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Stabilising Climate

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Clive Best

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2016년 12월 12일 오전 4:14


In order to stop global warming all we really have to do is to stabilise CO2 emissions, not reduce them to zero!  One of the 'myths' promoted by IPCC climate scientists is that we have to stop burning any fossil fuels i.e. we must 'keep it in the ground'. This is a total fallacy as I will try to explain in this post.

Carbon dioxide sources and sinks must balance once stability is reached

The origin of this belief that we must stop burning all fossil fuels by ~2050 can be traced back to Figure 10 which appeared in the AR5 'Summary for Policy Makers'. Here it is.

Figure 10 from SPM AR5

Figure 10 was intended to send a simple message to the world's political leaders. Namely that there is a finite total amount of fossil fuel that mankind can safely burn, and that we have already burned half of it.  Therefore unless the major industrialised countries stop burning fossil fuels altogether by 2050, the world will warm far above 2C (red curve) causing a global disaster. This message worked, but there is so much wrong about the hidden assumptions and even subterfuge used to produce Figure 10 that I wrote a post about it at the time.

The principal assumptions hidden from view under Fig 10. are:

  1. Carbon sinks are saturating (they are not)
  2. ECS (Equilibrium Climate Sensitivity)  is 3.5C (Uncertain – and could be as low as 1.5C)
  3. Replacement of logarithmic forcing of CO2  with a linear forcing.

As a direct consequence of IPCC successful lobbying based around Figure 10, the Paris treaty now proudly "sets the world on an irreversible trajectory on which all investment, all regulation and all industrial strategy must start to align with a zero carbon global economy". Does anyone really believe that this is even feasible, let alone realistic? It simply is not going to happen because well before then their citizens will revolt and kick them out. The best we can hope for in the short term is a stabilisation in the annual global CO2 emissions.

I argue that by simply stabilising emissions, we can halt global warming. Clearly the lower total 'stable' emissions are then the cooler the planet will be, but even if we only managed to stabilise emissions at current values the net warming will still be <2C and CO2 levels will stop rising and stabilise at <410 ppm.

Atmospheric CO2 levels must always reach an equilibrium as the natural carbon sinks will catch up to balance emissions. For the last 40 years about half of man-made emissions have been absorbed mainly into the oceans, but also into soils and biota. The reason why CO2 levels have been continuously increasing since 1970 is that  we have been increasing emissions each year, so the sinks have never been able to catch up. Sinks will quickly balance emissions and CO2 levels will stop rising once emissions stop increasing. This fact is obvious because run-away CO2 levels have never happened in the earth's long history. Such a balancing mechanism has always stabilised atmospheric CO2 over billions of years during intense periods of extreme volcanic activity, ocean spreading and periodic tectonic mountain building. Fossil fuels are an insignificant fraction when compared to  the buried carbon contained in sedimentary rocks.

To see how this works let's assume that the world can stabilise annual emissions at current rates of 34 Gtons CO2/year  indefinitely. We know that CO2 sinks currently absorb half of that figure – 17 Gtons and have been increasing proportional to the increase in partial pressure of CO2 in the atmosphere – currently 400ppm. Stabilising emissions would result in the increasing fractional uptake by carbon sinks of the now fixed emissions. The remaining fraction of annual emissions that would remain in the atmosphere is therefore as follows.

Year 1: 50%  Year 2: 25% Year 3: 12.5% etc. This is simply equal to the infinite sum

So CO2 levels in the atmosphere will  taper off after just ~10 years to reach a new long term value equivalent to adding an additional 34 Gtons of CO2 to the atmosphere. The atmosphere currently contains 3.13 x 10^12 tons of CO2 so the net increase at equilibrium would be only an extra  1%. Therefore for the years following 2016 the resultant CO2 curve looks like this.

There is also a very good chance that we can achieve such a fixed limit, rather than pretend to meet an impossible target of zero emissions. However this  does mean that CO2 levels will remain at 404 ppm indefinitely, which is far higher than a planet without human beings, but still leaves us plenty of time to replace fossil fuels,  with new nuclear energy.

Controlling CO2 levels by stabilising emissions also has one huge advantage. It means that we can  eventually control the level of 'enhanced global warming' so  avoiding another devastating ice age, otherwise due to begin within 5000 years time.



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