Decades for global temps to start falling

From ZME Science.

Global warming is perhaps the ultimate hurdle humanity will have to overcome in our lifetime. Researchers from Norway are helping us get a better idea of what that process would entail.

According to their work, it could take decades after we reduce greenhouse emissions for the planet to start cooling down. While the idea that it takes time to alter climate patterns — known as ‘climate inertia’ — isn’t new, the study does offer a more in-depth estimation of how such a process would unfold.

The study was published by three researchers at the CICERO Center for International Climate Research in Oslo.

They worked with several climate models to determine how global climate would respond to different levels of reductions in greenhouse emissions, or to changes in the overall make-up of those emissions.

Slashes in carbon dioxide emissions were the only changes that had a noticeable effect on global warming, but even then, it would take a long time to see progress.

However, when emissions of other gases being emitted were reduced as well, this cooling trend would accelerate. If these other pollutants are not reduced, the planet will cool down very slowly.

According to the team’s best-case scenario (near-zero-emissions starting this year), we’ll see the planet starting to cool down somewhere in 2033. Under the RCP 2.6 scenario (an emission reduction scenario considered to be achievable by many researchers and politicians), the team saw no positive changes until 2047. Finally, if emissions are reduced by around 5% each year, we’ll start seeing an improvement by 2044.

RCP stands for Representative Concentration Pathway:

RCP 2.6 is a "very stringent" pathway. According to the IPCC, RCP 2.6 requires that carbon dioxide (CO2) emissions start declining by 2020 and go to zero by 2100. It also requires that methane emissions (CH4) go to approximately half the CH4 levels of 2020, and that sulphur dioxide (SO2) emissions decline to approximately 10% of those of 1980-1990. Like all the other RCPs, RCP 2.6 requires negative CO2 emissions (such as CO2 absorption by trees). For RCP 2.6, those negative emissions would be 2 Gigatons of CO2 per year (GtCO2/yr). RCP 2.6 is likely to keep global temperature rise below 2 degrees C by 2100.

A  3% per annum compound decline in emissions would reduce them to 9% of 2020 levels by 2100, which doesn't seem particularly "stringent" to me, as we will transition electricity generation and surface transport to zero carbon by 2035, and those total roughly half of all CO₂ emissions globally.   

In addition, it seems to me very likely that global CO₂ emissions peaked in 2019.  Thanks to the covid crash, global CO₂ emissions will prob'ly fall 4.5% this year.  Yes, they will rise again as economies recover, but the recovery will be sluggish.  Let's say we get back to 2019 world GDP by mid-2022.  That would give us another 2 years for renewables costs to fall: solar by 25-30%; wind by 15%; batteries by 35%, and EVs by 10-15%.  Even in China, unsubsidised solar is already below grid parity, i.e., is now cheaper than the cost of wholesale electricity from the grid.  Another 25-30% decline in the costs of solar will accelerate the switch away from coal, and (be warned) soon from gas too.  So there is an excellent chance that emissions in 2022 will be a little below emissions in 2019, and from then on will  start to fall fast.

So, according to the analysis by the CICERO Center for International Climate Research, global temperatures will peak by 2050.  Good news.

 Wikipedia
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