Nitrous Oxide and Climate

TL;DR

This paper explains that nitrous oxide's contribution to global warming is relatively small compared to CO2, and restrictions on N2O emissions are unjustified and could harm food security.

Contribution

It provides a detailed analysis of N2O's radiative forcing and argues that restricting N2O emissions is not justified based on its minimal impact on climate change.

Findings

N2O's radiative forcing per molecule is 230 times that of CO2.

The increase rate of N2O is much slower than CO2, leading to a smaller overall warming contribution.

Restricting N2O emissions could harm global food supplies without significant climate benefits.

Abstract

Higher concentrations of atmospheric nitrous oxide (N2O) are expected to slightly warm Earth's surface because of increases in radiative forcing. Radiative forcing is the difference in the net upward thermal radiation flux from the Earth through a transparent atmosphere and radiation through an otherwise identical atmosphere with greenhouse gases. Radiative forcing, normally measured in W/m^2, depends on latitude, longitude and altitude, but it is often quoted for the tropopause, about 11 km of altitude for temperate latitudes, or for the top of the atmosphere at around 90 km. 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 (CO2) 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 greenhouse gas N2O. But the rate of increase of CO2 molecules, about 2.5 ppm/year (ppm = part per million by mole), is about 3000 times larger than the rate of increase of N2O molecules, which has held steady at around 0.00085 ppm/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 C/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. Proposals to place harsh restrictions on nitrous oxide emissions because of warming fears are not justified by these facts. Restrictions would cause serious harm; for example, by jeopardizing world food supplies.