/* Written 3:21 PM Sep 26, 1995 by moore@Hoover.Stanford.EDU in igc:sci.environmen */ Answer to critics of Global Warming paper Many of the criticisms of the paper on Global Warming miss the point and deal with peripheral issues. The thrust of the paper is that since the last ice age the globe or major portions of the globe enjoyed significantly warmer weather for at least two periods -- about 3,000 to 8,000 years ago and during the Medieval period for about two hundred to three hundred years. During these two periods mankind and much of nature flourished. The warming during the first period shows up well in recent ice core data (1, 2). This evidence supports the proposition that it was a worldwide phenomenon. Evidence that the second period was worldwide, perhaps because it was relatively short, is less strong but exists. I present some evidence of it in my paper and will not repeat it here. The latest evidence, however, comes from a volume of CLIMATE CHANGE devoted entirely to the subject of the existence of a Medieval warming period.(3) Malcolm Huges and Henry Diaz summarized the findings and wrote: "Our review indicates that for some areas of the globe (for example, Scandinavia, China, the Sierra Nevada in California, the Canadian Rockies and Tasmania) temperatures, particularly in summer appear to have been higher during some parts of this period than those that were to prevail until the most recent decades of the twentieth century. These warmer regional episodes were not strongly synchronous. Evidence from other regions (for example, the Southeast United States, southern Europe along the Mediterranean, and parts of South American) indicates that the climate during that time was little different to that of later times, or that warming, if it occurred was recorded at a later time than has been assumed." They go on to say: "Taken together, the available evidence does not support a *global* Medieval Warm Period, although more support for such a phenomenon could be drawn from high-elevation records than from low-elevation records." One quarrel with their conclusion is that the evidence indicates that all of northern Europe was warm, not just Scandinavia. For example, grapes and wine were produced much further north than either subsequently or today. Farming took place at higher elevations in the mountains than is currently the practice. Written records from large estates in England and on the Continent indicate better weather. Their summary neglects to mention the Southwest portion of what is now the U.S. Kenneth Petersen in the same volume summarizes his research findings: "The zenith of Anasazi Pueblo Indian occupation in the northern Colorado Plateau region of the southwestern U.S.A. coincides with the Little Climatic Optimum or Medieval Warm Period (A.D. 900-1300) and its demise coincides with the commencement of the Little Ice Age. ... The results show that during the height of the Little Climatic Optimum (A.D. 1000-1100) the region was characterized by a relatively long growing season and by a potential dry farming zone or elevational belt (currently located between 2,000 m and 2,300 m elevation) that was twice as wide as present and could support Anasazi upland dry farming down to at least 1,600 m, an elevation that is quite impossible to dry farm today because of insufficient soil moisture. This expanded dry-farm is attributable to a more vigorous circulation regime characterized by both greater winter and summer precipitation than that of today. Between A.D. 1100 and 1300 the potential dry-farm belt narrowed and finally disappeared with the onset of a period of markedly colder and drier conditions than currently exist." Ricardo Villalba wrote about Southern South America "The first cold interval was from A.D. 900 to 1070, which was followed by a warm period A.D. 1080 to 1250 (approximately coincident with the *Medieval Warm Epoch*). Jean Grove and Roy Switsur writing on "Glacial Geological Evidence for the Medieval Warm Period" summarized their findings: "The results suggest that it was a GLOBAL EVENT occurring between about 900 and 1250 A.D., possibly interrupted by a minor readvance of ice between about 1050 and 1150 A.D." (my capitalization). IMHO the above gives overwhelming support to the proposition that much if not all of the globe was affected. It is probably true that lower latitudes were much less impacted that higher ones. Scandinavia benefited much more than Italy. The benefits from warming do seem to have been more concentrated either in the northern climates or in areas which received more rainfall because the monsoon moved to higher latitudes. Even if the warming were not worldwide the effect of regional warming on people in those areas would be illustrative. As my paper on Global Warming pointed out the warming seems to have started in the Orient and made its way westward. The striking aspect of both the earlier warming and the later one is the rapid increase in population. I know that today we view growth in numbers of people as bad, but until the industrial revolution a simple rule of thumb would be that when a group was doing well their population expanded and when it suffer the numbers would fall. I have a chart in my essay on Global Warming that unfortunately does not come through in the on-line versions. My chart shows that during the warmest period 5000 B.C. to 1000 B.C. the world's population grew 0.050 percent faster annually than would be expected. During the cold period of the Mini Ice Age (1300-1800) it grew 0.034 percent annually slower than other wise would be expected and during the Medieval Warm Period it grew slightly faster than expected (0.001 percent). Although these percent changes look small over a few hundred years they make a big difference. Many historians who have generally ignored the influence of climate have been quite puzzled by the growth in population in Europe during the Medieval period. We also have estimates of life expectancy from England for the Medieval Warm Period of 48 years, compared to 38 years for the Mini Ice Age period and 38 years for the Neolithic. (These numbers can be found in my paper). Rich Puchalsky has called my evidence anecdotal. The above data on population is not anecdotal, nor is the life expectancy figures. I presume that he is referring to my citation of major construction projects around the world. I think almost any historian would agree that the construction of cathedrals in Europe during the "little Climate optimum" was unparalleled. Until the 19th and 20th century there has been so comparable building boom. As economists know, and as most people who follow the financial news know, good times are typically accompanied by significant construction activity. While we have no data on GNP during the High Middle Ages we can draw valid inferences from construction activity. It is noteworthy that the construction halted in the 14th century, when the climate turned colder and the population plunged. It is not anecdotal that per capita real earnings reached its highest level until very recently during the Northern Sung Dynasty (961 A.D. to 1127).(4) Chinese landscape painting also reached a peak. The Chinese climate was also warmest during this period. Coincidence? I think the case is very strong that warmer is better and colder is worse. (1) T. Sowers and M. Bender "Climate Records Covering the Last Deglaciation" SCIENCE 269 (14 July 1995), pp 210-213. (2) L. Thompson, et al, "Late Glacial Stage and Holocene Tropical Ice Core Records from Huascaran Peru" SCIENCE 269 (7 July 1995). (3) CLIMATE CHANGE 26 (March 1994). (4) Kang Chao MAN AND LAND IN CHINESE HISTORY: AN ECONOMIC ANALYSIS, Stanford: Stanford University Press (1986).