The Ocean Uptake of CO2 is an Incredibly Loose Cannon!

Barry Huebert
NCAR-EOL Affiliate Scientist
University of Hawaii Professor of Oceanography
huebert@hawaii.edu

While present and past CO₂ budgets are very well constrained by observed atmospheric increases, isotopic measurements, and highly accurate O₂ measurements, the future CO₂ budget is far less certain. Studies of paleo variability are of limited use in forecasting, since we are already at CO₂ concentrations far above any the inhabited Earth has experienced.

For predictions of future ocean CO₂ uptake we must use F = Vt Δp CO₂ where F is the air-sea flux, Vt is an exchange velocity, and Δp CO₂ is the concentration (actually, fugacity) difference across the interface. Existing models of Vt are uncertain to at least a factor of two and depend in unknown ways on factors including wind, surfactant films, wave characteristics, and bubbles, among others. Our ignorance of the quantitative controls on Vt propagate to an alarming uncertainty in the future increase rate of atmospheric CO₂. Inversion models that rely on wind-only exchange velocity models are similarly uncertain. There are things that could be done to improve on this situation.

The IPCC chose not to examine the role of ocean CO₂ uptake uncertainty in its Fourth Assessment.