A facile comparison: the problem with CO2 involves the equilibrium level (or lack thereof) between the flows of what is emitted to the pool versus removed.
In contrast, excessive bio-available nitrogen is unlikely to build up, not when most of the biosphere is waiting to grab it and (relatively quickly) turn it back into inert N2 gas.
In contrast, excessive bio-available nitrogen is unlikely to build up, not when most of the biosphere is waiting to grab it and (relatively quickly) turn it back into inert N2 gas.