Welcome to the Anthropocene?

An international team of geologists is proposing that since the Industrial Revolution humankind has so changed the earth that it has brought about an end to one epoch of earth’s history and marked the start of another. They believe that human dominance has so physically altered the earth itself that the Holocene epoch has ended and we have entered a new epoch - the Anthropocene.

In the open access article "Are we now living in the Anthropocene?", published in the journal GSA Today, the scientists examined phenomena such as changes in the patterns of sediment erosion and deposition, major disturbances to the carbon cycle and global temperature, ocean acidification and wholesale changes to the world’s plants and animals.

Human activity has become the number one driver of most of the major changes in Earth's topography and climate. You can’t have 6.5 billion people living on a planet the size of ours and exploiting every possible resource without creating huge changes in the physical, chemical and biological environment which will be reflected dramatically in our geological record of the planet. - Dr Andrew Gale, School of Earth and Environmental Sciences, University of Portsmouth

The Holocene epoch the researchers think is now ending, is a geological period which began approximately 11,550 years ago. It is part of the Neogene and Quaternary periods and can be considered as an interglacial in the current ice age. In 2002, Paul Crutzen, a Nobel Prize–winning chemist, however suggested that we had left the Holocene and had entered a new Epoch — the Anthropocene — because of the global environmental effects of increased human population and economic development.

Members of the Stratigraphy Commission of the Geological Society of London now amplify and extend the discussion of the effects referred to by Crutzen and then apply the same criteria used to set up new epochs to ask whether there really is justification or need for a new term, and if so, where and how its boundary might be placed. In their paper, the scientists present the scholarly groundwork for consideration by the International Commission on Stratigraphy for formal adoption of the Anthropocene as the youngest epoch of, and most recent addition to, the earth's geological timescale.

Human influence altering the Holocene
Prior to the Industrial Revolution, the global human population was some 300 million at A.D. 1000, 500 million at A.D. 1500, and 790 million by A.D. 1750 and exploitation of energy was limited mostly to firewood and muscle power. Early to mid-Holocene increases in atmospheric carbon dioxide ranged from 260 to 280 ppm, a factor in the climatic warmth of this interval, the result of forest clearance by humans. Human activity was not absent in the creation of Holocene strate, but it did not create new, global environmental conditions that could translate into a fundamentally different stratigraphic signal.

In contrast, from the beginning of the Industrial Revolution to the present day, global human population has climbed rapidly from under a billion to its current 6.5 billion (Fig. 1, click to enlarge), and it continues to rise. The exploitation of coal, oil, and gas in particular has enabled planet-wide industrialization, construction, and mass transport, the ensuing changes encompassing a wide variety of phenomena, which can be summarised under the following headings:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: agriculture :: biodiversity :: climate change :: fossil fuels :: population :: geology :: Holocene :: Anthropocene ::

Changes to Physical Sedimentation
Humans have caused a dramatic increase in erosion and the denudation of the continents, both directly, through agriculture and construction, and indirectly, by damming most major rivers, that now exceeds natural sediment production by an order of magnitude.

Carbon Cycle Perturbation and Temperature
Carbon dioxide levels (379 ppm in 2005) are over a third higher than in pre-industrial times and at any time in the past 0.9 million years. Conservatively, these levels are predicted to double by the end of the twenty-first century. Methane concentrations in the atmosphere have already roughly doubled. These changes have been considerably more rapid than those associated with glacial-interglacial transitions. Global temperature has lagged behind this increase in greenhouse gas levels, but temperatures in the past century rose overall, with the rate of increase accelerating in the past two decades. Temperature is predicted to rise by 1.1 °C to 6.4 °C by the end of this century, leading to global temperatures not encountered since the Tertiary.

Biotic Change
Humans have caused extinctions of animal and plant species, possibly as early as the late Pleistocene, with the disappearance of a large proportion of the terrestrial megafauna. Accelerated extinctions and biotic population declines on land have spread into the shallow seas, notably on coral reefs. The current rate of biotic change may produce a major extinction event. The projected temperature rise will certainly cause changes in habitat beyond environmental tolerance for many taxa.

The effects of these temperature changes will be more severe than in past extinction waves because, with the anthropogenic fragmentation of natural ecosystems, “escape” routes are fewer.

The combination of extinctions, global species migrations, and the widespread replacement of natural vegetation with agricultural monocultures is producing a distinctive contemporary biostratigraphic signal. These effects are permanent, as future evolution will take place from surviving (and frequently anthropogenically relocated) stocks. - Jan Zalasiewicz, et. al.

Sea-level change
Pre-industrial mid- to late Holocene sea-level stability has followed a 120m rise from the late Pleistocene level. Slight rises in sea level have been noted over the past century, ascribed to a combination of ice melt and thermal expansion of the oceans. The rate and extent of near-future sealevel rise depends on a range of factors that affect snow production and ice melt. In its latest report, the IPCC predicted a 0.19–0.58 m rise by 2100.

This prediction however does not factor in recent evidence of dynamic ice-sheet behavior and accelerating ice loss possibly analogous to those preceding “Heinrich events” of the late Pleistocene and early Holocene, when repeated episodes of ice-sheet collapse caused concomitant rapid sea-level rise. Current predictions are short-term, while changes to the final equilibrium state may be as large as a 10–30 m sea-level rise per 1 °C temperature rise.

Ocean acidification
Relative to pre-Industrial Revolution oceans, surface ocean waters are now 0.1 pH units more acidic due to anthropogenic carbon release. The future amount of this acidification, scaled to projected future carbon emissions, its spread through the ocean water column, and its eventual neutralization (over many millennia) has been modeled: projected effects will be physical (neutralization of the excess acid by dissolution of ocean-floor carbonate sediment, hence creating a widespread non sequence) and biological (hindering carbonate-secreting organisms in building their skeletons), with potentially severe effects in both benthic (especially coral reef) and planktonic settings.

The sensitivity of climate to greenhouse gases, and the scale of (historically) modern biotic change, makes it likely that we have entered a stratigraphic interval without close parallel in any previous Quaternary interglacial. - Jan Zalasiewicz, et. al.

The scientists conclude that the Anthropocene might evolve into a “super-interglacial” , with Earth reverting to climates and sea levels last seen in warmer phases of the Miocene or Pliocene, most likely achieved via a geologically abrupt rearrangement of the ocean-atmosphere system. Such a warm phase will likely last considerably longer than normal Quaternary interglacials. It is not clear that an equilibrium comparable to that of pre-industrial Quaternary time will eventually resume, they write.

Figure: Comparison of some major stratigraphically significant trends over the past 15,000 yr. Trends typical of the bulk of immediately pre-Holocene and Holocene time are compared with those of the past two centuries. Credit: Zalasiewicz J, et al., GSA Today.

References:
Zalasiewicz J, Williams M, Smith A, Barry TL, Coe AL, et al. (2008), "Are we now living in the Anthropocene", GSA Today: Vol. 18, No. 2 pp. 4–8

AlphaGalileo: Man's impact on the planet brings about new epoch in earth's history - January 31, 2008.