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Nuclear Winter and the Anthropocene

Jon Spencer, Dept. of Geosciences, University of Arizona, Tucson, Arizona 85721, USA, Spencer7@arizona.edu

ABSTRACT Holocene (Crutzen, 2002). The “Great establish other boundaries within the geo-
In 2019, the Anthropocene Working Group Acceleration” of environmental change asso- logic time scale, including global synchro-
proposed the creation of an Anthropocene ciated with rapid post-WWII economic neity or near synchroneity (Waters et al.,
chronostratigraphic time unit to follow the growth and technological innovation (Steffen 2018). Although the beginning of the indus-
Holocene Epoch. The Anthropocene time et al., 2015) is now the leading candidate trial revolution was initially proposed as the
period would begin in the mid-twentieth for the beginning of the Anthropocene beginning of the Anthropocene (Crutzen
century, coincident with rapid acceleration (Anthropocene Working Group, 2019). The and Stoermer, 2000), the great accelera-
of multiple, ongoing anthropogenic changes Great Acceleration also coincides with hun- tion of anthropogenic environmental change
to Earth’s surface and environments. Radio- dreds of atmospheric nuclear-bomb tests, following WWII (Steffen et al., 2007, 2015)
active isotopes dispersed during the 1952– primarily by the United States and the Union led the Anthropocene Working Group to
1962 period of atmospheric thermonuclear- of Soviet Socialist Republics (USSR), that propose that an Anthropocene epoch begin
bomb tests form a proposed global marker injected radioisotopes into the global atmo- in the mid-twentieth century.
for the beginning of the Anthropocene. This sphere. Some of these isotopes will be mea-
marker is proposed for purely geological rea- surable in various materials for tens of thou- Radioisotope Fallout
sons as it is reasonably precise and global in sands of years, thus providing a geologic Explosive energy is derived entirely from
scope. These isotopes are also a marker for the marker for the beginning of the Anthro- nuclear fission in atomic bombs (“A-bombs”)
initiation of a new human capacity to trigger pocene (Waters et al., 2015). The purpose whereas an atomic bomb is the trigger for
global environmental change in a period of of this paper is to outline some of the envi- second-stage nuclear fusion in thermonu-
hours. The possibility of a global, multi- ronmental and geological consequences of clear bombs (“H-bombs”). Atmospheric
year nuclear winter following a nuclear war a major nuclear war as suggested by recent atomic-bomb tests dispersed radioactive fis-
between North Atlantic Treaty Organization studies in atmospheric sciences that indicate sion products to the troposphere where fall-
nations and Russia is suggested by recent the possibility of severe global cooling fol- out was largely confined to the general
studies of wildfires that injected sunlight- lowing such a war, a consequence termed region around the test site. In contrast, much
blocking smoke into the stratosphere, and by “nuclear winter” (e.g., Turco et al., 1983, larger thermonuclear weapon tests during
increasingly sophisticated numerical simula- 1990; Robock et al., 2007). Mid-twentieth- 1952–1962 (Fig. 1A) each produced a fireball
tions of global climate following a major century radioisotope fallout is not simply a that ascended into the stratosphere and
nuclear war. Although the proposal for an convenient marker for accelerated environ- resulted in global dispersal of radioisotopes
Anthropocene time period was made without mental change and a new geologic time (UNSCEAR, 2000). Two plutonium iso-
consideration of the consequences of nuclear period but indicates a new human capacity to topes in thermonuclear-bomb fallout, pluto-
war or nuclear winter, designating the period abruptly initiate catastrophic global change. nium-239 ( Pu) with a half-life of 24,110
239
of thermonuclear weapon tests as initiating years and plutonium-240 ( Pu) with a half-
240
an Anthropocene time period is supported THE BEGINNING OF life of 6563 years, will be identifiable in sedi-
here specifically because it indicates a new THE ANTHROPOCENE ment and ice for tens of thousands of years
human capability for rapid and destructive The International Commission on Stra- (Fig. 1B; Hancock et al., 2014).
environmental change on a global scale. tigraphy (ICS) defines and modifies units of Earth’s upper atmosphere is bombarded
the International Chronostratigraphic Chart with high-energy protons and atomic nuclei
INTRODUCTION (Cohen et al., 2013). In 2009, the ICS tasked derived from the Sun (“solar wind”) and
The Anthropocene is a proposed time the Subcommission on Quaternary Stra- from outside the solar system (“cosmic
period that would begin with geologic evi- tigraphy with forming an Anthropocene rays”) (Damon and Sternberg, 1989).
dence of human modifications of Earth’s sur- Working Group to study possible designa- Resulting nuclear reactions include trans-
face and environments, but with an unspeci- tion of a formal Anthropocene chronostrati- formation of nitrogen-14 ( N) to carbon-14
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fied future end date (Zalasiewicz et al., graphic time unit and to make recommen- ( C), which has a half-life of 5730 years.
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2019). The abundance and severity of such dations regarding modification of the This carbon promptly reacts with oxygen to
modifications since the industrial revolution geologic time scale. Consideration of a for- produce CO and is well mixed with the
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provoked consideration of an anthropic mal lower boundary for the Anthropocene atmosphere within a few years. Roughly
(human-related) time period following the requires conformity with criteria used to one in a trillion CO molecules in Earth’s
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GSA Today, v. 32, https://doi.org/10.1130/GSATG538A.1. CC-BY-NC.

4 GSA TODAY | August 2022