We had an interesting lunch colloquium on reactive nitrogen on Thursday here at ECN.
What I found most interesting is that it looks like reactive nitrogen actually cools the climate a little. In lifecycle analyses of biomass, emissions of N2O and indirect land use effects are sometimes made into huge bogeymen. Now, here I learn that reactive nitrogen (much of which = fertiliser) also enhances aerosol cooling and uptake of carbon in forests. These indirect effects of course don't make their way into lifecycle analyses that try to trash biofuels.