Biogeosci. 6, 2099–2120 (2009)
Global climate simulations have traditionally assumed that limitless nutrients are available for new plant growth, which can temper warming by absorbing CO2 from the atmosphere. New research now questions that assumption and suggests that warming over the next century could be higher than anticipated.
The new study, by Peter Thornton of Oak Ridge National Laboratory, Tennessee, and colleagues, is the first to successfully incorporate the nitrogen cycle and its interactions with the carbon cycle into a fully coupled global climate model — that is, one that includes the ocean and the atmosphere. Simulating the climate over 230 years, the researchers found that, compared with a regular simulation, carbon taken up by terrestrial plants was two to three times lower in a high-CO2 world owing to nitrogen-imposed restrictions on plant growth. But warmer temperatures also encouraged decomposition, freeing up nitrogen in the soil and increasing carbon uptake. This latter effect was insufficient to offset nutrient limitations on plant growth, however, resulting in an overall reduction in new vegetation.
The authors suggest that inclusion of the nitrogen cycle in other climate models would narrow the uncertainty in estimates of future carbon dioxide concentrations.