soils 1580

909050

Ocean 39000

6.3

1.6

60

Stock = Billion metric tonsFlow = Billion metric tons per year

GlobalGlobal CarbonCarbon CycleCycle11

1

92

+ 3.2 per year

~1.4 Net flux

+7.9 per year

~1.7 Net flux River Transport

2. Cycling

(a) Pathways (previous slide)

(b) Fluxes (in “Peta grams”, Pg = 10(in “Peta grams”, Pg = 101515 g g

= “gigaton” = billion metric = “gigaton” = billion metric tons)tons)

10101515 g/year g/year(i) Photosynthesis = - 111(ii) Respiration = + 110(iii) Net Ocean Uptake = -

1.7 (iv) Fossil Fuels = +6.3

(v) Biomass Burning = +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 “* Need a “sinksink” of (5.2 – 3.2) = 2.0 Pg C / ” of (5.2 – 3.2) = 2.0 Pg C /

year to balance the global C budget. year to balance the global C budget.

Where is the sink?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) WeatheringStrong controls over long periods of time, Weak controls

over short periods of time.

(c) Biological controlsStrong 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 (a) Volcanic Activity has a Strong Influence on Atmospheric COAtmospheric CO22 over over Long PeriodsLong Periods of Time of Time

Over Over Short PeriodsShort Periods of Time, of Time, Volcanic Activity has a Weak Volcanic Activity has a Weak

Influence on Atmospheric COInfluence on Atmospheric CO22

• 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 (b) Weathering Reactions Control COCO22 in the Atmosphere over long in the Atmosphere over long

Geologic TimeGeologic Time

Respiration

Photosynthetic uptake

N. Hemisphere

S. Hemisphere

(c) Biological controls – affect seasonal (c) Biological controls – affect seasonal patternspatterns

Global distribution of CO2 1992-2001

Projected CO2 Emissions will

be tied to Population

Growth

(d) Human Influence – CO(d) Human Influence – CO22 emissions from fossil emissions from fossil fuels and land-use changefuels and land-use change

Model predictions95% confidence intervals (uncertainty)

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.

From IPCC 2007

Deg C

Dec, Jan, Feb

1. The “Geritol Fix” – adding Fe to the Southern Oceans to stimulate algae to take up more CO2

C:Fe = 106:0.01

2. Carbon Sequestration – can something as simple as planting trees be the solution?

How do we solve problems associated with How do we solve problems associated with our altered C cycle and increasing COour altered C cycle and increasing CO22 in in

the atmosphere?the atmosphere?

C:N:P:Fe (!) Element cycles interact!

Can’t we just plant a bunch of trees?

CO2 uptake = 50 CO2 (with 1 N)

Plant C:N = 50

Soil C:N = 25OM decomposition

25 CO2

1 N

+25 CO2

Net atm change = (25 – 50) = -25

Take-home message:Take-home message:

““There are no magic There are no magic fixes for the COfixes for the CO22 problem”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.