Bomb Radiocarbon Evidence for Strong Global Carbon Uptake and Turnover in Terrestrial Vegetation

The Science

Atmospheric bomb testing in the 1960s roughly doubled the amount of radiocarbon in the atmosphere. Agreements to limit testing led to an abrupt stopping of bomb testing, and as a result, the subsequent decline of radiocarbon in the atmosphere provided a global constraint on plant growth, which removed radiocarbon from the atmosphere. A team of researchers compared observations and models of the carbon cycle to show model estimates of plant growth are too low, and carbon plants must be cycling more quickly than current models estimate.

The Impact

Models of the global carbon cycle and climate system are needed to understand how emissions of carbon dioxide will affect climate. Benchmarks of the global carbon cycle such as from radiocarbon allow a constraint on the rates of carbon moving between the atmosphere and biosphere. Because observations suggest plant growth rates are too low in current models, these results will provide better constraints on global models and lead to more accurate climate projections.

Summary

A team of researchers compared observed and modeled radiocarbon accumulation in the global biosphere to understand how observations during the immediate period after widespread aboveground bomb testing could constrain growth rates of plants and associated uptake of radiocarbon in plant tissues. This comparison included models with a dedicated representation of radiocarbon, as well as building emulators for models without explicit treatment of radiocarbon.

Modeled radiocarbon uptake rates were much lower than observations, suggesting a strong bias in modeled carbon cycling. Because models agree well with total biomass observations, this too-low growth also implies a too-low rate of turnover of plant tissues, possibly because plants allocate more carbon to short-lived tissues or fast-growing trees tend to die more quickly than slow-growing trees.

Principal Investigator

Charlie Koven
Lawrence Berkeley National Laboratory
[email protected]

Program Manager

Brian Benscoter
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

Support was received from the Environmental System Science program through the Next-Generation Ecosystem Experiments Tropics (NGEE Tropics) as well as the Reducing Uncertainties in Biogeochemical Interactions through Synthesis and Computation (RUBISCO) Science Focus Area within the Regional and Global Model Analysis program area of the U.S. Department of Energy’s Biological and Environmental Research program.

References