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

• 500 ppmv if emissions continued at 1994 levels until the end of the 21^st century (Intergovernmental Panel on Climate Change, 1996), or
   
• up to around 700 ppmv, by 2100, if the trend growth in emissions follows a "business as usual-including market-led efficiency improvements" trajectory (Intergovernmental Panel on Climate Change, 1995).

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.

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.

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

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).

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:

• bring down world industrial and agricultural CO₂ emissions to zero (net) over the next 60 years, and

• pull CO₂ out of the atmosphere on a net basis for the next 80 years by creating carbon sinks - for example - through revegetation projects to recreate habitat and plantations and changes in agricultural practice to sequester carbon (organic material) in the soil.

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

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

• the CO₂ levels prevailing in the 25 years since 1975 have coincided with the warmest 23 years since record-keeping began in 1866  and with a major decline in most parts of the world of ice sheets, icecaps, glaciers and long duration snow mass.  This change will have significant impacts on ecosystems and human society's dependent on ice-snow environments and on yearly snow melt (Brown, 2000). 

• a level of atmospheric CO₂ of about 360 ppmv (the present level) maintained for the next 50-70 years years is likely to cause the death of virtually all the world’s coral reefs (Hoeg-Guldberg, 1999)

• with unmitigated emissions, substantial dieback of tropical forests and tropical grasslands is predicted to occur by the 2080s, especially in parts of northern South America and central southern Africa. Under emissions scenarios leading to stabilisation of CO₂ at 750 ppm, the dieback of tropical forests is delayed by about 100 years^[6]. (White & Cannell,1999)  The massive tropical forest fires over the last few years (eg. Brazil and Indonesia), which are coincident with current CO2 levels, may be the early indicators of this change.

• at an atmospheric CO₂ level of between two and three times the natural level ie. between 550 and 800 parts per million (and above) the thermohaline circulation that keeps the deep oceans oxygenated could well cease altogether due to greatly reduced formation of sea ice at the poles^[7]. A de-oxygenated ocean below 1 to 1.5 km would result. (A doubling of atmospheric CO₂ could be reached by about 2033 and the shut-off of the deep ocean circulation could have been completed within 150 years. (Hirst, 1999; Strong, 1999; 2000)

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 21^st 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.

Conclusion

• greenhouse gas emissions need to be brought down to zero and a large amount of previously emitted CO₂ needs to be stripped out of the atmosphere

• the economic restructuring that is needed to make this possible needs to be virtually completed within 25 years (by 2025).

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:

• atmospheric CO2 levels be stabilised under 550 ppmv, and that

• CO₂ emissions be cut by some 60% by 2050 - which would necessarily require large reductions in fossil fuel consumption.

Where to from here?

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 www.natcap.org, 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)

http://www.natcap.org/sitepages/pid20.asp

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.

Footnotes

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.) peter.whetton@dar.csiro.au)
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).

References

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Flannery, T. (1994). The Future Eaters: An ecological history of the Australian lands and people. Reed: Port Melbourne, Victoria.

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