The Past as a Mirror: Deep Time Climate Change Exemplarity in the Anthropocene

Abstract

During the past decades, notions of Earth dynamics and climate change have changed drastically, as anthropogenic CO 2-emissions are linked to measurable Earth system changes. At the same time, Earth scientists have discovered deep time climate changes triggered by large scale and natural release of CO 2. As the understanding of past climatic changes improved, they were used to envision what might happen in the near future. This article explores the use of deep time climate examples by analyzing publications on a 56-million-year-old greenhouse gas-driven rapid global warming event, the Paleocene-Eocene Thermal Maximum (PETM). We explore how the PETM is framed and used as an example of "extreme climatic warming" in four cases across different scientific genres. The scientific knowledge about the PETM is considered too uncertain to draw conclusions from, but our analysis shows that, by being presented as an example, the PETM may still contribute to the scientific understanding of ongoing climate change. Although the PETM is regarded as too uncertain to guide present day climate change modeling, it is still considered morally significant, and is allowed to influence public opinion and policy making. We argue that the PETM is used as an example in ways that have formal similarities with the early modern historia magistra vitae topos. The PETM example highlights the ambivalence that characterizes the Anthropocene as a temporal conception. The Anthropocene is "completely different", but at the same time pointing to the similarity between the present and the deep past, thereby allowing for comparison to past geological events. Thus, the Anthropocene is not so "completely different" after all. Just a little bigger, a lot faster, and a lot scarier to humans.

Rapid and sustained environmental responses to global warming: the Paleocene–Eocene Thermal Maximum in the eastern North Sea

“…The 4-5 • C PETM temperature increase (Thomas et al, 2002;Dunkley Jones et al, 2013;Frieling et al, 2017) is comparable to that predicted in response to the current anthropogenic carbon emissions (Riahi et al, 2017). The PETM is therefore an important natural analogue for future greenhouse conditions, as the environmental and ecological response may hold clues for the consequences of present-day global warming (Zachos et al, 2010;Alley, 2016;Penman and Zachos, 2018;Svensen et al, 2019). Model predictions suggest that the current global warming will lead to an enhanced hydrological cycle, akin to that indicated by PETM proxy records (Held and Soden, 2006;Seager et al, 2010;Trenberth, 2011).…”

“…As the clay fraction in the strata above and below the kaolinite pulse is dominated by smectite, it suggests some major change in climate and/or sediment supply occurs within the lower part of the PETM stratigraphy. Clay mineral assemblages have been used as indicators of palaeoclimate, most commonly using kaolinite as a proxy for humid tropical climates and smectite for warm climates with seasonal humidity and longer dry spells (Bolle et al, 2000;Thiry, 2000). However, soil formation is a slow process, and the subsequent long duration between formation and deposition in a marine basin suggests that clay mineralogy is an unreliable palaeoclimate proxy at resolutions shorter than 1 Myr (Thiry, 2000).…”

“…Clay mineral assemblages have been used as indicators of palaeoclimate, most commonly using kaolinite as a proxy for humid tropical climates and smectite for warm climates with seasonal humidity and longer dry spells (Bolle et al, 2000;Thiry, 2000). However, soil formation is a slow process, and the subsequent long duration between formation and deposition in a marine basin suggests that clay mineralogy is an unreliable palaeoclimate proxy at resolutions shorter than 1 Myr (Thiry, 2000). Changes in the clay mineral assemblage in the marine sediments is therefore unlikely to reflect an increase in continental soil production induced by changing temperatures and humidity (Carmichael et al, 2017).…”

On the need for (con) temporary utopias: Temporal reflections on the climate rhetoric of environmental youth movements

“…8For instance, this has been expressed in critique of the concept of the Anthropocene (e.g., Chakrabarty, 2009, 2018; Sörlin, 2018; Svensen et al, 2019). …”