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Last chance at Durban? The geological dimension of climate change

Are we heading for the Miocene? US Government

DURBAN CLIMATE CHANGE CONFERENCE: Do the 10,000 or so delegates at Durban, and those whom they represent, fully accept that their mission constitutes no less than an attempt to reverse the suicidal course on which human civilisation has embarked? If they do, it is unlikely they would have had any hesitation in reaching decisions promoting an effective global mitigation effort.

Which begs the question: do they comprehend the magnitude of the current shift in state of the atmosphere-ocean system? Do they realise this is the largest-scale carbon oxidation event of the past 55 million years?¹

The atmosphere facilitates the carbon dioxide and oxygen cycles on which the biosphere depends. This can be compared to the role of the lungs in allowing the CO₂ and oxygen cycles of the human body. An excess or deficiency of these gases critically affects the behaviour of both the atmosphere-ocean system and of organisms.

Figure 1: Global temperature and greenhouse gas forcing (GHG) due to CO₂, CH₄ and N2O based on the Vostok ice core. The scale is expanded for the industrial era. Ratio of temperature and forcing scales is 1.5ºC per W/m², giving the slow feedback equilibrium response to GHG change and surface albedo change. Modern forcing include human-made aerosols, volcanic aerosols and solar irradiance. Hansen

The paleo-climate record allows high precision documentation of the history of the atmosphere-ocean system. Researchers can draw data from ice cores, sediments, coral reefs, cave deposits, fossil leaves and a wide range of proxies for ocean and land temperature, CO₂, salinity, dust and other climate-related parameters. They can look at the past to see what sort of future we may face. They can look at the past to study the behaviour of the atmosphere-ocean system and, through this, make observations regarding future trends.

The radiative forcing (energy level) of the atmosphere has risen by more than 3 Watt/m² (see Figure 1) due to greenhouse gases (CO₂, methane, nitrous oxide, ozone) and land clearing. This forcing exceeds previous interglacial atmosphere energy levels by more than 2 Watt/m² (Figure 1), translating to a more than 2°C increase in average global temperatures.

These studies suggest 21st century climate trends are tracking toward ice-free Earth conditions, like those that existed when atmospheric CO₂ levels exceeded 500 parts per million.

The Earth will pass between intermediate stages as it moves from glacial to greenhouse conditions. These would be analogous to peak Pliocene (about 3 million years ago) climates and peak Miocene (about 16 million years ago) climates, when temperatures were around 2 to 4°C higher than pre-industrial Holocene levels.

Figure 2 A. Development of radiative forcing 1880-2010 in terms of energy changes of greenhouse gases (CO₂, CH₄, N₂O, O₃), human emitted aerosols (mainly SO₂), volcanic eruptions, solar radiation and land use. B. Net variations in global energy levels (based on A). Hansen

Climate projections for the 21st century and beyond include the following considerations:

  • The current Earth–atmosphere energy balance (the difference between energy/heat absorbed from solar radiation and emitted back to space) is estimated at +3.2 Watt/m² relative to pre-industrial age conditions, correlated with a temperature rise of 2.3°C. This is a consequence of rising greenhouse gases, land clearing and fires (see Figure 2).

  • This temperature rise is currently masked by the approximately -1.1°C cooling effect of sulphur aerosols emitted from fossil fuel burning. Removing them would result in an abrupt temperature rise. The gradual temperature rise projections such as portrayed by the IPCC-AR4 do not portray the effect of sulphur aerosols.

  • We are now at 392 parts-per-million (ppm) of CO₂ in the atmosphere and 455 ppm CO₂-equivalent (including the effect of methane and nitrous oxide). The rise of CO₂ surpasses rates recorded from the past 55 million years. From past events, we know the atmosphere is sensitive to radiative forcing at levels currently approached.

  • As the large ice sheets continue to melt, we can expect transient cooling of sub-polar ocean regions. This could lead to collapse of the North Atlantic Thermohaline Current, with consequent abrupt cooling of Western Europe and North-east America.

  • Estimates of sea level rise depend on the melt rate of the Greenland and Antarctic ice sheets. The most reliable indication of the imminence of multi-metre sea level rise may be provided by empirical evaluation of the doubling time for ice sheet mass reported by Velicogna.

Climate change is increasingly expressed through the rise in frequency and intensity of extreme weather events around the world. The new IPCC-2011-AR5 draft report says we should expect higher and more frequent daily temperature extremes, and more frequent and intense heat waves. This is without taking the likelihood of tipping points into account.

The history of the atmosphere-ocean-cryosphere system and the extreme rate of greenhouse gas rise in the atmosphere suggest the likelihood of tipping points triggered by amplifying feedbacks, including opening of the Arctic Ocean, melting of ice sheets, release of methane from permafrost and lakes and forest fires.

Time to take things seriously. Andrew Glikson

The situation is now serious enough that some are considering further changes to the Earth’s atmosphere to minimise the effects of climate change.

Geo-engineering ideas aimed at averting tipping points in the climate system include two main approaches: solar shielding and CO₂ sequestration. Specifically, these include:

  • stratospheric sulphur injections: short-lived and destructive, acidify the ocean, retard the monsoon and disrupt precipitation over large parts of the Earth, including Africa, southern and south-east Asia
  • retarding solar radiation through space sunshades: short-lived, doesn’t prevent ocean acidification, but could be used to gain time for application of CO₂ draw-down
  • adding iron filings to the ocean as algal nutrients: likely ineffective in transporting CO₂ for storage in safe water depths
  • CO₂ sequestration using soil carbon, biochar and possible chemical methods such as “sodium trees”: if combined with rapid decline in industrial CO₂ emissions, can in principle help slow down and (if applied on a global scale) maybe reverse the current rise in atmospheric CO₂.

If the Durban meeting is serious about combatting climate change, it is time to look beyond half-formed attempts at mitigation. Budgets on a scale of military spending (>$20 trillion since World War II) would be required for any attempt to retard the current trend.

Top priority ought to be given to fast-track testing of soil carbon burial, biochar, chemical methods and serpentine-based sequestration. The conference must look at how to provide incentives for invention and development of new CO₂ sequestration methods.

It is likely a species which has succeeded in placing a man on the moon can also be successful in developing effective CO₂ sequestration methods. To do it, coordinated global efforts must be made and suitable funding has to be provided.

As stated by Joachim Schellnhuber, director of the Potsdam Climate Impacts Institute, “We’re simply talking about the very life support system of this planet”.


  1. Zachos et al., 2008. Nature, Vol 451, p 279–283; Zachos et al., 2001. Science, Vol 292, p 686–693; Glikson, 2008. Aust. Journal Australia Earth Science, 55, 125-140.

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