Pacific Northwest ecosystem responses to atmospheric changes in the 21st century

The terrestrial carbon cycle regulates carbon pools and fluxes throughout the Earth system. Currently, the Pacific Northwest is a carbon sink; it is gaining more carbon than it is releasing into the atmosphere. Investigating changes to this carbon sink is critical for understanding ecosystem responses to future environmental change. The Community Land Model version 4 (CLM4CN) was run with eight simulations for varying atmospheric changes. Half of the simulations ran using Qian climate data for 1948-2004, and half ran with climate data for 2075-2100 from the Representative Concentration Pathways 8.5 scenario (RCP8.5). One run from each group was forced with an increased carbon dioxide (CO2) concentration of 937.87 parts per million (ppm), another was forced with an increased tropospheric ozone (O3) concentration, the third included a combination of increased O3 and CO2 concentrations, and the fourth was a control. Carbon pools decreased with the RCP8.5 scenario in all simulations. An increased CO2 concentration grew carbon pools in both climates. An increased O3 concentration had the opposite effect. A combination of O3 and CO2 showed that carbon pools increased, and the increase was smaller than with CO2 alone. Net primary production (NPP) and net ecosystem production (NEP) mirrored the carbon pool changes. Net ecosystem exchange (NEE) showed that an increased CO2 concentration increased the carbon sink in both climates. The region became a source of carbon with increased O3. The carbon sink increased with a combination of O3 and CO2, with the increase being smaller than the CO2 alone. The figure shows the changes in the ecosystem carbon pool resulting from increasing gas concentrations in various simulations. The x axis represents the future climate scenario control. The black box represents the difference between the carbon pool with increased carbon dioxide (CO2) and the control simulation. The grey box is the difference in the carbon pool between the simulation with increased ozone (O3) and the control simulation. The white box is the carbon pool difference between the simulation with a combination of both gases and the control simulation. There is carbon pool growth for increased CO2 (black box), growth for an increase in both O3 and CO2 (white box), and a decrease for increased O3 (grey box).