Nitrous Oxide and Climate

Higher concentrations of atmospheric nitrous oxide are expected to slightly warm Earth's surface because of an increase in radiative forcing.  For current concentrations of greenhouse gases, the radiative forcing per added N₂O molecule, is about 230 times larger than the forcing per added carbon dioxide molecule.  This is due to the heavy saturation of the absorption band of the relatively abundant greenhouse gas, CO₂, compared to the much smaller saturation of the absorption bands of the trace greenhosue gas N₂O_.  But the rate of increase of CO₂ molecules, about 2.5 ppm/year is about 3000 times larger than the rate of increase of N₂O molecules, which has held steady at around 0.85 ppb/year since 1985.  So the contribution of nitrous oxide to the annual increase in forcing is 230/3000 or about 1/13 that of CO₂.  If the main greenhouse gases, CO₂, CH₄ and N₂O have contributed about 0.1 K/decade of the warming observed over the past few decades, this would correspond to about 0.00064 K per year or 0.064 K per century of warming from N₂O.  This rather small warming does not support placing harsh restrictions on nitrous oxide emissions, which could seriously jeopardize world food supplies.