Geoscience Reference
In-Depth Information
varied between about 500 and 2000 ppm. In effect, since about 450 million years ago plant
photosynthesis has removed CO
2
from the atmosphere, after which normal sedimentary
burial processes led to the conversion of original vegetation to coal and thus the storage
of former CO
2
underground. Utilising coal as an energy resource simply returns the CO
2
to the atmosphere from whence it came in the first place, yielding the twin benefits
of generation of cheap electricity and the greening of the planet. Why radical
environmentalistsviewthisasaproblemhasneverbeenexplainedadequately,andremains
mysterious to this day. For at 280 ppm (pre-industrial), 400 ppm (today), 560 ppm (2 x
pre-industrial) oreven 1120ppm (4xpre-industrial), planet Earth'satmosphere would still
remain in a CO
2
-starved state.
Carbon dioxide is an essential trace-gas for plant photosynthesis, and therefore vital
for biodiversity and the sustenance of most planetary food chains. Adding carbon dioxide
to the atmosphere is beneficial for the growth of many plants, especially cereals, and by
comparison with the last 550 million years of geological history, Earth currently exists in a
state of carbon dioxide starvation.
6
Context 4—efficacy of warming caused by extra carbon dioxide
Carbon dioxide is a potent greenhouse gas for intercepting space-bound (and hence
cooling)radiationemittedfromEarth'ssurfaceatwavelengthsaround14.8µand9µwithin
the electromagnetic spectrum.
Initially, at low atmospheric concentrations, the gas therefore has a strong greenhouse
effect as it blocks outgoing radiation at these wavelengths. However, the narrowness of the
spectral intervals across which CO
2
intercepts radiation results in a rapid saturation of its
effect,suchthateverydoublingintheconcentrationofCO
2
enhancesthegreenhouseeffect
by a constant amount. This is reflected as the negative logarithmic relationship that exists
between extra CO
2
and the warming that it causes.
Because of this logarithmic relationship, the amount of warming caused by increasing
quanta of CO
2
depends upon the level of CO
2
already in the atmosphere, and diminishes
steadily in a 'less-temperature-bang-for-every-incremental-carbon-dioxide-buck' pattern.
Given the pre-industrial starting point of 280 ppm of atmospheric CO
2
, only minor
additionalwarmingwilloccurinresponsetothemuch-feareddoublingofCO
2
to560ppm.
While scientists generally agree that this
prima facie
warming will cumulate to about
1°Cforadoubling,IPCCscientistsallegethatthepositivefeedbackeffectfrommorewater
vapour,itselfgeneratedbytheinitialCO
2
-forcedwarming,willresultinatotalwarmingof
about 3-6°C. However, this speculation conflicts with other empirical data and is therefore
controversial.
