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
We have to abolish the medieval warm period.
- An unnamed senior researcher, to climatologist David Deming, 1995
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, was not (as AGW theorists tend to claim) restricted solely to Europe, 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.
 Barbara Tuchman, A Distant Mirror: The Calamitous 14th Century (New York: Ballantine Books, 1978), 24.
 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].
 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.”
 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.
 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.
 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.
 Richard A. Muller and Gordon J. Macdonald, Ice Ages and Astronomical Causes: Data, Spectral Analysis and Mechanisms (London: Springer-Praxis, 2000), 3.