The effect of carbon-nitrogen coupling on the reduced land carbon sink caused by tropospheric ozone



[1] Tropospheric ozone is known to have a damaging effect on carbon uptake in the terrestrial biosphere. We show that limitations of available nitrogen for sufficient plant growth reduce the negative impact of tropospheric ozone on carbon uptake in plants, leading to a smaller indirect change in radiative forcing than previously calculated. Transient climate simulations between 1900 and 2004 where plant growth is affected by tropospheric ozone have been performed by the National Center for Atmospheric Research Community Land Model with and without a coupling to the nitrogen cycle. When the land model includes nitrogen limitation on plant growth, the negative effect from tropospheric ozone on carbon uptake in plants is reduced by up to a factor of four compared to model simulation without nitrogen limitation. Only 2–5% of the radiative forcing from CO2 between 1900 and 2004 can be attributed to the indirect effect of tropospheric ozone which is a factor of six lower than results from previous studies.