Global warming, models and language - Climate Change: The Facts - page 38

frightening the public. However, when the public is told that every turn of the weather,
whether unusual cold, warmth, snow, drought, etc., is proof of global warming, and when
even the term global warming is changed to climate change, the public soon moves the
issue into the realm of parody with only the chattering classes continuing to pretend belief
in the seriousness of the issue. The writers of insurance policies also find it profitable to
take the claims seriously.
Milankovich vs naïve climate picture
Wehavelongknownthattheearthhasundergoneiceageswhenmassiveicesheetscovered
much of North America and Scandinavia. However, only with the analysis of ice cores
from Antarctica have we had a reasonably detailed history of ice volume, temperature,
and CO 2 . Al Gore's An Inconvenient Truth uses such a record to suggest that CO 2 drives
climate since the record of CO 2 tracks the temperature record. The CO 2 record shows
variations between 180 ppmv and 280 ppmv. The radiative forcing of the high value
relative to the low value is about 2 Wm -2 which is remarkably small.
Moreover, there is substantial evidence that temperature changes preceded CO 2
changes. During World War I, the Serbian astronomer Milutin Milankovitch argued that
orbital changes associated with obliquity cycles, the precession of the equinoxes, and
variations in orbital eccentricity should have a profound effect on glaciation. His thinking
was eminently reasonable. As is well known, the major factor in long term glacial growth
and retreat is summer insolation (the amount of incoming solar radiation). This determines
whethersnowthataccumulatesinwinterwillsurvivethesummer.Ifitdoes,thensnowwill
accumulate forming glaciers.
Milankovitch argued that the relevant quantity for forcing glacial cycles is the
insolation in summer over the Arctic. The orbital variation of this quantity is about 100
Wm -2 , which is huge, compared to the contribution due to CO 2 . Moreover, as the 2002
paper by Sverker Edvardsson et al. and the 2006 paper by Roe have shown, the correlation
of the Milankovitch parameter with the time rate of change of ice volume is about as good
as any correlation in geophysics (earlier claims of poor correlation resulted from using ice
volume rather than its time rate of change). 16 Also, the heat flux is consistent with what
is needed to produce the phase changes involved in glaciations and deglaciations. On the
other hand, the orbital changes result in almost no change whatever in the annually and
globallyaveragedinsolation.Itisthussuggestedthattheminiscule radiative forcingdueto
CO 2 is essential and that the sensitivity is great. What relevance this has to the glaciations
cycles is hard to see.
Thetemperaturechangesassociatedwiththeglaciationscyclesaresufficienttoaccount
for the changes in CO 2 and the small imbalances are easily accommodated by slight