Simple climate model

One tonne of carbon sequestered can offset the radiative forcing of a continuous emission of 0.04 kg nitrous oxide per year over 500 years.

“In other words, a one-off sequestration of one t of C would offset the RF of a continuous emission of 0.1 kg N2O per year over 100 years or 0.04 kg N2O per year over 500 years.”

The radiative forcing of a pulse emission of one tonne of CO2 decreases from 0.0017 in year one to 0.0007 nW m−2 in year 100, and 0.0005 nW m−2 in year 500.

“The RF of a pulse emission of one t of CO2, for example, decreases from 0.0017 in year one to 0.0007 nW m−2 in year 100, and 0.0005 nW m−2 in year 500.”

The radiative forcing of one tonne of CH4 drops from 0.2 nW m−2 in year one to 0.0003 nW m−2 in year 100 and 0.00005 nW m−2 in year 500.

“Meanwhile, the RF of one t of CH4, as a result of its relative short perturbation lifetime, drops drastically within a few decades (i.e., from 0.2 nW m−2 in year one to 0.0003 nW m−2 in year 100 and 0.00005 nW m−2 in year 500).”

The radiative forcing associated with a pulse emission of one tonne of N2O is 0.36 nW m−2 in year one and 0.005 nW m−2 in year 500.

“The RF associated with a pulse emission of one t of N2O gradually reduces over time and lasts for more than half a millennium (i.e., 0.36 nW m−2 in year one and 0.005 nW m−2 in year 500) (Fig. 1a).”

One tonne of carbon sequestered can offset the radiative forcing of a continuous emission of 0.99 kg methane per year over 100 years.

“Here, our analysis shows that one tonne of carbon sequestrated can offset radiative forcing of a continuous emission of 0.99 kg methane or 0.1 kg nitrous oxide per year over 100 years.”

One tonne of carbon sequestered can offset the radiative forcing of a continuous emission of 0.1 kg nitrous oxide per year over 100 years.

“Here, our analysis shows that one tonne of carbon sequestrated can offset radiative forcing of a continuous emission of 0.99 kg methane or 0.1 kg nitrous oxide per year over 100 years.”

One tonne of carbon sequestered can offset the global surface temperature change of a continuous emission of 1.05 kg methane per year over 100 years.

“In other words, a one-off sequestration of one t of C would offset the RF of a continuous emission of 0.99 kg CH4 per year or the global temperature change of 1.05 kg CH4 per year over 100 years.”

The result was estimated using a simple linearized climate model with the main purpose of giving a sense of orders of magnitude.

“Note that the result was estimated using the simple linearized climate model with a main purpose of giving a sense for orders of magnitude (see Discussion for the uncertainty of the model).”

The amount of CO2 that needs to be stored to compensate the climate impact of a continuous flow of one tonne of CH4 per year over 100 years is about 3.7 kt for radiative forcing and 3.5 kt for global surface temperature change.

“Given a 100-year timeframe, for example, the amount of CO2 that needs to be stored to compensate the climate impact of a continuous flow of CH4 (one t per year) equals about 3.7 kt for RF and 3.5 kt for global surface temperature change (Fig. 2).”

Because the climate benefits of CO2 removal fade away while the climate impacts of CH4 slightly increase, more carbon needs to be sequestered to offset continuous emissions over a longer timeframe.

“It is worth noting that while the climate benefits of CO2 removal fade away, the climate impacts of CH4 slightly increase (Fig. 1). This implies that more C needs to be sequestrated to offset continuous emissions over a longer timeframe (Fig. 2).”

The radiative forcing of a continuous flow of CO2 emissions increases practically indefinitely, while the radiative forcing of continuous flows of CH4 and N2O stabilizes with time.

“The RF of a continuous flow of CO2 emissions increases (practically) indefinitely, while the RF of a continuous flow of CH4 and N2O stabilize with time.”

Continuous emissions of CO2 add cumulatively to global temperature change.

“When expressed in global surface temperature change, it takes even more years for the impact of continuous CH4 and N2O emissions to find this new equilibrium but it still shows a trend towards stabilization, while continuous emissions of CO2 add cumulatively to global temperature change (Fig. 1d).”

The time to reach a new equilibrium for continuous emissions is a few decades for CH4 and more than 500 years for N2O.

“The longer the perturbation lifetime of the gas, the longer the time it takes to reach the new equilibrium (i.e., a few decades for CH4 and more than 500 years for N2O).”

It takes over 500 years for the temperature change from a pulse emission of CO2 to exceed that of an equal pulse emission of CH4.

“It is worth noting, though, that due to the inertia of the climate system it takes over 500 years for the temperature change from a pulse emission of CO2 to exceed that of an equal pulse emission of CH4, i.e., while the perturbation lifetime of CH4 is short, its resulting climate impacts are far from so.”

The conversion ratio between the radiative forcing benefits of one pulse of CO2 sequestration and the radiative forcing impact of a continuous flow of N2O emissions increases from 35 kt at year 100 to 87 kt at year 500.

“The conversion ratio between, for example, the RF benefits of one pulse of CO2 sequestration and the RF impact of a continuous flow of N2O emissions increases from 35 kt at year 100 to 87 kt at year 500 (Fig. 2).”