How far and how fast?
The critical issue of speed and scale-
illustrated by the case of global warming.

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Philip Sutton
Director, Policy and Strategy
Green Innovations Inc.
Tel & fax: +61 3 9486 4799
29 March  2001 Version 1.v/w:iii

Paper marked up in HTML format
by Philip Sutton.




If we are to achieve ecological sustainability,
at what level should we stabilise greenhouse gases in the atmosphere?

The International Framework Convention on Climate Change, signed in 1992, binds member countries to stabilise greenhouse gas "concentrations at levels preventing a dangerous human interaction with the climate". If we consider the needs of both humans and other species, then it is argued that a dangerous level of emissions would be a level that prevents the achievement of ecological sustainability.

The achievement of ecological sustainability in turn depends on reducing the extinction rate[1] to a 'natural' level, that is, the rate experienced between the mass extinction events caused by natural mega-disasters such as major meteor strikes and ice ages[2]. The current extinction rate is thought to be at least 100-1000 times this target rate (Pimm et al., 1995).

What then is an atmospheric CO2 level compatible with a natural extinction rate? We do not have the data to answer this definitively but the safest guess is that it will be a level that is within the band of CO2 concentrations experienced by the planet in the period that has been 'formative' in terms of recent biological and geomorphological evolution.

We now know that atmospheric CO2 levels ranged between 300 ppmv (related to the warmest, natural,  inter-glacial periods) and 170 ppmv (related to the coldest, natural, glacial periods) over the last 420,000 years (Petit et al., 1999) - see Figure 1 - and was under 500 ppmv, and most probably under 400 ppmv for the whole of the last 23 million years[3] (Pearson &  Palmer, 2000) - see Figure 4. It would not be surprising if many species and ecosystems were not adapted to cope with conditions outside this range of evolutionary experience.  And yet that is the domain we are moving into with the CO2 concentration in the atmosphere predicted to reach between:

The concentration of atmospheric CO2 has now reached 368 ppmv (Brown, 2000) which is about 30% higher than the pre-industrial level of 280 ppmv, and is a 16% gain in the four decades from 1960.  The current CO2 level is also about 20% higher than the highest level experienced by the planet in the past 420,000 years (Petit, 1999).  Indeed the atmospheric concentration of CO2 may well be the highest for some 20 million years (Pearson &  Palmer, 2000).  This time span is so great that it is fair to say that few living organisms would possess adaptive characteristics for coping with environmental conditions caused by atmospheric CO2 levels much over 300 ppmv, where these characteristics are an evolutionary legacy of an earlier time of elevated CO2.


Figure 1: Vostok (1987 data)
The data shows a surprisingly close correlation during the last 160,000 years between CO2 concentrations and average temperatures on earth as established by chemical and isotopic analysis of ‘fossil air’ enclosed in Antarctic ice. (Source: von Weizsäcker et al., 1997 p. 226. Drawing by Global Commons Institute, London, after Jouzel et al., 1987.)

Figure 2: Vostok (1987 data) plus the present

From the Shell website:
Source page:,5028,25813-51353,00.html
Diagram URL:

The Shell diagram (Figure 2) shows the massive increase in atmospheric CO2 in the last 50 years and the expected continuation of the trend.

Following the release of the Vostok data in 1987 a collaborative, international research program involving Russia, the U.S. and France was deployed from 1989 to 1998 to continue the data into the deep past. In 1999 the atmospheric CO2 and temperature data were published for the last 420,000 years - see Figure 3.

Figure 3: Vostok 1999 - The last 420,000 years.

From the U.S. Global Change Research Program website:
Source page:
Graph at URL:
Definitive source: Petit, 1999  (reproduced here with the graph flipped to place the past on the left/present on the right)

This data shows that over 4 long climate cycles atmospheric CO2 has never gone over 300 ppmv and that the picture painted by the early Vostok data, based on one long climate cycle, was not an aberration. Indeed there is strong evidence that the atmospheric CO2 level has been under 400 ppmv for the last 23 million years (Pearson &  Palmer, 2000) - see Figure 4.

Figure 4: estimated atmospheric CO2 levels over the last 25 million years

From: Pearson & Palmer, 2000 (reproduced here with the graph flipped to place the past on the left/present on the right)
(The vertical and horizontal bars in the graph represent the confidence limits of the data.)

If atmospheric CO2 is to be reduced to a precautionary 300 ppmv or less,
how much do human-caused emissions to the atmosphere need to be reduced?

If we are to bring the atmospheric CO2 level below 300 ppmv how much will we need to reduce emissions caused by human activity? We do not have data to answer this question precisely. However the CSIRO[4] has published information about one scenario which throws useful light on the issue.

The CSIRO (Enting et al., 1994), as part of their contribution to the Intergovernmental Panel on Climate Change Special Report on "Radiative forcing of Climate change"-1994, coordinated a global collaborative modelling exercise which examined five scenarios in which atmospheric CO2 was stabilised at levels ranging from 350 ppmv to 750 ppmv (see Figure 5). Simulation results were then obtained for each of the scenarios from 10 carbon cycle models operating in various parts of the world. The scenario closest to our precautionary target of 300 ppmv (or less) was the 350 ppmv scenario (see Figure 6 - S350).

Figure 5: Scenarios for the stabilisation of atmospheric CO2

Source: Enting et al. (1994) p.26

Figure 6: Industrial emissions profiles for a stabilisation of atmospheric CO2 at 350 ppmv, generated by ten different climate models used around the world.

Source: Enting et al. (1994) p.102

According to 8 out of 10 of the world climate models, to stabilise CO2 in the atmosphere at 350 ppmv (NB: which is most likely too high by at least 50 ppmv. if ecological sustainability is to be achieved) it will be necessary to:

The need to sequester (remove from the atmosphere and store) very large quantities of CO2 that have already been released into the atmosphere as a result of human activity, suggests that current programs to use carbon sinks as off-sets against new CO2 emissions are inappropriate. It would make more sense to use all sinks to sequester past emissions.

This zero CO2 emissions target is hugely more demanding than the 20% reduction 1988 Toronto Target and the much lower target adopted for the developed world at Kyoto in 1997 (5.2% reduction from the 1990 level)[5]. It is also much more than the apparently radical 60% reduction that the Intergovernmental Panel on Climate Change (1994) said would be necessary if the levels of greenhouse gases in the atmosphere were to be stabilised at 1990 levels.


The need for action

Given the magnitude of the change required to bring atmospheric CO2 to 350 ppmv (ie. achieving a zero emission of CO2 as a result of human economic activity, with a major program to remove excess CO2 already in the atmosphere), is it worth making the effort?

When making up our minds on this it is worth remembering that:

If the rate of greenhouse warming is accelerating as suggested by Karl et al. ( 2000) and, if this apparent new trend continues, then it compounds the urgency of  dealing with the greenhouse issue[8].


How fast

Hare (undated/~1997) argues that if dangerous climate effects are to be avoided that a limit must be set to the amount of additional CO2 that is released to the atmosphere.  This places a cap on the quantity of fossil fuels that can be burned during the 21st century.

Drawing on the WMO/ICSU/UNEP Advisory Group on Greenhouse Gases (AGGG)  reported in Rijsberman & Swart (eds.) (1990)  and more recent assessments, Hare set the following limits on environmental change in order to "prevent dangerous anthropogenic interference with the climate system".

Sea level rise: 
maximum rate of rise of 20 - 50mm per decade 
maximum total rise of 0.2 - 0.5 metres above 1990 global mean sea level 

Global mean temperature: 
maximum rate of increase of 0.1°C per decade 
maximum total increase of 1.0°C 

Based on these limits it is argued (probably too generously given that atmospheric CO2 levels already exceed the precautionary 300 ppmv (or less) level argued by this paper) that the amount of additional carbon (in the form of CO2) that could still be added to the atmosphere is 225 Giga-tonnes.  This represents about one quarter of the currently proven economic reserves of fossil fuels. At the historic rates of increase in fossil fuel use, this 225 Gt "carbon budget" will be exhausted by 2020.  To avoid releasing more than this "carbon budget" it would be necessary to phase out the use of fossil fuels altogether.

This paper argues that, given the huge inertia in the energy production and consumption systems, that is, in the structure of the economy and in the patterns of behaviour in the society, a phasing out of fossil fuels in their entirety could easily take 20 years and would normally be expected to take significantly longer.  So if we are to avoid using up or exceeding the remaining "carbon budget" proposed by Hare, then we need to begin the phase-out of fossil fuels immediately. It is likely that the maximum time available for the transition, if the carbon budget is not to be exceeded, is about 25 years.  This is an exceptionally short time in which to accomplish such a major change, although in wartime changes of this magnitude have been made in the past.

Figure 7: Hypothetical fossil fuel phase-out curve.




It would seem that action at a massive scale is needed very urgently if we are to avoid major ecological disruptions and the possibility of destabilising human societies and economies.  It seems that the answers to the questions "how far?" and "how fast?" posed in the title to this paper are crudely:

If greenhouse gas emissions from the economy need to brought down to zero, fossil fuel use would need to be brought down to zero too unless the CO2 produced in the process of energy production could be trapped and stored.  For example there is currently consideration being given to injecting CO2 into deep geological structures. 

The notion of phasing out the use of fossil fuels, possibly in their entirety, was recently examined by the UK Royal Commission on Environmental Pollution (Blundell et al., 2000).  While the Commission's recommendations fell significantly short of what is suggested in this paper it did recommend in June 2000 that:

So it is clear that major changes to the economy in order to deal with the greenhouse issue are under consideration in official circles in at least parts of the world.


Where to from here?

The intention behind writing this paper is not to distress or alarm people. The purpose is simply to get as realistic as possible an idea of the task before us if we are to create a sustainable world.

There needs to be debate about whether the conclusions of this paper are right[9]. Do we need to pursue a 'zero greenhouse gas emissions' policy and do we need to make a quick 100% switch from the use of fossil fuels? We will, in due course, link a web page to provide a forum for this debate.

We also need to look at the opportunities for finding solutions that are equal to the problem. Another web page with links to such solutions will also be added.

And then we need to take effective action.

Amory Lovins made the following comment on an earlier version of this paper:

Conclusion may be true for all we know. However, an all-efficiency-and-renewables/benign-sources future is neither costly nor unrealistic. In fact, it may be cheaper in private internal cost than conventional climate-damaging futures. See, which offers extensive examples of very large resource savings' costing less (making more profit) than small or no savings. We ought to be going in that direction regardless of how the climate science turns out, just to save/make money. -- ABL (9 Aug 2000)
You can find the full text of "Natural Capitalism", Paul Hawken's & Amory and Hunter Lovins' book at:

The book outlines an approach to the economy and business, and gives a great many practical examples, that may well be equal to the task suggested in this paper.

Another very significant resource is the recent book Sustainable Technology Development by Weaver et al. (2000). This book reports on the Dutch program of the same name aimed at developing technologies that will enable society to actually achieve sustainability - and it outlines the methodologies used.

The issue of whether economic change of the speed and scale suggested in this paper would cripple or enhance the economy is discussed in another Green Innovations web page, Greenhouse response: an opportunity for economic renewal.

A note, in .RTF format, giving some insight into how to use 'stretch goals' such as stabilising atmospheric CO2 at (or below) 300 ppmv or cutting CO2 emissions from the economy effectively to zero in about 25 years can be downloaded from this page.



1. And ensuring that the speciation rate is not less than the 'natural' rate. If extinction rates fall but speciation rates are zero then the evolutionary process is not sustained. Frankel and Soulé (1981) believe that larger, longer lived vertebrates and vascular plants face a zero speciation future.

2. Or the invasion of habitats by humans with cultures not adapted to the maintenance of ecological sustainability in the local context (Flannery, 1994).

3.  The confidence limits of the current data do not permit a completely unequivocal conclusion.

4. Australia's largest public scientific research organisation.

5. Personal communication from Geoff Holland (Institute of Global Futures Research) August 2000:
The Kyoto 5.2% reduction target does not refer to global emissions but Annex B countries emissions. The targets, if met, would constitute about 4.5% of world emissions should the developing world not increase emissions. If the developing world does increase emissions (quite possible), then the Kyoto reductions will be even less. Most Annex B countries are not on course to meet their target. Growth in international bunker fuels emissions is likely to increase also, further reducing significance of Kyoto targets.

Global emissions have stabilised at 6.3GtC 1996, 1997, 1998 even reduced a little in 1999. This is likely due to slower economic growth in most economies with the notable exception of the US. Such a plateau and slight drop was also experienced in 1981, 1982, 1983 as well as in 1992 and 1993 (before another rise).

6. But under stabilisation at 550 ppm, this loss is substantially reduced, even by the 2230s.

7. The results of modelling the global climate and ocean systems by the Australian Government's Division of Atmospheric Research (a branch of the CSIRO) suggest that:
* if the atmospheric carbon dioxide level reaches between two and three times the natural level (that is between 550 and 800 parts per million by volume) the atmosphere will heat up so much that much less sea ice will be formed in the Antarctic and the Arctic.
* when sea ice forms the salt is 'squeezed' out (which is why sea ice is fresh) and this extra salt makes the surface water heavier and as a consequence it sinks to the bottom of the ocean.
* the formation of extra-salty water normally happens on such a huge scale that the sinking water sets up a global circulation of water from the polar region to the equator and back again (the thermohaline circulation).
* if greenhouse gas emissions keep going at the rates realistically expected the atmosphere will heat up enough to greatly reduce sea ice formation and therefore enough to shut off the thermohaline circulation and this shut off is expected to happen within 150 years according to the model results.
* since it is the thermohaline circulation that brings oxygen from the atmosphere to the deep ocean, the oceans will stagnate and hydrogen sulphide will slowly build up, eventually killing oxygen-dependent life in the oceans below about 1-1.5 km (as demonstrated by the Black Sea where there is no deep circulation) - wind driven circulation will continue to aerate most oceans above the depth of 1-1.5 km.
(This argument is informed by a personal communication from Dr Peter Whetton, 2000.)
The modelling results are reported in Hirst (1999).

8.    The Intergovernmental Panel on Climate Change (1996) projected that the rate of global warming in the 21st century would be between two and six degrees Fahrenheit. However Thomas Karl and his associates at the National Climate Data Center (Karl et al., 2000) have analysed climate data from recent years and concluded that global warming since 1976 has been occurring at a rate of four to five degrees Fahrenheit per century - significantly above the warming rates prior to that .  Hansen et al. (2000) believe that greenhouse gases other than CO2 (eg. methane, CFCs, tropospheric O3, N20, etc.) have been the main cause of the acceleration and that future emissions of these gases are unlikely to cause a continuation of the acceleration.

9. For example, some people believe that the threat from greenhouse warming is either modest or non-existent (see John Daly's website).



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Brown, L  (2000). "Climate change has world skating on thin ice". Worldwatch Issue Alert #7 - August 29, 2000). From:

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PDF file and html versions from:

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Geophys. Res. Lett. Vol. 27 , No. 5 , p. 719.  (And media story:  

Pearson, P. & Palmer, M.  (2000). "Atmospheric carbon dioxide concentrations over the past 60 million years", Nature, 406, pp. 695-698.

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Weaver, P., Jansen, L., van Grootveld, G., van Spiegel, E. & Vergragt, P. (2000). Sustainable technology development. Greenleaf Publishing: Sheffield, UK.

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Author:  Philip Sutton
First posted:  3 August 2000
Content modified:  29 March 2001
Layout modified:  12 April  2001
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