By Andy May
Most agree that the Milankovitch cycles of eccentricity, obliquity, and precession drive long-term global and hemispheric climate changes, see figure 4 in this post for a brief description of them. The modern climate debate is about short-term climate change. The “consensus” says that human emissions have caused “the most rapid change” or “temperatures are the warmest in X years” (Lecavalier et al., 2017) and (IPCC, 2021, p. 8) with X varying from one thousand years to over 100,000 years. Obviously, we only have global instrumental data for the past 170 years or so, so any global or hemispheric data before then is either local or proxy temperature data.
The mainstream view is to ignore inconvenient data that shows CO2 and methane air concentrations do not correlate with temperature during the Holocene Epoch, or the past 12,000 years as shown in figure 4 here. Correlation is not causation, but the lack of correlation normally precludes causation. If changes in heat storage in the climate system are ignored, as is often done, then only outside forcing can cause climate change. Since recent climate changes (since 1950) have been too rapid to be caused by the Milankovitch orbital cycles, the only outside forces left are the Sun and greenhouse gases (GHGs). Since the oceans and atmosphere change the amount of heat they store, as opposed to emit to space, climate changes as climatic heat storage changes (Irvine, 2014). We can observe this in the 60-70-year climate or ocean oscillations, like the Atlantic Multidecadal Oscillation (AMO, see here and here).
