About the actual radiative impact of greenhouse gas emission over time

Question

Say we will emit a certain amount of greenhouse gas over the next 50 years (e.g. 100 billion tons CO2-eq in total). What would happen if I implement a certain GHG mitigation effort to cut the same amount of GHG (say sequester 20 billion tons CO2-eq) in the early years (e.g. year 0-10) vs in later years (year 40-50)?

I would imagine that cutting the gas earlier would be better since overall global warming is a cascade of positive feedbacks? A bunch of other similar questions can be asked like cutting the same amount of GHG over first 10 years (but no cutting thereafter) vs spread out the cutting to the entire 50 years. What are some major consideration to look at? Is it generally better to cut GHG as early as possible?

Answer 1

There is no doubt that the sooner the mitigation effort happens, the greater will be its impact.

In other words, the impact on year 2100 climate of the sequestration of 20 billion tons $\ce{CO2}$-eq right now, is much bigger than the impact that the same action will have in 30 years from now. Therefore, a mitigation action today is much cheaper than one done in the future but with equal impact on year 2100 climate (assuming no dramatic changes in the sequestration technology).

This is due to the long lifetime of $\ce{CO2}$ in the atmosphere, that is usually estimated to be longer than a few centuries. Although, some sources place the lower limit at around 30 years, its lifetime is most likely longer than 50 years.

This means that any $\ce{CO2}$ that is not captured today (or emitted), will remain in the atmosphere trapping heat and rising Earth's temperature until year 2100 and beyond.