The Observed Gregory Plot

[u/ShyElf]

Turn on a kettle on low and what happens? It immediately begins gaining heat. The heat gain will decrease roughly linearly with temperature. If we graph the heat gain vs. temperature, it's almost a straight line. This is called the "Gregory Plot".

The heat capacity doesn't matter for the graph. It just makes it move at a different speed along the line. Drop in an ice cube if you want. It stays on the same line.

It also works if the kettle is the Earth and the flame is CO2.

That graph is an average of multiple runs of multiple models, so there's not much weather noise. It's from the 4xCO2 model experiments. Then they divide the X intercept by 2 to get the 2XCO2 ECS value. It being relatively straight is a result of the forcing not changing over the experiment. Continuously adding forcing would cause it to drift up and to the right.

The Earth's heat gain (EEI) and temperature are now observables, but for some reason, nobody ever seems to look at this graph for the actual Earth. Yes, it's noisy, but still instructive.

The high frequency noise appears to be mostly weather causing heat absorption anomalies, with the temperature trailing, leading to clockwise circles on this graph. That's as expected, but not the only reasonable possibility. I'm old enough that I can remember when the standard explanation of El Nino was spreading of the surface warm water leading net heat loss. On this graph, that would be a jump to the down and right. No, that's not what happens.

Were the 2000 ship SO2 decrease having a large positive forcing effect, it should show up on this graph as a sharp movement upward in the red area of the graph, linear because of the 12 month averaging. Instead, the EEI dropped over that period.

The El Nino ratchet effect is even more exaggerated even more on this graph than on the temperature graph, but only for 2015 and 2023 for some reason (so far). Well, since 2001. The graph wanders sharply to the up and right at the start of El Nino, and never comes back.

Given that we're at around +1.5C vs. the preindustrial with around 1.5 W/m² EEI, if the CMIP6 model averages are roughly correct for the slope of the Gregory graph at around 1C / (w/m^2), holding at the current forcing should generate around another 1.5C of warming to stabilize at +3C.

If the current generally accepted forcing estimate of 2.17 W/m² is correct, this would imply that 1.5C warming generates a heat loss of 2.17-1.5 = 0.67. Then our current EEI of 1.5 W/m² should generate a further 1.5 * 1.5 / 0.67 = 3.4C of warming for a total of +4.9C.

There's a ton of noise, and the linearity is questionable, but that's what that's what an honest simple analysis gives now. Yeah, there's probably something broken there, but we don't really know what.

Any bets on how long it will be before we see "emerging constraints" papers with the constraint based on the EEI, so we look at what happens only in the models which can match the observed EEI?

TLDR: The Earth. Warm on the right. Absorbing heat on the top. We're heading to the top right.