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1 It’s not unusually warm
A
physical chill settled on the 14th century at its very start….The Baltic Sea
froze over twice, in 1303 and 1306-07; years followed of unseasonable cold,
storms and rains, and a rise in the level of the Caspian Sea. Contemporaries could not know it was the
onset of what has since been recognized as the Little Ice Age, caused by an
advance of polar and alpine glaciers and lasting until about 1700. Nor were they yet aware that, owing to the climatic
change, communication with Greenland was gradually being lost, that the Norse
settlements there were being extinguished, that cultivation of grain was
disappearing from Iceland and being severely reduced in Scandinavia. But they could feel the colder weather, and
mark with fear its result: a shorter growing season.
- Barbara Tuchman, A
Distant Mirror: The Calamitous 14th Century[1]
We
have to abolish the medieval warm period.
- An unnamed senior researcher, to climatologist David
Deming, 1995[2]
The
current warm cycle peaked in 1998, when the average global temperature (to the
extent that such a measure has any meaning on a planet that routinely
experiences temperature variations of more than 100 degrees) was higher than at
any point in the previous 30 years. The
world, however, was colder in the 1960s and 1970s. It was warmer in the 1930s. It was colder from the High Middle Ages to
the Enlightenment, especially during the Maunder Minimum, a prolonged period of
extremely low solar activity that lasted from 1645 to 1715, and that coincided
with the beginning of the Little Ice Age (ca. 1650-1850). It was warmer in the early Middle Ages,
during the period known as the Medieval Climate Optimum or Medieval Warm Period
(MWP, ca. 1000-1300). It was colder
during the Dark Ages, when the Roman Empire fell. It was warmer during the Roman Warm Period,
when the Republic flourished. It was
colder during the Younger Dryas Cooling, some 13,000 years ago, and also during
the last ice age, which preceded that. It
was colder – much colder – during
each of the glaciations (“ice ages”) that occurred during the past half-million
years. And it was warmer – much warmer – during each of the
interglacial periods that separated them.
Cold and warm periods have alternated throughout the Earth’s
history.
Climate is
cyclical.
The
origins of the cyclical nature of global temperatures remain open to debate,
and many different mechanisms have been postulated, ranging from the Earth’s
axial tilt and its periodic magnetic field reversals, to solar activity (or
inactivity); the position of the Solar System relative the spiral arms of the
Milky Way galaxy; its position above or below the galactic plane; and the
influence, via cosmic radiation, of nearby supernovae or other stellar
phenomena. What is not subject to
dispute, however, is the possibility that human activity may be responsible for
the cyclical nature of climate. Mankind
cannot be responsible for historic and archaeological temperature variations,
because Earth’s temperature has been going up and down throughout its four
billion-year existence, whereas humanity as a species is only two million years
old, and human industrial activity on a measurable scale has been occurring for
only slightly more than a century.
The most
recent example of definitively warmer temperatures was the medieval warm period
(MWP), which began around 1000 A.D., and which lasted – as Tuchman notes in the
above-mentioned quote – until about the 14th Century, when it began
to give way to the Little Ice Age.
The
existence of the MWP has been well-known for centuries,[4]
was not (as AGW theorists tend to claim) restricted solely to Europe,[5]
and featured prominently in the 1990 iteration of the IPCC’s report on climate
(see figure 1).
The IPCC’s
own 1990 temperature chart not only clearly shows the medieval warm period, but
also that it was significantly warmer than current temperatures. Previous warm periods had in fact been warmer
still. Looking back a little further
provides additional useful context.
Loehle and McCulloch, for example, offer a picture of the temperature
patterns over a slightly longer time-frame.
Figures 1
and 2 both clearly show two important facts: first, that the MWP was
significantly warmer than the current average global temperature; and second,
that temperatures during the present era reflect recovery from the low
temperatures associated with the Little Ice Age. It is revealing that the proponents of the AGW
thesis only show the period from the early 19th century onwards,
when temperatures were beginning to increase after the Little Ice Age (LIA). Showing temperature figures from earlier eras
would seriously undermine their contention that current temperatures are
historically unprecedented. They aren’t.
Looking
back further, over a time-frame of 12,000 years, shows an even more significant
disparity, demonstrating the relative difference in temperatures between the
sort of ice ages that have characterized the Holocene era, and the more
congenial temperatures associated with inter-glacial periods (such as that
which humanity has enjoyed for the whole of recorded history).
Clearly
there is nothing particularly special about the current average global
temperature. Climate has been both
significantly warmer in the recent past, and significantly colder (especially
during glaciations). Moreover, the fact
that the world has, for the past 300 years, been recovering from a low point in
the cycle – the Little Ice Age – means that, ceteris paribus, one would expect
temperatures to have increased throughout that period, without having to invoke
any special anthropogenic driving factor.
It should
also be noted that a warmer climate is, on the whole, preferable to a cooler
one. Humanity emerged as a species
during the Holocene climate optimum. As
the above-cited temperature trends demonstrate, warm periods have been
associated, inter alia, with the
emergence of Neolithic culture after the last glaciation; the flourishing of Minoan
and Greek culture; the expansion and success of the Roman Republic; the era of
Medieval cathedral building (an activity that requires not only religious
fervour, but also significant quantities of excess capital and manpower); and
the Italian Renaissance. The recent
warming coincided with the industrial revolution and the remarkable scientific advance
of the past century. A cold climate, by
contrast, restricts agricultural land, reduces growing seasons, requires more
energy to accomplish the same tasks, and increases excess mortality. Historically speaking, humanity has
flourished economically during periods when temperatures were warmer than they
are today, and suffered when they were colder.
What is
significant, however, in the slight temperature increase that we have seen
since the early 1700s is not that it has happened, but rather the question of
where we find ourselves on the cycle of increases and decreases in average
global temperature. In other words, are
we in the midst of an unprecedented and unstoppable linear rise in global
temperatures, as the proponents of the AGW thesis insist? Or are we, as millennia of cyclical
temperature data suggest, on the cusp of another decline?
This
question is addressed in the next section.
NOTES
[1] Barbara Tuchman, A Distant Mirror: The Calamitous 14th
Century (New York: Ballantine Books, 1978), 24.
[2] Cited in Christopher Monckton,
“Hockey Stick? What Hockey Stick? How Alarmist ‘Scientists’ Falsely Abolished
the Medieval Warm Period”, Science and Public Policy Institute, September 2008,
3 [http://scienceandpublicpolicy.org/monckton/what_hockey_stick.html].
[3] IPCC,
“Executive Summary – Chapter Seven”, First Assessment Report (1990), Figure
7.1. According to the IPCC, “The dotted
line nominally represents conditions near the beginning of the 20th
century.”
[4] Writing in 1960, Johannes Brøndsted,
in his definitive treatment of Viking history, noted that when Greenland was
settled in the 10th Century, “the climate there was approximately
the same as it is at its best today (i.e., milder than in the later Middle
Ages).” Johannes Brøndsted, The Vikings, trans. By Kalle Skov
(London: Penguin Books, 1965), 87.
[5] See, for example, T.W.D. Edwards, S.J. Birks, B.H. Luckman and G.M. MacDonald, “Climatic and
hydrologic variability during the past millennium in the eastern Rocky Mountains and northern Great Plains of western Canada”, Quaternary
Research 70 (2008), 188-197.
[6]
Loehle, C., and J.H. McCulloch, “Correction to: A 2000-year global temperature
reconstruction based on non-tree ring proxies”, Energy and Environment, 19,
2008, 93-100.
[7]
Richard A. Muller and Gordon J. Macdonald, Ice
Ages and Astronomical Causes: Data, Spectral Analysis and Mechanisms
(London: Springer-Praxis, 2000), 3.
