By Andrew Glikson, Canberra Regional Meeting.


The current atmospheric carbon dioxide (CO2) level is already triggering amplifying feedbacks from the Earth system. Consequently, efforts at reducing atmospheric CO2 emissions are no longer sufficient in themselves to prevent further global warming. For this reason, along with sharp reductions in carbon emissions, efforts are needed to attempt to reduce atmospheric CO2 levels from their current level of near 400 parts per million (ppm) to well below 350 ppm. Outer-space shade technology applied by NASA may buy time for such planetary defence effort.

The scale and rate of modern climate change have been greatly under-estimated. The release to date of a total of over 560 billion tonnes of carbon through emissions from industrial and transport sources, land clearing and fires, has raised CO2 levels from about 280 parts per million (ppm) in pre-industrial periods to 397-400 ppm and near 470 ppm CO2-equivalent (a value which includes the CO2-equivalent effect of methane). The level of CO2 is currently increasing at about 2 ppm per year1 (see Figures 1 and 2).

These developments are shifting the Earth’s climate towards that in the Pliocene epoch 5.2–2.6 million years ago, when the mean global temperatures were 2–3°C above pre-industrial temperatures. It may possibly approach that of the mid-Miocene epoch approximately 16 million years-ago, with mean global temperatures 4°C above pre-industrial temperatures2. This could happen within a few centuries – a geological blink of an eye.

The current CO2 level generates feedbacks that increase its effects. Warmer water has a reduced capacity to absorb CO2 from the atmosphere; fires, droughts and loss of vegetation cover increase CO2 release; methane is released from bogs, permafrost and methane-bearing ice particles and methane-water molecules.

Once CO2 gets into the atmosphere, it will stay there for thousands to tens of thousands years, so protracted reduction in emissions, either from human decision or due to reduced economic activity in an environmentally stressed world, may no longer be sufficient to stop the feedbacks.

Four of the large mass extinction of species events in the history of Earth (the end of the Devonian 359 million years ago, the Permian-Triassic boundary 252 million years ago, the end of the Triassic 201 million years ago, and the K-T boundary 66 million years ago) have been associated with rapid disturbances of the carbon, oxygen and sulphur cycles, on which the biosphere depends, at rates to which species could not adapt4.

Since the 18th century, and in particular since about 1975, the Earth system has been shifting away from Holocene (approximately 10,000 years to the pre-industrial time) conditions, which allowed agriculture, previously hindered by instabilities in the climate and by extreme weather events. The shift is most clearly manifested by the loss of polar ice5. Sea level rises have been accelerating, with a total rise of more than 20 cm since 1880 and about 6 cm since 19906.

Global temperatures are reduced by sulphur aerosols from volcanoes and similar sources. If these emissions were to stop, the global temperature would rise by 2.3°C as a consequence of the greenhouse gases already in the atmosphere (see Figure 1)7. As a result, sea levels would rise between 13 and 37 metres, levels experienced in the Pliocene epoch.

The current global atmospheric CO2-equivalent of above 470 ppm is just under the upper stability limit of the Antarctic ice sheet8. With current rate of CO2 emissions from fossil fuel combustion, cement production, land clearing and fires of about 9.7 billion ton of carbon in 20109, global civilisation faces the following alternatives:

1. With carbon reserves sufficient to raise atmospheric CO2 levels to above 1000 ppm10, continuing business-as-usual emissions can only result in advanced melting of the polar ice sheets, a corresponding rise of sea levels on the scale of metres to tens of metres, on a time scale of decades to centuries, and high to extreme continental temperatures rendering agriculture and human habitat unlikely over large regions11.

2. With atmospheric CO2 at about 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 stabilise the climate 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), as well as burial of CO212.

As indicated in Table 1, Solar radiation screens have been investigated to reduce the amount of solar radiation reaching the earth. Screens of aerosols of materials such as sulphur dioxide offer only band-aid solutions, as they remain in the atmosphere only a couple of years. These chemicals also lead to serious ocean acidification, and interfere with rainfall patterns such as the monsoons.

By contrast, retardation of solar radiation through space sunshade technology may allow time for CO2 draw-down. One suggested method (put forward by the appropriately named Professor Angel)would involve the launch of trillions of small discs into orbit between the sun and the earth to deflect solar radiation around the Earth13. Unlike sulphur dioxide injections, this will not acidify the ocean, but would require a massive project for which only NASA would have the resources.

Oceanic plankton and algal blooms can absorb large amounts of carbon, but are largely restricted because of the lack of iron in the ocean. Experiments have been conducted in which iron filings have been added to the ocean14, but results have been variable. It is not known how long the captured carbon will be held in the ocean depths, or what the other effects on the ocean’s ecology might be. Also, temperature exchanges through vertical ocean pipe systems are unlikely to constitute effective means of transporting CO2 to relatively safe water depths.

In contrast to these methods, CO2 sequestration through well understood methods such as fast track reforestation, increase in soil carbon, bio-char, and possibly by chemical methods such as “sodium trees” (which combine carbon dioxide with sodium hydroxide to form sodium carbonate or bicarbonate) and serpentine (combining calcium and magnesium with CO2)15 may be effective, provided these are applied on a global scale and the captured carbon can be stored securely.

Such efforts will require an effective planetary defence effort on the scale currently expended on military spending (totalling more than $20 trillion since WWII).

Surely a species which has 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.


Figure 1.

Part A. Mean CO2 level from ice cores, Mouna Loa observatory and marine sites; Part B (inset). Climate forcing 1880 – 2003 ( Aerosol forcing includes all aerosol effects, including indirect effects on clouds and snow albedo. GHGs include ozone (O3) and stratospheric H2O, in addition to well-mixed greenhouse gases (



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. (



1. ; ;

2. ;

3. ;

4. Extinctions/dp/B002ECEGFC#reader_ B002ECEGFC ; mass-extinction-event-on-the-way-5397 ; 1118.html












Share This