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Tipping points near
No alternative to atmospheric CO2 draw-down
The scale and rate of modern climate change have been underestimated. The release to date of a
total of over 500 billion ton (GtC) of carbon through emissions, land clearing and fires, has
raised CO2 levels to 397-400 ppm and near 470 ppm CO2-e [a value including methane] at a rate
of ~2 ppm CO2 per year [1] (Figures 1 and 2). These developments are shifting the Earth’s
climate toward Pliocene-like (5.2 – 2.6 million years-ago [Ma]; +2-3oC) conditions and possibly
mid-Miocene-like (~16 Ma; +4oC) conditions [2], within a couple of centuriesa geological
blink of an eye.
The current CO2 level generates amplifying feedbacks from the ice/water transformation and
albedo loss, methane release from permafrost, methane clathrates and bogs, from droughts and
loss of vegetation cover, from fires and from reduced CO2 sequestration by warming water.
With CO2 atmospheric residence times in the order of thousands to tens of thousands years [3],
protracted reduction in emissions, either flowing from human decision or due to reduced
economic activity in an environmentally stressed world, may no longer be sufficient to arrest the
feedbacks.
Four of the large mass extinction events in the history of Earth (end-Devonian, Permian-Triassic,
end-Triassic, K-T boundary) have been associated with rapid perturbations of the carbon, oxygen
and sulphur cycles, on which the biosphere depends, at rates to which species could not adapt
[4].
Since the 18th century, and in particular since about 1975, the Earth system has been shifting
away from Holocene (10,000 years to the present) conditions, which allowed agriculture,
previously not possible due to instabilities in the climate and extreme weather events. The shift is
most clearly manifested by the loss of polar ice [5] (Figure 3). Sea level rises have been
accelerating, with a total of more than 20 cm since 1880 and about 6 cm since 1990 [6] (Figure
4).
For temperature rise of 2.3oC, to which the climate is committed if sulphur aerosol emission
discontinues (see Figure 1), sea levels would reach Pliocene like levels of 25+/-12 meters, with
lag effects due to ice sheet hysteresis.
With global CO2 levels at 400 ppm, the upper stability limit of the Antarctic ice sheet, current
rate of CO2 emissions from fossil fuel combustion, cement production, land clearing and fires of
~9.7 GtC in 2010 [7] , global civilization is at a tipping point, facing the following alternatives:
1. With carbon reserves sufficient to raise atmospheric CO2 levels to above 1000 ppm
(Figure 5), continuing business-as-usual emissions can only result in advanced melting of
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the polar ice sheets, a corresponding rise of sea levels on the scale of meters to tens of
meters and continental temperatures rendering agriculture unlikely.
2. With atmospheric CO2 at ~400 ppm, abrupt decrease in carbon emissions may no longer
be sufficient to prevent current feedbacks (melting of ice, methane release from
permafrost, fires). Attempts to stabilize the climate would require global efforts at CO2
draw-down, using a range of methods including global reforestation, extensive biochar
application, chemical CO2 sequestration (using sodium hydroxide, serpentine and new
innovations) and burial of CO2 [8]
As indicated in Table 1, the use of short-term solar radiation shields such as sulphur aerosols
cannot be regarded as more than a band aid, with severe deleterious consequences in terms of
ocean acidification and retardation of the monsoon and of precipitation over large parts of the
Earth. Retardation of solar radiation through space sunshades is of limited residence time and
would not prevent further acidification from ongoing carbon emission.
Dissemination of ocean iron filings aimed at increasing fertilization by plankton and algal
blooms, or temperature exchange through vertical ocean pipe systems, are unlikely to be
effective in transporting CO2 to relatively safe water depths.
By contrast to these methods, CO2 sequestration through fast track reforestation, soil carbon,
biochar and possible chemical methods such as “sodium trees” and serpentine (combining Ca
and Mg with CO2) (Figure 6) may be effective, provided these are applied on a global scale,
requiring budgets on a scale of military spending (>$20 trillion since WWII).
Urgent efforts at innovation of new CO2 draw-down methods are essential. It is likely that a
species which decoded the basic laws of nature, split the atom, placed a man on the moon and
ventured into outer space should also be able to develop the methodology for fast sequestration
of atmospheric CO2. The alternative, in terms of global heating, sea level rise, extreme weather
events, and the destruction of the world’s food sources is unthinkable.
Good planets are hard to come by.
Andrew Glikson
Earth and paleoclimate science.
3 December, 2012
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[1] IPCC AR4 http://www.ipcc.ch/ ; Global Carbon Project http://www.globalcarbonproject.org/
; State of the planet declaration http://www.planetunderpressure2012.net/
[2] Zachos, 2001 cmbc.ucsd.edu/content/1/docs/zachos-2001.pdf; Beerling and Royer, 2011
http://www.nature.com/ngeo/journal/v4/n7/fig_tab/ngeo1186_ft.html; PRISM USGS Pliocene
Project http://geology.er.usgs.gov/eespteam/prism/
[3] Eby et al., 2008. geosci.uchicago.edu/~archer/reprints/eby.2009.long_tail.pdf
[4] Keller, 2005; Glikson, 2005; Ward, 2007. http://www.amazon.com/Under-Green-Sky-
Warming-Extinctions/dp/B002ECEGFC#reader_B002ECEGFC
[5] Loss of polar ice http://www.agu.org/pubs/crossref/2011/2011GL046583.shtml
[6] CLIM 012 Assessment Nov 2012; http://www.eea.europa.eu/data-and-maps/indicators/sealevel-
rise-1/assessment, Rahmstorf et al., 2012, http://iopscience.iop.org/1748-
9326/7/4/044035/article.
[7] Raupach, 2011, www.science.org.au/natcoms/nc-ess/documents/ GEsymposium.pdf)
[8] Geo-engineering the Climate? A Southern Hemisphere perspective. AAS conference
www.science.org.au/natcoms/nc-ess/documents/GEsymposium.pdf
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Figure 1.
Part A. Mean CO2 level from ice cores, Mouna Loa observatory and marine sites;
Part B (inset). Climate forcing 1880 – 2003 (Hansen et al., 2011)
http://pubs.giss.nasa.gov/abs/ha06510a.html . Aerosol forcing includes all aerosol effects,
including indirect effects on clouds and snow albedo. GHGs include O3 and stratospheric H2O,
in addition to well-mixed GHGs.
.
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Figure 2.
Relations between CO2 rise rates and mean global temperature rise rates during warming periods,
including the Paleocene-Eocene Thermal Maximum, Oligocene, Miocene, glacial terminations,
Dansgaard-Oeschger cycles and the post-1750 period.
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Figure 3
Greenland (a) and Antarctic (b) mass change deduced from gravitational field measurements by
Velicogna (2009) http://pubs.giss.nasa.gov/abs/ha05510d.html
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Figure 4
From Rahmstorf et al., 2012. Sea level measured by satellite altimeter (red with linear trend line;
AVISO data from (Centre National d’Etudes Spatiales) and reconstructed from tide gauges
(orange, monthly data from Church and White (2011)). Tide gauge data were aligned to give the
same mean during 1993–2010 as the altimeter data. The scenarios of the IPCC are again shown
in blue (third assessment) and green (fourth assessment); the former have been published starting
in the year 1990 and the latter from 2000. http://iopscience.iop.org/1748-9326/7/4/044035/article
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Figure 5.
CO2 emissions by fossil fuels (1 ppm CO2 ~ 2.12 GtC). Estimated reserves and potentially
recoverable resources are from Energy Information Administration (2011) and the German
Advisory Council on Climate Change (2011). From Hansen 2012
www.columbia.edu/~jeh1/mailings/…/20120130_CowardsPart2.pdf
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Figure 6
A schematic representation of various geoengineering and carbon storage proposals.
Diagram by Kathleen Smith/LLNL
https://www.llnl.gov/news/newsreleases/2008/NR-08-05-04.html
