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18 research
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eu No. 63 | APRIL 2010
SPECIAL REPORT
CLIM
A
T
E
CLIMATE SCEPTICISM
that the slight climate changes caused by
these fluctuations did affect the carbon cycle
that in its turn influenced past climates.”
The chicken or the egg?
This brings us to another sensitive point
in the debate: the relationship between the
concentration of CO
2
in the atmosphere and
temperature variations. While most climatolo-
gists say that an increased CO
2
concentration
in the atmosphere causes a temperature rise
on Earth, some scientists – and they have
graphs to back them up – stress that over geo-
logical time it is temperature rises that trigger
increased CO
2
concentrations rather than the
reverse. “After a temperature rise caused by
astronomical factors, the oceans heat up and
are less able to absorb atmospheric CO
2
. It is
a law of chemistry: CO
2
dissolves better in cold
water than in warm water. So a greater propor-
tion of CO
2
will remain in the atmosphere.”
So temperature does indeed influence the CO
2
concentration. “Sceptics are right in saying that
in the time scales of the past CO
2
concentrations
followed temperature rises. But once there is a
certain build up, the CO
2
reinforces the natural
greenhouse effect and boosts the warming effect.
Increasing the thickness of the CO
2
layer in the
atmosphere is like putting another blanket on
your bed, it makes you even hotter!”
Tipping the balance
Thus, on closer inspection, relations
between astronomical factors, temperature and
atmospheric CO
2
concentration as highlighted
by the climate sceptics on one hand and by
the ‘climate convinced’ on the other do not
seem so diametrically opposed. The key ques-
tion is therefore what impact the greenhouse
gases emitted by man have on the complex ter-
restrial systems. Here too opinions are divided,
some believing the impact insignificant and
others very significant indeed.
“The CO
2
concentration in the atmosphere
is negligible compared with that of water
vapour, which is the principal greenhouse gas,
and natural CO
2
emissions are much greater
than those of human activities,” is the regular
argument of the sceptics. The greenhouse
effect is most certainly a natural phenomenon
that makes life possible on Earth. Without it,
the average temperature on the earth’s surface
would be -18°C rather than +15°C. “Water
vapour is indeed the principal greenhouse gas.
But the problem is not the greenhouse effect
as such but rather its intensification that is well
documented and that has been measured by
satellite readings over the past 40 years. It is
this intensification that is unquestionably due
to human activity. Analyses of the isotopic
composition of atmospheric CO
2
prove that the
cause of the increase in CO
2
in the atmosphere
is the burning of fossil fuels.”
It is nevertheless true that natural CO
2
emis-
sions are much greater than those originating
in human activities. “During a presentation
on the carbon cycle to the oil federation in
Belgium, in 1997, one climatologist mentioned
that flows of carbon of natural origin amount
to around 200 billion tonnes a year, compared
with 8 billion tonnes of human origin. He there-
fore regarded it as ridiculous to attack this 4 %
represented by anthropic emissions.” But it is
all a question of balance. “What he did not say
is that natural systems recycle their emissions,
in particular through photosynthesis.” These
systems therefore absorb as much carbon
dioxide as they emit. “It is a delicate balance
and if you add anthropic CO
2
on one side, then
that balance is tipped uncontrollably”. What
is more, we are now witnessing mass deforest-
ation that, by reducing the absorption capacity,
is further throwing the whole system off balance.
Slamming the door on the IPCC
The climate models (
2
) on which the IPCC
bases its forecasts are also a subject of debate.
Are they reliable? Most sceptics consider
that we have insufficient knowledge of the
parameters that influence the earth’s climate
to draw any conclusions. “There is never
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