Which climate change mitigations take longer than 12 years to see a net benefit?

Question

The recent IPCC SR15 Report has garnered a lot of press coverage because it warns that we must dramatically reduce CO2 emissions by the year 2030, less than 12 years away.

Global net anthropogenic CO₂ emissions [must] decline by about 45% from 2010 levels by 2030 (40–60% interquartile range), reaching net zero around 2050 (2045–2055 interquartile range).

I would like to know which of the well-known and scalable emission mitigation strategies are still viable on such a short timeframe. Specifically, I am looking for answers in two categories:

1) Which emission mitigation strategies, if any, are unlikely to produce a net reduction in emissions within the 12 year timeframe? For example, early solar photovoltaic panels had an energy payback as high as 20 years, which would have made them non-viable on a 12 year timeframe. (Modern PV panels have a much faster payback, closer to 2 years.)

2) Which emission mitigation strategies, if any, are likely to cause a net reduction in emissions of greater than 45% within 12 years? In order to hit our target of 45% reduction by 2030 we will need a mix of techniques and technologies with varying payback. Which solutions are able to beat the target in this short timeframe?

Answer 1

Almost all of the well-known mitigation tools yield fast benefits.

PV's payback is around a year. Onshore wind around 3 months, offshore wind around 9 months. The payback time on each of these three depends on the weather regime where it's located. Biomass when done well less has a payback of less than a year. Most energy efficiency measures take less than a decade.

Big hydro takes longer, but is worth doing anyway, as part of the larger long-term decarbonisation strategy.

So this really isn't a case of looking for reasons to exclude mitigation tools on the basis of urgency alone: we must cut emissions by 45% from 2010 levels by 2030, and we must also cut them by 100% by about 2050.