Those of you who do not read the Journal
of Geography and Natural Disasters before breakfast each morning missed
something interesting. On 17 March that
journal published a paper by M. J. Kelly of Cambridge University on the subject
of “Trends in Extreme Weather Events since 1900- An Enduring Conundrum for Wise
Policy Advice”. Now, we know that human
activities have added a lot of carbon dioxide to the atmosphere since 1900, and
we know that CO2 has a net warming effect on the planet. Numerous press reports have claimed that global
warming must cause an increase in the frequency and severity of extreme weather
events. Interestingly, the
Intergovernmental Panel on Climate Change (usually familiarly referred to as
the IPCC), which has consistently warned about anthropogenic global warming
(AGW), has never endorsed this position.
Global warming, according to both model calculations
and observations, causes the most warming at higher latitudes and the least
warming near the equator. In the
language of meteorology, the meridional
temperature gradient (the temperature contrast between equator and poles)
is decreased. But global weather is
driven primarily by that gradient: when the meridional temperature gradient is
large, polar air is colder relative to equatorial air, so the pole-to-equator
density contrast of Earth-surface air is larger, exerting larger forces to drive
dense polar air toward the equator and vice
versa. The cold air sinks and flows
equator-ward, the warm air rises and flows pole-ward, and the Coriolis effect
diverts these flows into giant circulation patterns, including (at the extreme)
cyclones and hurricanes. A larger
temperature contrast between equator and poles causes larger density differences and pumps more energy
into these global-scale motions. More
energy in the same mass of air means higher velocities. In other words, the obvious effect of global
warming is to reduce the temperature contrast and cause lower wind speeds.
And of course, we humans injected vastly less CO2
into the atmosphere in the 50 years from 1900 to 1950 than we did in the
following 50 years: therefore AGW must have been much stronger in more recent
history.
But so much for how things “ought” to work: Dr.
Kelly has (gasp!) actually looked at the data on weather extremes to address
this issue. He found that “the weather
in the first half of the 20th century was, if anything, more extreme
than in the second half”. In other
words, the actual quantitative data on weather extremes confirms the
common-sense understanding of a decreased meridional temperature gradient and
agrees with the consensus of the IPCC, but flatly contradicts the glib
prophecies of impending doom of the fear-mongers. These prophecies, though quantitatively
unfounded, have the PR virtue of being frighteningly draconic and easily
understood by politicians and policy makers who think and argue qualitatively. But who gets more attention, the person who says "Tomorrow will be a little better than today", or the one who shouts "Disaster coming!"?
Dr. Kelly concludes, “The lack of
public, political and policymaker appreciation of the disconnect between
empirical data and theoretical constructs is profoundly worrying, especially in
terms of policy advice being given.”
You don’t have to take my word for
this. The original technical publication
is available online:
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