The accelerated recession of mountain glaciers, the retreat of Arctic sea ice and the melting of Greenland’s ice are indisputable markers of global warming. Satellite measurements confirm the rise in the Earth’s average temperature. The recent global warming of the planet is a well-established concept. No one disputes it.

Closely associated with the rise in temperature, and the increase in the concentration of carbon dioxide and all the other greenhouse gases is the signature of a significant change in the chemical composition of the Earth’s atmosphere.

The close evolution between the carbon dioxide levels in the records and the average temperature variations of the Earth over geological time (we are talking here in terms of thousands, or even tens and hundreds of thousands of years) is a strongly established fundamental concept. Ice core drilled from the Vostok site (Antarctica) that serves as a physical record of the last 400,000 years (Figure 1) provides convincing evidence of this close evolution. The correlation of CO₂ and temperature variations remains detectable for the recent period (~past 150 years) as shown by National Oceanic and Atmospheric Administration (NOAA) records documented between 1980 and 2008 at the Mauna Loa observatory (see the NASA website). The concentration of CO₂ in the Earth’s atmosphere varies with temperature with a close trend in the evolution of CO₂ levels and temperature over time.

Breon [3] as contributor to the chapter “Natural and anthropogenic radiative forcings” in the 5^th Intergovernmental Panel on Climate Change (IPCC) report as well as to the summary for policymakers wrote: “The driver of climate change over the last million years is not the same as that over the last century”, and added: “Climatologists are not predicting rising temperatures based on an observed correlation with CO₂ in the past, but on the basis of an understanding of the physical mechanisms that link the two”.

These physical mechanisms, which we cannot conceive to be different from those of the past, would therefore substantiate the founding proposal for a “New Climatology” (one different from that of the past). This New Climatology—i.e. mainstream climatology, (MSC hereafter)—proposes that CO₂ controls the temperature in the first instance. The increase in the CO₂ content in the atmosphere—i.e. CO₂ originating from anthropic activities—must therefore necessarily precede the increase in the temperature. This basic concept has not been demonstrated yet.

Bréon [3] clarifies the axiomatic nature regarding the notion of the antecedence of CO₂: “The rise in temperatures is therefore proven and it is almost certain that it is linked to the increase in the concentration of greenhouse gas”. The wording “almost certain” must be kept in mind. The MSC proposes, without demonstration, that a major disruption in the Earth warming process is currently occurring. This scientific community contemplates that an absence of warming would be more than surprising given the increase in concentrations of greenhouse gases in the atmosphere. However, this is a matter of pure intuitiveness.

Actualism is the assumption that the natural laws and processes that operate in our present-day scientific observations have always operated on Earth in the past. Under the principlesof actualism, evidence in geology can and should be explained in terms of physical processes that are working at present day. Conversely, mechanisms or processes that are at work today are considered powerful models for explaining the cause and effect relationships at play in the development and interpretation of geological situations of the Earth’s past. Actualism is associated with the Scottish geologist James Hutton (1726-1797) often referred to as the “Father of Modern Geology”. He, together with Jean-André Deluc (1727-1817) of France, played a key role in establishing geology as a modern science. Subsequently, these concepts were widely popularized by Charles Lyell (1797-1875).

In geology, Catastrophism is the theory that the Earth has largely been shaped by sudden, short-lived, violent natural disaster events, possibly worldwide in scope. The concept of mass extinction is often considered as an example of Catastrophism. Additionally, meteorite impacts, ice ages, and ocean acidification are all catastrophic phenomena that are categorized as representative events in Catastrophism.

To contemplate major meteorite impacts as originating from exceptional catastrophic events occurring fortuistously outside the normal course of the Earth’s natural history. In that sense meteorite impacts should be considered catastrophic events typical of Catastrophism. In contrast, “ice ages” are geologic events that have repeatedly affected the planet Earth for the past several Myr. Ice ages result from recurring astronomical situations (see below) that can be reconstructed, if they occurred in the past, or that can be predicted in the context of the future of the Earth [1] [4] . Although considered as catastrophic events, ice ages are events representative of Actualism, and they are intimately associated with predictable Earth behavior.

The massive release of CO2 into the atmosphere as the essential cause of the current global warming puts MSC within the framework of an implicit paradigm shift. Indeed, the temperature is no longer considered the parameter that controls the levels of greenhouse gases in the atmosphere as was the case during Earth’s geological past. This would indicate a causal reversal in the recent period. Proponents of the anthropogenic origin of the current warming are implicitly in the philosophical framework of a rupture. The greenhouse gases released in the atmosphere is settling down as the fundamental mechanism for the control of the Earth’s climate. This causal reversal is an exceptional event, never experienced by the Earth. The paradigm framework of the Earth would be changing at this time from Actualism to Catastrophism. The MSC community must carefully documented the antecedence of CO₂ over temperature, this is not an option.

The concept of “climatic aberrations” was first articulated by [1] . These aberrations were short-lived catastrophic events occurring during the Cenozoic (65 Ma to present). They included 1) the thermal maximum at the end of the Paleocene time (LPTM, 55 Myr ago) with an increase in surface water temperature of 8˚C in less than 10,000 yrs and concentrations of 1000 to 2000 ppm CO₂ equivalent in the atmosphere (2 to 5 times more than current levels); 2) the appearance of the Antarctic ice sheet at the Eocene-Oligocene boundary 34 Myr ago, in less than 400,000 yrs; and 3) the glacial maximum at the Oligocene-Miocene boundary (23 Myr ago), whose duration has been approximately 200,000 yrs. The concept of “climatic aberrations” for these one-off events with a very strong geo-climatic signature is paradoxical in that they seem to strengthen Catastrophism as a paradigm. This is not the reality, however since it is the case on the one hand that the history of the planet is punctuated by cataclysmic events, which are the intrinsic, natural expression of the climatic process, and on the other hand, that these events evolved through the antecedence of temperature over CO₂. The paradigm framework for these events is thus the Actualist framework.

A massive release (2600 Gigatons of methane) of seabed methane hydrates (clathrates) occurred during the LPTM event [5] . Because clathrate development requires specific pressure-temperature (PT) conditions at the seabed, such massive destabilization allows it to be inferred that a threshold has been crossed. The sea level that controls pressure at the seabed has a lower potential (i.e. low potential of sea level variation) for variation in destabilization than temperature. Indeed, the LPTM event is characterized by a 5˚C to 6˚C rise in deep sea temperature [1] . Whatever the origin of the seabed warming, it precedes and induces the massive release of CH₄ into the atmosphere.

The other two climatic aberrations of the Cenozoic age were extreme events in Antarctica related to temperature and ice volume [6] [7] . Even if the forcing (disruption of the climate balance) of greenhouse gases is considered a possible amplifier, it is not considered the primary cause of these climatic aberrations. Tectonic evolutions in association with orbital forcing (Figure 2) were the mechanisms triggering these climatic aberrations. These mechanisms act on the

climate system through a physical temperature threshold originating from a reorganization of the ocean/atmosphere circulation, which induces the rapid growth of ice sheets. Here, as during LPTM, the temperature precedes the variation in the concentration of greenhouse gases and then acts as a second-order biochemical feedback in line with the concept of climate sensitivity. The paradigm framework for extreme events in Antarctica is that of Actualism.

The climate system of the Earth’s past shows the existence of temporally punctual and catastrophic natural events. A temperature threshold triggers these global climate events. These recurrent climatic aberrations have different origins and are an intrinsic part of natural climate variability. The increase in current temperature could originate from natural, internal, or external events or mechanisms (such as during the Cenozoic) in which a temperature threshold accelerates the response of the climate system.

The massive release of greenhouse gases associated with human activity could therefore have a hazardous aspect since it would be masking a natural climatic event of an aberrant type. By their very existence, aberrant climatic events support the need to promote more open research than that which is heavily padlocked by the only anthropogenic cause currently envisioned. It would be suitable for the MSC scientific community to abandon the strictly anthropogenic framework. Furthermore the conceptual implications from the “all anthropogenic” explanation seem neither truly evaluated nor fully justified (see above).

Approximately half of human CO₂ emissions remain in the atmosphere, while the ocean and continents (soils, etc.) absorb the rest. This assessment should not mask the core of the problem. It is indeed difficult to truly measure the respective share of natural and anthropogenic emissions at the origin of global warming. In addition, uncertainties remain on the climate response with regard to the lack of information and measurement on this subject.

The available data acquired by the OCO-2 satellite operated by NASA give an idea of the problems in identifying the origin of CO₂ emissions along with the location of absorption areas (CO₂ sinks). The OCO-2 satellite records (Figure 3) show a high CO₂ concentration belt (5˚S - 20˚S belt) connecting the Amazon and Congolese forests to Indonesia. At the same time, developed industrial areas with high population density in the Western world (North America, Western Europe) have relatively modest values with lower CO₂ concentrations. Only China exhibits a strong emission pole. Additionally, the North Pacific, the central Atlantic, and the high latitudes of the Antarctic oceanic belt act as CO₂ sink zones. The OCO-2 satellite map documents one of the main problems for the “all anthropogenic” concept. In the current state of knowledge, the CO₂ concentration in the atmosphere exhibits no distinctive features by which to identify its source. Elevated CO₂ over a region may have a natural cause or a human cause. In the current state, approximately half of the CO₂ emissions originating from human

activities remain in the atmosphere, while oceans and land sinks are removing the rest. In other words, no evidence exists discriminating anthropic CO₂ from natural emissions.

Sea level variations globally are a record of the physical and chemical factors controlling climate evolution over time. These factors include temperature and CO₂ regardless of the antecedence of one over the other. In other words, the sea level provides no evidence for identifying its origin, be it natural or induced from increases CO₂ concentration in the atmosphere that is connected to human activities.

Melting of ice sheets such as those from Antarctica, Greenland, and Patagonia is inducing sea level rise [8] [9] [10] . A sudden and significant rise of the global ocean would be a catastrophe since 20% of the world’s population lives along the coastal areas. This potential hazard erected, as an imminent threat by the MSC becomes a prediction and thus is becoming a political weapon.

The global mean sea level (GMSL) rise results from two basic factors. These include a thermal expansion of seawater as it warms and water inflow from melting glaciers and ice sheets. Because the IPCC scientific community currently considers anthropogenic factors to control climate evolution the future rise in GMSL is believed to be dependent on which emission scenario is followed. In this line of thinking, sea level rise at the end of the century is projected to be faster under all scenarios, including those compatible with achieving the long-term temperature goal set out in the Paris Agreement. “GMSL will rise between 0.43 m (0.29 - 0.59 m, likely range; RCP2.6) and 0.84 m (0.61 - 1.10 m, likely range; RCP8.5) by 2100 (medium confidence) relative to 1986-2005”.

Predicting our environmental future involves properly reading records from the geologic past of our planet. Sea level has risen by 120 to 130 m (Figure 4) since the Last Glacial Maximum ~20 ka. There is a great deal of reliable and concordant data that strongly documents this assertion. Assuming a linear evolution over time, this increase would be 0.65 m per century on average. We know that this is not the case because the sea level rise was rapid between 20 and 6 ka, and then slower thereafter. Sea level rise was ~6 m for the past 6 kyr, which would correspond to a rise of 0.10 m per century on average for the last six millennia.

The IPCC data reported a rise of 0.16 m ± 0.04 m for the period 1902-2015, which corresponds to a value of 0.14 m ± 0.03 m for a century. The excess rise in sea level proposed by the IPCC compared to that measured by geological records is between 1 cm and 7 cm for the period 1915-2015. Another IPCC estimate for the period 1901-2011 is somewhat higher at 0.16 m per century. Assuming that the reported measurements are accurate, we can conclude [12] that the sea level has risen by a maximum of 10 to 16 cm during the last century (between 1915 and 2015). Therefore, the IPCC accepted sea level rise for the period 1915-2015 is close to that reconstructed from geological data for the past 6 kyr. No evidence from geological archives exists documenting a catastrophic sea level rise by the end of the 21^st century.

Indeed the average sea level rise measured by the TOPEX-POSEIDON and

JASON satellites documents a rise of 0.04 m for the period 1995-2010, which would allow a projection of 0.26 m per century. Other measurements converge toward values that do not exceed 0.30 m per century [13] [14] . These values are far from those in the data published by Hansen [15] . He calculated a 1 cm contribution from ice sheets for the decade 2005-2015 and that it doubles each decade until the West Antarctic ice sheet is largely depleted. That time constant yields a sea level rise on the order of 5 m this century. Even though it has been largely diffused, the 5 m catastrophic scenario has been subsequently abandoned. In the recent years the IPCC has reported a sea level rise ranging from 0.50 to 2.40 m, depending on different greenhouse gas concentrations in the atmosphere, in the coming years to 2100.

Sea level rise as restored from the projection of geological data—i.e., records for the ~past 6 kyr—and that reconstructed from meteorological data—i.e., ~from the last century—are suggesting no flagrant sea level rise break development in the near future. Sea level rises based on estimates from models (IPCC, 2019) will be higher by an order of magnitude by the end of the century [16] . Sea level rise as a comprehensive record shows a conceptual break between the projections (Actualist framework) from geological dataset and the prediction (Catastrophism framework) from IPCC conceptual models exists.

Hansen et al. [17] published a synthetic article outside the UN collegial assessments. It provides the general scientific frame for the IPCC climate philosophy. The last sentence of the abstract from this publication—“Burning all fossil fuels, we conclude, would make most of the planet uninhabitable by humans, thus calling into question strategies that emphasize adaptation to climate change”—supports the alarmist character widely propagated by the IPCC community. The Hansen et al. [17] publication also offers the opportunity to address discussion points of general interest such as the role of the Earth’s orbital parameters, the contributions of ice drilling or the central concept of climate sensitivity. The following considers four discussion specific points including orbital parameters, temperature and CO₂ decorrelation, the climate sensitivity concept, and models.

The evolution of orbital parameters controls the insolation—i.e., the temperature

—of the Earth through time. This in turn induces the periodic variations in the Earth’s climate, at least for the past 800 kyr. Ice coring (in Antarctica, and Greenland) documents a close covariation of temperature and CO₂ content in the atmosphere during time periods of Earth warming (Figure 1). In contrast, a strong decorrelation of these two parameters characterizes the time periods of a cooling Earth extending from climate optimums to terminations. No evidence exists documenting CO₂ antecedence over temperature during warm/cool Quaternary cycles.

During the Cenozoic, major events, such as the Late Paleocene Thermal Maximum or the glacial event that was initiated by the appearance of the Antarctica ice sheet at the Eocene-Oligocene boundary were primarily thermally controlled. The associated CO₂ content variation in the atmosphere occurred in the wake of thermal events through second-order forcing, positive or negative.

Conversely, the MSC considers the massive release of greenhouse gases in the atmosphere to be the main cause of warming in recent decades. This entails an implicit paradigm shift since the cause during the past history of the Earth then is presented as the consequence for the present time. This basic point is not demonstrated or even discussed. Qualified as “virtually certain”, this becomes an axiom for the MSC models. By using ad hoc sensitivity parameters in their “efficient climate model” [17] discussion regarding CO₂ antecedence over temperature and associated paradigm shift can be avoided.

Basically, the MSC scientific community proposes models built on the idea of CO₂ antecedence over temperature. Because no evidence exists for this antecedence, something must be done to palliate this gap. That will entail testing the efficiency of the models for reproducing parameters characterizing the climate evolution for specific time periods of the Earth’s past. Because these time periods are entirely controlled by the antecedence of temperature, it makes no sense to test a model based on the reverse—i.e., CO₂ antecedence over temperature—. The back and forth from one paradigm to another (from Catastrophism to Actualism) explains, at least in part, the failure of the models as noted by Koonen [13] —i.e., “Many muddled models” p. 77-96.

Considering that the antecedence of CO₂ over temperature has not been demonstrated, other avenues of research should be explored to characterize the possibility of an origin, not yet identified, of the current increase in temperature of our planet. If accepting that the main target is fighting against global warming, it is imperative to explore its potential origins in an exhaustive way.

The Earth’s climate is currently in a climatic optimum phase (warm) comparable to the Eemian (128 ka). At that time, our planet was at the dawn of a shift toward a new glaciation [18] . The current warming could be just a short-lived incident masked by anthropogenic emissions Between 128 and 114 ka a decorrelation existed between the CO₂ and temperature. For 14 kyr, CO₂ remained stable, while the temperature dropped even though these two parameters are usually linked. Understanding the climatic process at the origin of such de-correlation can represent a way out for the climate anthropic dogma.

The author declares no conflicts of interest regarding the publication of this paper.

Bourgois, J. (2024) The Sword of Damocles behind the Curtain of the Earth’s Global Warming: A Review. International Journal of Geosciences, 15, 119-136. https://doi.org/10.4236/ijg.2024.152009