Martin J. Head’s research while affiliated with Brock University and other places

Plain Language Summary The extraordinary fossil fuel‐driven outburst of consumption and production since the mid‐twentieth century has fundamentally altered the way the Earth System works. Although humans have impacted their environment for millennia, justification for a new interval of geologic time lies in the radical shift in the geologic record that marks this “Great Acceleration” of the human enterprise. The rejection of a proposal to define the beginning of the Anthropocene epoch with a “golden spike” in varved sediments from Crawford Lake, Canada, means that we officially we still live in the Holocene, when in practical terms we do not. Formal recognition of the Anthropocene will acknowledge the facts supporting global warming and many other planetary changes that are irreversible on geologic time scales, aligning the Earth Sciences with geologic, planetary and societal reality.

From the Abstract: The biogeophysical and socio-political knowledge of the Anthropocene, while transforming our understanding of the Earth System, is also renewing our understanding of human existence and raising questions about education at a time when profound existential challenges are looming. These issues are now inextricably linked. Human existence, and the Earth System, are caught up within three fundamental trajectories. In the planetary dimension, this is leading towards a rapid shift in climate, already outside of conditions previously experienced by organized human societies. In the terrestrial dimension, many ecosystems have become highly degraded [18, 19], as is also the case in the seas, as with, for example, coral-based reefs [20]. And, in the global dimension of our societies, the dominant process is an acceleration of technological, social, and political change. Processes of shift, collapse, acceleration reinforce each other, impacting (unequally) on human communities. (for full poster abstract see full text)

From the Abstract: The technosphere sensu Peter Haff [12] has auton- omous qualities, being not so much human-directed as incorporating dependent, strongly divided human soci- eties, while parasitizing its parent biosphere for energy and materials. By far the most recent and rapidly evolving of Earth’s ‘spheres’, it is also the most unsta- ble, recycling far fewer of its resources than the bio- sphere, its accumulating waste products in all other “spheres” simultaneously threatening biosphere integ- rity and its own continued existence. The techno- sphere’s potential future pathways are highly disparate: a) will it continue to rapidly degrade the biosphere as a parasite, likely causing a mass extinction and thus a reset in the trajectory of biological evolution?; or b) can it evolve (or be steered) rapidly into mutualistic relations, in which case its functional interaction with the biosphere may well represent a new Earth state? More immediate issues include managing its potential for environmental management, e.g. via satellite ob- servations – while simultaneously avoiding making near-space unusable by accumulation of orbiting tech- no debris. For the time being it is a key analogue, the only one known, in considering the possibilities and fates of intelligent, manipulative life elsewhere in the cosmos. (see full text for entire conference abstract)

From the Abstract: The Anthropocene is a particularly powerful con- ceptual tool, and encapsulates the complex intercon- nectivity of all the ‘-spheres’ on this planet. It quickly became a key framing concept for Earth System re- searchers. From this, and from its subsequent geologi- cal analysis, it grew to spark off considerable cross- disciplinary dialogue among the social as well as phys- ical sciences, and the humanities and arts, involving fundamental humanistic questions such as the relations between nature and culture [23, 24]. More widely, it enables a vision of the world (scientific, political, eco- nomic, cultural, etc.) that is grounded in reality, and that helps frame societal questions of sustainability. An Anthropocene literacy may help sketch out different, evidence-based, pathways into the future of this planet [25], even as the effects of this new epoch extend out to other planetary bodies [26, 27]. (for the entire conference abstract see full text)

We synthesize research from complementary scientific fields to address the likely future extent and duration of the proposed Anthropocene epoch. Intensification of human-forced climate change began from about 1970 onwards with steepening increases in greenhouse gases, ocean acidification, global temperature and sea level, along with ice loss. The resulting distinction between relatively stable Holocene climatic conditions and those of the proposed Anthropocene epoch is substantial, with many aspects irreversible. The still-rising trajectory of greenhouse gas emissions is leading to yet greater and more permanent divergence of the Anthropocene from the Holocene Earth System. We focus here on the effects of the ensuing climate transformation and its impact on the likely duration of this novel state of the Earth System. Given the magnitude and rapid rise of atmospheric carbon dioxide (CO2), its long lifetime in the atmosphere, and the present disequilibrium in Earth’s energy budget (expressed as the Earth’s Energy Imbalance, or EEI), both temperatures and sea level must continue to rise – even with carbon emissions lowered to net zero (where anthropogenic CO2 emissions = anthropogenic CO2 removals) – until the energy budget balance is eventually restored. Even if net zero were achieved immediately, elevated global temperatures would persist for at least several tens of millennia, with expected levels of warmth by the end of this century not seen since the early Late Pliocene. Interglacial conditions are likely to persist for at least 50,000 years under already-accumulated CO2 emissions and Earth’s low eccentricity orbit. Continued increases in greenhouse gas emissions are likely to extend that persistence to around 500,000 years, suppressing the pronounced expression of Milankovitch cyclicity typical of the later Pleistocene Epoch. This major perturbation alone is sufficient to justify the Anthropocene as terminating the Holocene Epoch. The wider and mostly irreversible effects of climate change, not least in amplifying reconfiguration of the biosphere, emphasize the scale of this departure from Holocene conditions, justifying the establishment of a new epoch. Given such perspectives, the Anthropocene epoch represents what will become a lasting and substantial change in the Earth System. It is the Holocene Epoch at only 11,700 years duration that will appear as the ‘blip’ in the Geological Time Scale, a brief interval when complex, settled human societies co-existed with, but did not overwhelm, a stable Earth System.

Increasing human interactions with the biosphere over tens of millennia have left a fossil record that shows the growing geographical spread and technological sophistication of humans evident in patterns of extinction and domestication of the landscape and its plants and animals. Here, we focus on the "Great Acceleration" of the mid-20th century (e.g. Steffen et al. 2015) which provides the causal mechanism of the proposed Anthropocene epoch (Waters et al., 2023) in which rapid increases in human and domesticated animal populations, energy consumption and technological innovation coincide with globalization of industry and commerce. Key parameters and their diagnostic palaeontological signals of the Anthropocene include: 1) the rapid breakdown of discrete biogeographical ranges for marine and terrestrial species with successions in North America, South America, Africa, Oceania, Europe and Asia correlatable using palaeontological signatures of highly invasive species and changes to ecologies that demonstrate the growing interconnectivity of human systems through expansion of global shipping, road networks, physical connection of water masses and recent development of aquaculture; 2) rapid changes to ecologies resulting from climate change, e.g. loss of coral reefs and poleward shifts of species through thermal stress, and ecological degradation, e.g. nutrient enrichment in lakes and coastal zones causing eutrophication and hypoxia, and extensive damming of rivers inhibiting movement of species and causing local extirpation; 3) an 'acme biozone' of human and domesticated animal skeletons co-occurring with a domesticated plant pollen record and coincident with greatly reduced populations, ecological ranges and extinctions of ‘wild’ species; 4) the rising volume and unique depositional settings of landfills containing large quantities of organic wastes recording the spread of exotic foodstuffs far beyond their geographical range of environmental tolerance, notably of seeds of internationally traded fruits, e.g. avocados, coconuts, mangos and peaches; and 5) the accumulation of reconfigured forest materials including paper, paperboard and engineered wood products such as medium density fibreboard (MDF). The presentation addresses how a range of depositional settings may preserve a long-lived, unique palaeontological record for post- mid-20th century deposits that is distinct from all past records of deep-time biotic change, including those of the Holocene, and is consistent with the proposal of the Anthropocene as an epoch of geological time.

Applying the basic principles of carbon chemistry and physics, along with a comprehensive understanding of past climate change, Steffen and colleagues confirmed in the Proceedings of the National Academy of Sciences 115, in 2018, that fossil fuel usage and resulting carbon emissions will cause substantial global warming into future millennia. The climate shift caused by increasing greenhouse gases is provoking a major perturbation to the Earth System likely to last for hundreds of thousands of years according to Talento & Ganopolski in Earth System Dynamics 12, in 2021, because of (i) the long residence time of CO2 in the atmosphere; (ii) the reduced ability of the global ocean to serve as a carbon sink as warming continues; (iii) the release to the atmosphere of CO2 currently stored in the ocean to maintain chemical equilibrium between the ocean and atmosphere as emissions of CO2 begin to decline; (iv) the decrease in albedo through continuing ice melt; and (v) a transgression forced by sea level rises of 10-15m or more supplying organic rich sediments to coastal seas and thus increasing the ocean’s carbon content. These drastic changes and associated largely irreversible changes to the biosphere justify the creation of a new epoch – the Anthropocene. Intensification of the greenhouse effect results from the growth in emissions of the CO2 equivalent (CO2-eq), calculated as the sum of the effects of CO2+CH4+N2O+CFCs and other trace gases. According to NOAA’s Annual Greenhouse Gas Index, in spring 2022 the CO2-eq had reached 523 ppm. Such high concentrations of greenhouse gases in the atmosphere are above those identified in the early Late Pliocene, around 3.5 Ma ago, and are close to those identified for the mid-Miocene (16.9–14.7 Ma ago), which were known intervals of uncommon warmth during Neogene times. According to the IPCC’s 6th assessment report (of 2023) projections based on intermediate emissions scenarios place us on track by 2100 to experience CO2 concentrations of 600 ppm that would raise mean global temperature by 2.7°C, a level higher than experienced during Quaternary time. That same report considered that global mean sea-level rise approaching 2m by 2100 and over 15 m by 2300 cannot be ruled out due to deep uncertainty in ice sheet processes, with severe impacts on coastal populations. The ensuing prevention of the glacial maxima typical of the past 1 Ma is expected to last at least 500,000 years, assuaging concerns that the Anthropocene it too short in duration to qualify as a new epoch.