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Comment by romaaeterna | Hacker News Reader

There was an article in Nature the other year about AMOC periodicity across a long term timescale. Apparently you get high temperatures, then instability, then a gulf stream reversal every few thousand years, followed by glaciers coming south.

Long term temperature increase due to complex systems like AMOC could explain why we see measurable linear temperature increases starting in the 1880s, instead of the 1940s as CO2 forcing might predict, have historical evidence of extremely cold weather in classical Europe (frozen Rhine, etc.), and have evidence of warmer temperatures than today with the Holocene maximum about 8,000 years ago.

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> measurable linear temperature increases starting in the 1880s instead of the 1940s

Could you cite your sources on this one? Every graph I can find shows the linear increases starting in about 1920 (plus or minus a bit, depending on how you squint your eyes), and correlating very neatly with atmospheric CO2 concentrations.

[1] https://www.metlink.org/wp-content/uploads/2020/11/200_years...

[2] https://qph.cf2.quoracdn.net/main-qimg-bbbf79f1dadb29616e78b...

[3] https://www.researchgate.net/profile/Robert-Stavins/publicat...

[4] https://berkeleyearth.org/wp-content/uploads/2024/01/AnnualP...

The lake next door to my house has had ice-in ice-out dates measured by the local university using the same procedure for the past 170 years. Lake ice is an extremely good way to determine average temperature for a season, of course, as it's just a big mass that gets cold and warms up again.

When you plot my lake, it's a solidly linear trend of fewer days of ice coverage ever since they began measuring it.

The neat atmospheric CO2 correlation is presumably the same thing that has caused that same correlation to exist in pre-historic times: CO2 has been a correlated trailing indicator of global temperature through the entirety of Earth's history.

If there has been a long-term global trend for Earth temperatures, like my little (not so little actually) lake seems to indicate, some of the assumptions that establish CO2 radiative forcing as a cause rather than an effect go out the window entirely.

But don't take my word for it. Read this Nature paper, and add in the postulate that global temperature since the 1860s is some linear trend similar to my lake's temperature, and watch what comes out:

https://www.nature.com/articles/srep21691

I don't mean to be rude, but your sources are: The lake next to your house, and a paper that opens with

> it is confirmed that the former, especially CO2, are the main causal drivers of the recent warming.

Your claim that warming is caused by natural cycles doesn't seem to be very well supported here.

I can be of no help to anyone who only reads the first sentence of a paper and stops, especially when I asked him to read the whole thing. Also anyone with minimal necessary background on temperature proxies for 1850-1890, or a good background on the temperature proxies or models that generate the links you have provided, will immediately see the comedy in "my little lake." But if you want to polemics rather than breadcrumbs from me, you are interacting with the wrong person.

To put it very simply: our evidence for a high feedback factor for added CO2 in the atmosphere and evidence for the forcing effect is entirely dependent on the assumption that temperature was not increasing much before 1940s.

> Long term temperature increase due to complex systems like AMOC could explain why we see measurable linear temperature increases starting in the 1880s, instead of the 1940s as CO2 forcing might predict

What predictions would this hypothesis suggest (that aren't also shared with CO2 forcing)?

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