North America in the Global Carbon Cycle What is the role of North America in the emissions of fossil fuel CO 2 ? What will future trends be? What is the role of North American vegetation in the global carbon cycle? Why do we think there is a vegetation sink, and what may the course be in the future? How can we understand and monitor North American sources and sinks of CO 2 and CH 4 ?

The heavier temperature lines 160,000 BP to present reflect more data points for this time period, not necessarily greater temperature variability. Climate and Atmospheric History of the past 420,000 years from the Vostok Ice Core, Antarctica, by Petit J.R., Jouzel J., Raynaud D., Barkov N.I., Barnola J.M., Basile I., Bender M., Chappellaz J., Davis J. Delaygue G., Delmotte M. Kotlyakov V.M., Legrand M., Lipenkov V.M., Lorius C., Pépin L., Ritz C., Saltzman E., Stievenard M., Nature, 3 June Antarctic Ice Core Data

Global CO 2 cycle

Year Historical consumption of fossil fuels. Emissions have increased by 2X since 1970, but there has not been a corresponding rise in the annual increment of CO 2. In 1970 ~75% of the emitted CO 2 stayed in the atmosphere, but only ~40% in Global Fuel Use 7800 in 2005!

CO 2 Airborne Fraction Starting year RECENT GROWTH IN ATMOSPHERIC CO 2 CONCENTRATIONS The average annual increase did not change much between 1970 and 2000, despite significant increases in fossil fuel emissions. Average rate of increase per year, 1.5 ppm = 3.25 x 10 9 tons/yr—little change (some variations) since 1975, but possibly starting to rise by 2005.

(Manning and Keeling et al., 2006) Changes in oxygen track the role of the land vegetation vs. ocean uptake of anthropogenic CO 2. Land uptake may have decreased at the end of the 1990s, after having increased in the early 1990s.

Fossil Fuel+ cement5.3 Tropical Deforestation1-2 Total Global CO 2 budget (PgC yr -1 ) 1980 – – 2000 Sources Atmospheric accumulation 3.2 Ocean uptake2.1 "Missing Sink"1-2 Total Sinks 2.1 Pg C = 1 ppm atmospheric CO 2 [source: Cias et al., Science 269, 1098, (1995)]  Is this budget accurate? What is the scientific basis for these numbers?  Why should mid-latitude terrestrial plants absorb anthropogenic CO 2 ? When did this uptake begin, can/will it continue?  What are the implications of terrestrial uptake for  Future CO 2 ?  US policy?  Climate change?

The ocean’s capacity to take up CO 2 will diminish with time, as the pH of the ocean declines due to uptake of CO 2. The ocean becomes acidified. Uptake of CO 2 by chemical dissolution is limited by the rate for exchange between deep ocean water and surface water, and eventually, by acidification of the oceans. Acidification of the ocean is likely to lead to major shifts in marine ecosystems. Atmospheric release of CO 2 from burning of fossil fuels will likely give rise to a marked increase in ocean acidity, as shown in this figure. ( upper ) Atmospheric CO 2 emissions and concentrations, historical (—) and predicted (---), together with changes in ocean p H based on mean chemistry. The emission scenario is based on the mid-range IS92a emission scenario assuming that emissions continue until fossil fuel reserves decline =25% = 5 (!) increase in [H + ].

Regional ocean- and land-atmosphere CO 2 fluxes, 1992–1996. Orange: Bottom-up land- atm. flux [Pacala, et al., 2001; Kurz and Apps, 1999 N. America; Janssens, et al., 2003, Europe; (Shvidenko and Nilsson, 2003; Fang, et al., 2001, for North Asia]; Cyan: Bottom-up ocean fluxes (Takahashi, et al., 2002), Blue = ocean-atmosphere fluxes, inverse models, Green = land-atmosphere fluxes, inverse models, Magenta = land plus ocean inversion fluxes, Red: fossil fuel emissions, subtracted from net. Source: P. Ciais, 2006

Uptake of CO 2 in the US (PgC yr -1 ) [Pacala et al., 2001] US "forests": Net sink: PgC yr -1 Emissions (1996): US 1.44 Mexico 0.09 Canada 0.11 Forests in the US – and many other places – are in middle to young age classes (25-75 years), due to changes in agriculture (intensification) and forest management (intensification).

NH % of land area in forests Year MA Fitzjarrald et al., 2001 A legacy: land use change in New England

Aboveground woody biomass (MgCha -1 ) oak other spp Year Rates for growth and for carbon uptake are accelerating in this 80- year-old New England Forest…why is that? Will that continue? How big do North American trees grow?

cm Changing climate and C: an example from NOBS flux site, Thompson, MB Snow cover Temperature PEAT 45% cover

Deviation from the 9-year means of annual Net Ecosystem Exchange ( upper, g C m -2 ), temperature ( middle, C), and two-year precipitation sums ( lower, cm), illustrating the critical role hydrology plays in determining the annual carbon balance at a mature black spruce forest. P2 (mm/2yr) NEE (kgC/ha/yr) r 2 =.72 p<.0035 slope=-3.5 Precipitation (mm in 2 yr) (gC m -2 yr -1) Uptake | emission Annual NEP, Thompson, MB T : warmer Precip: wetter Water table depth and hydrology are key factors controlling the accumulation or ablation of peat Year Net CO 2 echange Annual T anomaly ( o C) Annual Precip Anom (mm)

Daily respiration, g C m -2 Water table depth, cm Figure 2: interaction of WT depth and CO 2 Flux from the boreal peatland in Manitoba, summer 2002

But wasn't the weather unusually cold in ? Not over the globe…. [base yrs: ]

Correlation: {  T,  soil moisture index} CCSM1-Carbon Control Simulation DJFJJA Positive correlation  warmer-wetter; or cooler-drier Negative correlation  warmer-drier; or cooler-wetter slide courtesy Inez Fung [ I. Fung, S. Doney, et al.]]

Summary The North American Carbon Program will: measure the large sink for fossil fuel CO 2 that appears to be operating in the region determine why this sink exists, and define the controlling factors (temperature, precipitation, legacies, CO 2, nutrients, …) quantitatively. enable projections of future trajectories support decision makers in dealing with key global change issues through management and policy options.