cades through the decomposition of wood or soil organic matter. Here we identify “equilibration” of the nitrogen budget with water/energy and carbon fluxes as an additional process causing decadal and longer time scale behavior.

Just as perturbations to the climate system can cause the nitrogen and carbon systems to respond ( 4 , 24 ), perturbations of the N inputs from air pollution or fertilization will also cause long-lived ecosystem changes ( 34 , 36 , 44 ). Analyses of the past interannual variability of the carbon cycle, and of its potential future behavior, must consider mechanisms that act through the coupled water/energy, carbon, and nitrogen cycles.

We acknowledge the assistance of Rebecca McKeown, Melannie Hartmann, and Hank Fisher with conducting and analyzing global Century runs, with special thanks to Becky for her exceptional effort in completing the global calculations for this paper. Dennis Ojima, Beth Holland, Alan Townsend, and Jason Neff all helped conceive of or design the model experiments. This research was supported by the National Aeronautics and Space Administration Earth Observing System Interdisciplinary Science Program, and by the National Center for Atmospheric Research. The National Center for Atmospheric Research is sponsored by the National Science Foundation.

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Contents (R1-R4)

Climate change and carbon dioxide: An introduction (1-2)

Tribute to Roger Revelle and his contribution to studies of carbon dioxide and climate change (3-7)

Equilibration of the terrestrial water, nitrogen, and carbon cycles (8-11)

Potential responses of soil organic carbon to global environmental change (12-19)

Global air-sea flux of CO2: An estimate based on measurements of sea-air pCO2 differences (20-27)

Characteristics of the deep ocean carbon system during the past 150,000 years: CO2 distributions, deep water flow patterns, and abrupt climate change (28-35)

Direct observation of the oceanic CO2 increase revisited (36-41)

The observed global warming record: What does it tell us? (42-48)

Possible forcing of global temperature by the oceanic tides (49-56)

Spectrum of 100-kyr glacial cycle: Orbital inclination, not eccentricity (57-62)

Can increasing carbon dioxide cause climate change? (63-70)

Gases in ice cores (71-77)

Tree rings, carbon dioxide, and climatic change (78-81)

Geochemistry of corals: Proxies of past ocean chemistry, ocean circulation, and climate (82-89)

A long marine history of carbon cycle modulation by orgital-climatic changes (90-97)

Dependence of global temperatures on atmospheric CO2 and solar irradiance (98-107)