The Rule of Climate Change.

It seems, to this non-expert, that a simple rule has been forgotten, even by the supposed 'experts' on the climate, that, if we reproduce the atmospheric chemistry of the past, other things being equal, we will reproduce the climatic conditions of the past.

This rule deserves, and needs, to be reiterated, and emphasised, in all the introductory textbooks on climatology.

So it is that the atmospheric chemistry of the Mid-Piacenzian Warm Period (MPWP) of the Pliocene Epoch, 3.35-3.15 million years ago (Mya) is being reproduced in this decade, with the orbital configuration of the Earth no different to then (or, at any rate, insufficiently different to have any appreciable impact) and the Sun's luminosity actually brighter by between 0.0286-0.0345% (the gain in luminosity being 0.01% every 1.1 My). See: de la Vega, et al (2020); Schröder and Smith (2008), p.157 (p.3, pdf.).

If the maximum atmospheric CO2 level in the MPWP was 428 ppm, and the mean annual global near-surface atmospheric temperature was 3 °C above the Holocene pre-industrial (1750) norm, what gives us any rational expectation that that situation won't be reproduced, or that temperature even exceeded, given the Sun's greater luminosity?

The current equilibrium climate sensitivity (ECS) appears to be of the order of 3.58628 °C, translating a CO2 level of 422.37 ppm into global warming of 1.5 °C, but the El Niño being experienced at the moment is a complicating factor. Without that, the ECS might be closer to 3 °C, giving ~1.255 °C of warming, a difference of 0.245 °C.

What is clear is that, if 428 ppm translates into 3 °C of global warming, the ECS that matches that must be 6.952458 °C, which is 131.7486% larger than the 3 °C of the AR6 Technical Summary, p.46 (p.14, pdf.). See Meehl, Senior et al (2020), but even this is of limited relevance.

Thus it would appear that, once CO2 rises above a certain threshold, ECS increases dramatically, and the mean annual global near-surface temperature increases likewise. The evidence of the MPWP is clear, but appears to be being ignored, and largely for political reasons, because it is simply too uncomfortable for the politicians and the fossil fuel companies.

The fact is, our global capitalist economy is totally dependent on fossil fuels, and thus cannot avoid generating CO2 emissions. The supposition that renewables, or renewables and nuclear, can substitute entirely for fossil fuels, perhaps aided by such props as CCS technology and 'biofuels', is pure fantasy, because that economy has to grow each year, and is also dependent on a growing global population, to supply more workers and, above all, consumers, all of whom need feeding, watering, clothing, housing, educating, etc.

This inevitably entails ever-increasing demand for resources from a finite planet, and - of course - more and more energy, which renewable and nuclear energy cannot meet, leaving a gap for fossil fuels to fill. OPEC expects global energy demand to increase by 23% to 2045, and global demand for oil to increase to 110 million barrels a day, 40.15 billion barrels a year that same year, & investing $12.1 trillion in the oil sector to that year, see: Vanguard News.

This is $550 billion a year from this year, 2023, until 2045, inclusive - $550 billion a year invested in more annual and cumulative CO2 emissions! And this call comes from the mouth of the Director-General of OPEC himself, who boasts of the investment the OPEC countries are making in renewables, and prides himself on the fact that COP28 is taking place in the UAE!

That 40.15 billion barrels of oil in 2045 will equal about 5.4775 billion tonnes of oil, equivalent, if they were burned as oil, to 1.2848 trillion tonnes of CO2 (1,284.8 Gt), or ~164.63 ppm. Never mind the gas and coal burning, or any other GHGs!

If what OPEC are forecasting has any bearing on what turns out to be the case, then all talk of 'Net Zero by 2050' is, quite simply, utterly risible.

We cannot go on as we are doing: if we do, we are doomed, and in the not-very-distant future, either. We have to change course. In the immortal words of the late Baroness Thatcher: There Is No Alternative!