The Anthropocene

Today I want to present two articles by Steffen et al. (2007 and 2011), which give some background information on my topic geoengineering. They both deal with the Anthropocene, a term introduced about 10 years ago, describing the new era in Earth history which is strongly influenced by humans. The term is still not officially defined, but it generally describes the time until now where human influences on the Earth system became so strong and global in scale that they are able to modify the ‘great forces of Nature’ (Steffen et al. 2011: 843). The exact starting point of this time described as a new geological epoch is still discussed. Some scientists are of the opinion that clearing of forests 8000 years BP and first agriculture 5000 years BP are the first measurable human influences on e.g. the global carbon cycle. Human influence is also often linked to the extinctions of the Pleistocene megafauna. (Steffen et al. 2011)

However most scientist hold the opinion that the most determining factor for global changes in natural cycles is the industrialisation and the developments that followed. Whichever opinion is right, there are clear evidences for a strong human influence since the start of the Industrial Revolution 1700. The rise in atmospheric CO₂ is often taken as an indicator for human influence, as it is a result of fossil fuel use and other human activities e.g. deforestation  (Steffen et al. 2007 and 2011).

Due to the ability of natural carbon sinks to delay the response in CO₂ concentration in the atmosphere, the value for 1850 (285 ppm) is still within the natural variability of the Holocene. The human influence became visible later on: CO₂ concentration rose to 311 ppm in 1950, which is clearly beyond natural fluctuation (Steffen et al. 2007).

The time after 1950 is also described as the second stage of the Anthropocene or the Great Acceleration. The reason for this are the dramatic increases in the observed human impacts. ‘Every indicator of human activity underwent a sharp increase in rate around 1950’ (Steffen et al. 2011: 849). Changes can be seen e.g. in population, urban population, water use, transport or tourism:

source: Steffen et al. 2011, figure 1, p. 842

The same trends can be observed in natural cycles or events e.g. CO₂, N₂O and CH₄ concentrations in the atmosphere, flooding events or species extinctions:

source: Steffen et al. (2011), figure 1, p. 852

With those findings the human influence cannot be denied. The atmospheric CO₂ concentration reached 379 ppm in 2005 (Steffen et al. 2011), which is 102 ppm higher than the pre-industrial value of 1700. That means geoengineering techniques that aim so sequester CO₂ would have to deal with this amount of carbon dioxide, if we want to return to pre-industrial levels. 

The newer article from 2011 also highlights some points concerning geoengineering. It holds a rather critical view and reminds the reader, that side effects also have to be kept in mind. Steffen et al. (2011) chose the example of artificially added aerosols to illustrate the topic of geoengineering, but I don’t want to go into depth this time, as this is another technique that I want to present later in my blog. All in all the authors stress that further research is still needed before a decision on geoengineering can be made. In addition there are ethical, social and organisational/governmental questions that still need to be answered (Steffen et al. 2011).

Literature:

Steffen, W., Crutzen, P. and McNeill, J. (2007) ‘The Anthropocene: Are Humans Now Overwhelming the Great Forces of Nature?’, AMBIO, 36 (8), 614 – 621.
available online: http://www.bioone.org/doi/abs/10.1579/0044-7447(2007)36%5B614:TAAHNO%5D2.0.CO;2

Steffen, W., Grinevald, J., Crutzen, P. and McNeill, J. (2011) ‘The Anthropocene: conceptual and historical perspectives’, Philosophical Transactions of The Royal Society, 369, 842-867.
available online: http://rsta.royalsocietypublishing.org/content/369/1938/842.short