2.9 Interglacials of atypical duration

generally accepted, but the recent proposition that CO2 is the “principal control knob governing Earth’s temperature” (Lacis et al. 2010), here referred to as the CO2 hypothesis, lacks in supporting evidence.

Chapter 10 examines one of the most fundamental and least well-known properties of the climate system, the meridional transport of energy along the latitudinal temperature gradient. It involves the stratosphere, troposphere, and ocean in a not well understood coupling, that is variable in time and space. Most of the variability in the energy transported is seasonal, tied to the strengthening of the winter atmospheric circulation when the temperature gradient becomes steeper. Evidence is presented that relates different climate phenomena to changes in this transport, examining the role of the Quasi-Biennial Oscillation, El Niño/Southern Oscillation (ENSO), and the solar cycle in modulating meridional transport. A particularly neglected piece of evidence is crucial to revealing the solar modulation of meridional transport, as changes in atmospheric circulation can be related to the correlation between the solar cycle and changes on Earth's rate of rotation (Lambeck & Cazenave 1973; Le Mouël et al. 2010). The effect of changes in solar activity on ENSO is far from being accepted, despite an abundant bibliography. The possibility that ENSO acts as a tropical pump linked to meridional transport leads to new evidence of the solar modulation of ENSO presented in this book.

Chapter 11 is a continuation of chapter 10, reviewing the evidence that two drivers of climate change, volcanic forcing and multidecadal internal variability, induce changes in meridional transport. It is known that changes in multidecadal oscillations are associated with climate regime shifts (Tsonis et al. 2007). Evidence is presented in support of one such shift taking place in 1997–98, associated with a change in meridional transport, that altered the energy budget of the planet. This evidence leads to the intriguing possibility that meridional transport changes constitute an unrecognized climate change driver. An allencompassing hypothesis is presented to propose that meridional transport is the principal driver of natural climate change. This hypothesis links all other natural causes, volcanic eruptions, multidecadal internal oscillations, ENSO, and solar activity, through their effects on the amount of energy directed to the two gigantic cooling radiators that the planet has at its poles in the current ice age. This hypothesis is named the Winter Gatekeeper because the variable amount of energy lost by the planet at the winter dark pole is proposed as the main climate effect mediator.

With the knowledge gained about natural climate change, modern global warming is examined in chapter 12. The recent warm period presents some highly unusual characteristics, like its non-cyclical cryosphere retreat that appears to have undone most of the Neoglacial advance, and its human-caused very high, and fast rising, CO2 levels, higher than at any time during the Late Pleistocene. But unlike the anthropogenic forcing, the increase in temperature and sea level over the past 120 years shows little acceleration. According to the evidence the anthropogenic contribution is clear, but how much is human-caused and how much is natural is still an open question. The IPCC and most climate scientists are confident of the answers provided by climate models. Whether they deserve such confidence remains to be seen.

The IPCC has decisively contributed to the climate “emergency discourse” through the development of a series of gloomy future scenarios, not only in temperature but also in other climate phenomena, like sea-level or Arctic sea-ice. Leaving aside the debate about how unusual the IPCC’s business-as-usual scenarios are, chapter 13 attempts to produce an alternative set of projections. Unlike IPCC projections, they consider fossil fuel supply side constraints and human population dynamics. They also take advantage of the advances made by systematic studies on forecasting (Armstrong et al. 2015). The golden rule of forecasting establishes the need to be conservative and adhering to cumulative knowledge about the subject. The set of conservative climate forecasts for the 21st century presented in chapter 13, is opposite to IPCC's wildly extremist projections. Time will be the final arbiter between this author's modest efforts and IPCC's multi-milliondollar bureaucracy’s scientific projections.

The final chapter deals with the very distant future when the present interglacial should come to an end and the planet returns to the glacial conditions that have dominated the Pleistocene. The IPCC has reached the outlandish conclusion that a new glacial inception is not possible for the next 50 kyr if CO2 levels remain above 300 ppm (Masson–Delmotte et al. 2013). The evidence presented in chapter 14 shows that glacial inceptions have taken place for the past two million years every time obliquity has gone below 23° during an interglacial. Interglacials are simply unsustainable under low obliquity conditions and there is no evidence that this time will be different. The long interglacial hypothesis rests on the wrong astronomical parameter, high equilibrium climate sensitivity to CO2, and uncertain model predictions of very slow long-term CO2 decay rates. The evidence supports a long delay between orbital forcing and its global ice-volume effect. If correct, the orbital threshold for glacial inception is crossed several millennia before glacial inception takes place. The orbital threshold calculated for the interglacials of the past 800,000 years supports that it was crossed for the Holocene 1400–2400 years ago. This interpretation of the evidence suggests that it is just a matter of 1500–4500 years before the next glacial inception takes place, putting an end to the Anthropocene.

The future is unknown, but unless we attempt to answer the outstanding questions about natural climate change reviewed in this book, the climate science of the future will not have a solid foundation. Science is about skepticism and debate. In the words of Richard Feynman:

“Once you start doubting, just like you’re supposed to doubt. You ask me if the science is true and we say 'No, no, we don't know what's true, we're trying to find out, everything is possibly wrong' … When you doubt and ask it gets a little harder to believe. I can live with doubt and uncertainty and not knowing. I think it’s much more interesting to live not knowing, than to have answers which might be wrong.” (Feynman 1981)

If we disallow the skepticism and the debate, we end with no science.