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Scientists Integrate Nitrogen Cycle into Climate Model; Results Suggests Atmospheric CO2 Concentrations May End Up Higher Than Expected

Schematic illustrating feedback pathways coupling terrestrial carbon and nitrogen cycles in the integrated model. Blue arrows show, in general, the processes represented in previous carbon-only land model components. Orange arrows show the additional processes represented in the coupled carbon-nitrogen land model, differentiated here between rapid internal cycling (solid arrows), and slower fluxes between land pools, the atmosphere, and ground water (dashed arrows). Source: Thornton et al. (2009)

A team of climate scientists from eight US national labs and academic institutions have successfully incorporated the nitrogen cycle into global simulations for climate change for the first time, questioning previous assumptions regarding carbon feedback and potentially helping to refine model forecasts about global warming.

The results illustrate the complexity of climate modeling by demonstrating how natural processes still have a strong effect on the carbon cycle and climate simulations. In this case, scientists found that the rate of climate change over the next century could be higher than previously anticipated when the requirement of plant nutrients are included in the climate model.

The study, by scientists from institutions including the US Department of Energy’s (DOE) Oak Ridge National Laboratory (ORNL); the National Center for Atmospheric Research (NCAR); the National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory (ESRL); Woods Hole Oceanographic Institution; UC Irvine; Cornell University; UC Berkeley; and the University of Kansas, was published 8 October in Biogeosciences, an interactive open access journal of the European Geosciences Union.

Inclusion of fundamental ecological interactions between carbon and nitrogen cycles in the land component of an atmosphere-ocean general circulation model (AOGCM) leads to decreased carbon uptake associated with CO2 fertilization, and increased carbon uptake associated with warming of the climate system. The balance of these two opposing effects is to reduce the fraction of anthropogenic CO2 predicted to be sequestered in land ecosystems.

—Thornton et al. (2009)

To date, climate models have ignored the nutrient requirements for new vegetation growth, assuming that all plants on earth had access to as much nutrient flow as needed. By taking the natural demand for nutrients into account, the authors have shown that the stimulation of plant growth over the coming century may be two to three times smaller than previously predicted.

However, this reduction in growth is partially offset by another effect on the nitrogen cycle: an increase in the availability of nutrients resulting from an accelerated rate of decomposition of dead plants and other organic matter that occurs with a rise in temperature.

Combining these two effects, the authors discovered that the increased availability of nutrients from more rapid decomposition did not counterbalance the reduced level of plant growth calculated by natural nutrient limitations; therefore less new growth and higher atmospheric CO2 concentrations are expected.

...we note that the present simulations have not included the influence of disturbance history and land use. These factors have been shown to interact strongly with C-N dynamics. We are currently exploring these interactions in the context of the fully-coupled climate system model, and we expect that these interactions will result in larger values of atmospheric CO2 concentration than predicted here.

—Thornton et al. (2009)

ORNL’s Peter Thornton, lead author of the paper, describes the inclusion of these processes as a necessary step to improve the accuracy of climate change assessments.

We’ve shown that if all of the global modeling groups were to include some kind of nutrient dynamics, the range of model predictions would shrink because of the constraining effects of the carbon nutrient limitations, even though it’s a more complex model.

—Peter Thornton

The inclusion of the nitrogen cycle marks one more step toward a more realistic prediction for the future of the earth’s climate. Nevertheless, potentially significant processes and dynamics are still missing from the simulations. Thornton also stresses the importance of long-term observation so scientists can better understand and model these processes.

A 15-year study of the role nitrogen plays in plant nutrition at Harvard Forest was an important observational source used to test their mathematical representation of the nitrogen cycle—a long experiment by any standards, but still an experiment that, according to Thornton, could improve the accuracy of the simulation if conducted even longer.

Other shortcomings of climate simulations include the disregard of changing vegetation patterns due to human land use and potential shifts in types of vegetation that might occur under a changing climate, although both topics are the focus of ongoing studies.

The research was funded by the DOE Office of Science. Additional resources were contributed by NASA Earth Science Enterprise, Terrestrial Ecology Program; National Center for Atmospheric Research through the NCAR Community Climate System Modeling program and the NCAR Biogeosciences program.



Henry Gibson

The efforts to reduce CO2 increases to the air must logically include the limitation of a nations population. Besides the obvious use of fuel in nations with large populations, there is the highly ignored fact that all humans release CO2 by eating food. Many people have been induced to falsely believe that food is carbon neutral, but they and those that mislead them forget that food and other plant growth can be made carbon negative by putting the materials in permanent storage instead of eating it or burning it. Most food and bio-fuel supplies also now rely upon fossil fuels.

Nuclear or solar energy can be used to remove all carbon from food and other biomass and make big piles of it. This was obviously done in the past by plants, algae, bacteria and geological forces.

Biomass is now much used by organisms in the soil to produce nitrates from the air that allow for more rapid growth of plant material that takes up even more CO2 from the air which produces even more plant material for more CO2 capture. Where water and minerals, such as phosphorous and radioactive potassium, are available in sufficient quantities the growth and sequestation of carbon can be unlimited. Removal of the biomass from the area reduces the energy available for carbon fixation and the minerals needed for growth. It is known that massive growth of plants in the ocean is limited in some places by the lack of iron.

Even in Hawaii the growth of pineapples was limited on the iron containing soil because the iron was in the wrong form. Automobiles had to be dissolved in acid to provide the iron needed. Certain soil bacteria might be found to combine with the nitrogen bacteria to get the iron from the volcanic rock. Relatives of lichens are a possibility. ..HG..


Great, more abortions are needed and a tax on flatulence.


A lot of the nitrogen fertilizer is made by using natural gas. They get the hydrogen to get the nitrogen to make the ammonia to make the nitrogen fertilizer.

I would say that a lot of the CO2 created in the process is just vented to the atmosphere and all this is done for the sake of crop yields. They could capture the CO2 to be used for other purposes, but probably do not because it is not "cost effective". (why bother)

Biomass can be used to do the same thing and is more CO2 neutral. The carbon left from gasification can be returned to the soil. Or you could leave the biomass in the field to rot and outgas methane, which is more than 20 times more potent a green house gas than CO2.



How about a xx% tax on red meat, bacon, eggs and ice creams; but an equivalent $$$ tax credit on chicken meat, cereals, vegetables, fruits, nuts, olive oil and fish.

People would be leaner, weight less, move easier, be healthier, have less cancers, less diabetes, etc and millions of acres could be liberated for agrofuel culture or to feed the one billion people that do not have enough to eat.

Dont forget that the average red meat takes 11+ times the proteins to produce than it gives out. Chicken is less than 3 times. Eating grains and vegetables directly is even more efficient.

For efficiency sake, we should all be vegetarians and lose up to 50% body weight. A car with for lean passengers, i.e. 2 males and 2 females = ( 4 x 125 lbs = 500 lbs) would go much further on 1 Kwh than the same car with 4 fat passengers ( 4 x 250 lbs = 1000 lbs). The weight savings could make room for 2 more battery packs.

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Where water and minerals, such as phosphorous and radioactive potassium, are available in sufficient quantities the growth and sequestation of carbon can be unlimited. Removal of the biomass from the area reduces the energy available for carbon fixation and the minerals needed for growth.

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