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 (bottom) Past 1000 years, N. Hemisphere only The “Hockey Stick” of change

Greenhouse gas increases are driving temperature rise ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_mm_mlo.txt

The rate of CO 2 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 CO 2, CH 4, N 2 O 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 forcing Models 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, IPCC Summary statements from the 4 th 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 , 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.” "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 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 CO 2 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 (x g C) Rocks 65,000,000 Oceans 39,000 Soils 1,580 Atmosphere 860 Land Plants 610 Carbon Forms include: Inorganic C (e.g., HCO 3 - ) Organic C (e.g., CHO compounds) Gases (CO 2, CH 4, CO) The carbon in the atmosphere is 99.6% CO 2

Atmospheric CO ppmv) Vegetation 610 Soils Ocean Stock = Billion metric tons Flow = Billion metric tons per year Global Carbon Carbon Cycle Cycle per year ~1.4 Net flux +7.9 per year ~1.7 Net flux River Transport

2. Cycling (a) Pathways (previous slide) (in “Peta grams”, Pg = g (b) Fluxes (in “Peta grams”, Pg = g = “gigaton” = billion metric tons) = “gigaton” = billion metric tons) g/year (i) Photosynthesis = (ii) Respiration = (iii) Net Ocean Uptake = (iv) Fossil Fuels = +6.3 (v) Biomass Burning = +1.6

(c) Mass Balance (of the atmosphere) Net change = Input + Output + Internal Change 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 CO 2 over Long Periods of Time

Over Short Periods of Time, Volcanic Activity has a Weak Influence on Atmospheric CO 2 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 CO 2 in the Atmosphere over long Geologic Time

Respiration Photosynthetic uptake N. Hemisphere S. Hemisphere (c) Biological controls – affect seasonal patterns Global distribution of CO

Projected CO 2 Emissions will be tied to Population Growth (d) Human Influence – CO 2 emissions from fossil fuels and land-use change

Model predictions 95% confidence intervals (uncertainty) Projected Changes in Annual Temperatures for 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 CO 2 C:Fe = 106: Carbon Sequestration – can something as simple as planting trees be the solution? How do we solve problems associated with our altered C cycle and increasing CO 2 in the atmosphere? C:N:P:Fe (!) Element cycles interact!

Can’t we just plant a bunch of trees? CO 2 uptake = 50 CO 2 (with 1 N) Plant C:N = 50 Soil C:N = 25 OM decomposition 25 CO 2 1 N +25 CO 2 Net atm change = (25 – 50) = -25

Take-home message: “There are no magic fixes for the CO 2 problem”

Summary: 1.The global carbon cycle is closely tied to Earth’s temperature through carbon-based greenhouse gases (CO 2 and CH 4 ). 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 CO 2 increases, in part because element cycles (C, N, P, Fe) are linked and interact.