In recent months, we have heard a lot about 350 ppm. Many NGOs have
cottoned on to this figure, probably with no idea of the implications,
in order to try and influence the deliberations of the conference of the
parties which will be held in Copenhagen in December 2009. The simple
answer is that this is a utopian figure which, in itself, is relatively
meaningless. Let me try to explain what it really does mean.
Before I start, let me explain what ppm means. It is a convenient means
of expression of the concentration of a fluid in another fluid, in this
case carbon dioxide in air. It is
not strictly speaking a very scientific unit; scientists much prefer
something like milligrams per cubic metre. Be that as it may, the ppm is
much used and is an abbreviation for parts per million. What is
unspecified is whether the parts are mass or volume. Loosely speaking,
in this context, we assume that it is volumetric. Also, trying to keep
it within the context, if we say that we wish to have a concentration of
carbon dioxide of 350 ppm, we can imagine, for example, a cube of air
with sides of 1 m. This contains 1000 litres or 1,000,000 ml. Our 350
ppm is therefore equivalent to 350 ml in a volume of 1000 l. To
visualise this, 350 ml is about the size of a small can of beer.
Before the industrial revolution, the level of carbon dioxide in the
atmosphere was about 280 ppm, ± 5 ppm and was at about that level for the
thousands of years that man has inhabited this planet. To find significantly
different values, one would have to go back hundreds of thousands of years
or more. This implies that there was a natural equilibrium whereby carbon
dioxide emissions from, say, living organisms, forest fires and the
decomposition of methane was equal to the carbon dioxide absorbed by the
leaves in photosynthesis and by the oceans. Humans have upset this balance by
removing carbon which was naturally sequestered millions of years ago in the form of coal, oil and
natural gas and burning them as well as removing a considerable amount of
vegetable matter by deforestation. This additional loading of carbon dioxide
amounts to over 25 billion tonnes per year, in recent years. There is no way
that the natural sinks of photosynthesis and absorption by the oceans can
cope with this additional loading. In consequence, the level of carbon
dioxide in the atmosphere has been steadily increasing (see the blue line in
the following graph). At the beginning of
the industrial revolution this increase was not severe but as human greed
for more more energy has increased, so has the loading in the atmosphere.
Where it started at about 280 ppm, today it is nearly 390 ppm. There is no
doubt that this increase is entirely due to human activities, even though
some debate whether the 40% increase is the cause of climate change.
We owe the figure of 350 ppm to James Hansen, a climatologist working for
NASA. About two years ago, he considered that this figure was the maximum
global carbon dioxide level that the planet could support without dire
climatic consequences. I'm not sure why he chose this figure and not 300 or
400 ppm. Previous thinking had been around 450 ppm as being "safe". Whether
he is right or wrong does not really matter. Some time later, Dr Rajendra
Pachauri, representing the IPCC's Nobel prize, endorsed the figure of 350
ppm on a private and unofficial basis, without any engagement of the IPCC.
This seemed to put the figure on a more credible level and a number of
organisations, including well-known NGOs, have adopted it as their goal.
Unfortunately, these organisations have not thought the problem through.
Let's apply our imagination to a totally impossible hypothesis. A fairy
waves her magic wand over this planet and we stop extracting fossil fuels
today. The existing carbon dioxide levels (blue line above) are not going to suddenly drop; in fact
they will continue to rise for a number of years (red line) because of the destruction
we have occasioned to the planet, reducing its ability to absorb the gas,
because other greenhouse gases will continue to rise such as methane from
rice paddies and animal farms, because it will take many years to completely
convert the stock of fossil fuel and its derivatives off the face of the
earth and so on. Worse, carbon dioxide takes a long time to decompose in the
atmosphere and to be absorbed in the oceans. It is probable that the rise,
in this hypothetical situation, would continue slowly to increase to somewhere
between 2050 and 2100, with a peak of between 400 and 450 ppm. Only then
will it start to drop, perhaps to reach current levels by about 2200 and,
who knows?, maybe Hansen's magic figure of 350 ppm (green dotted line above) by 2300.
This figure of 350 ppm therefore appears to be utopian and there is no way
that the Conference of Parties in Copenhagen will be seriously able to
introduce this figure, however desirable it may appear, into a successor of
the Kyoto Protocol.
Is there any hope that the Conference will be able to achieve a global
reduction figure? I don't know! I hope so. As a pragmatist, the
best we can hope for is probably no more than a reduction back to 1990
levels by 2020 or 2025. Even this will be extremely difficult, particularly
for countries like India and China. I am more optimistic that the USA may be
able to comply.
If such an agreement were promulgated, how could it be implemented? There
are certainly no easy answers. The magic formula must be a combination of a
hundred different ways of reducing carbon emissions and surely these must
all be implemented together. Some of the main ones which may be implemented
with existing technology are:
- Campaigns for energy conservation
- Better design of energy-consuming equipment
- Cars with lower consumption, notably hybrids
- Maximum use of variable renewables (wind, solar, tide etc)
- Implement widespread waste-to-energy technology
- Improve recycling, wherever feasible
- Introduce new regulations on insulation of buildings, worldwide
- Improve public transport and make it attractive
- More nuclear power stations, including fast breeder reactors etc
Most of these points have been discussed in more detail in other
essays on this web site and I invite you to work through the menu on the
left.