Posted on 11/20/2003 6:27:32 PM PST by farmfriend
Same Old Story
By David R. Legates
The conventional wisdom has been that temperatures during the early years of the last millennium (~A.D. 800 to 1300) were relatively warmer -- in what was known as the Medieval Warm Period -- while temperatures decreased during the middle years of the millennium (~A.D. 1400 to 1850) -- during what was known as the Little Ice Age. During the 1900s, temperatures increased as a result of a number of factors, including the demise of the Little Ice Age. Both introductory scientific texts as well as extensive scientific literature confirm these facts.
But in 1999, Dr. Michael Mann of the University of Virginia and his colleagues produced what has now become known as the 'hockey stick' curve -- a representation of the annual temperature for the Northern Hemisphere over the last millennium. This curve, compiled by averaging a number of proxy records (secondary or inferred sources from which assumptions about temperature can be drawn), shows a very slight cooling trend from A.D. 1000 to 1900 with a dramatic warming during the 1900s. This led Dr. Mann, the Intergovernmental Panel on Climate Change (IPCC), and the US National Assessment of Climate Change to assert that the 1990s were the warmest decade of the last millennium with 1998 being the warmest year.
But is the "hockey stick" assumption consistent with the observations? Harvard astrophysicists Dr. Willie Soon and Dr. Sallie Baliunas and their colleagues contend that it isn't. After examining more than 240 individual proxy records analyzed by nearly 1000 researchers, they concluded that taken individually, proxy records offer strong support for the widespread existence of both the Medieval Warm Period and the Little Ice Age and that they do not support the claim that the climate of the 20th Century is unusual when compared to the variability over the last millennium.
So why does Mann's "hockey stick" representation of average Northern Hemisphere temperature fail to retain the fidelity of individual proxy records? Many reasons involve detailed statistical issues, although some are rather obvious and fundamental. For example, Mann contends that the curve represents Northern Hemisphere temperature trends. So why is it that four of the twelve proxy sources used for the pre-A.D. 1400 analysis are from the Southern Hemisphere? Mann also simply affixed thermometer-based estimates for the 1900s to the end of his proxy averages -- a classic apples-versus-oranges comparison -- thereby producing the characteristic 'hockey stick' shape. But the thermometer-based record shows more variability than the proxy records during the 1900s and Mann represents it without the assignment of uncertainty. If the thermometer-based record was not included or if a satellite-based temperature record (where only a small warming trend exists for the late 1900s) were used instead, the claim that the 1990s were the warmest decade becomes unfounded. Even if a reasonable estimate of the error in the thermometer-based record were provided, the claim becomes questionable. Moreover, the range of uncertainty for the pre-A.D. 1400 analysis depends on a single proxy source for western North America; and Mann admits that his entire millennial reconstruction hinges on that single source.
But do proxy records really represent air temperature fluctuations? Most of the analyses on which the "hockey stick" relies are taken from tree-ring cores. Trees, however, respond not only to temperature fluctuations but also to species competition, fire episodes, pest infestations, and droughts. For example, if rainfall is limited, as often is the case in western North America (where the preponderance of data for Mann's pre-A.D. 1400 analysis is located), tree growth is severely restricted, regardless of the temperature conditions. It is impossible under such conditions to discriminate between a cold period and a dry period -- which is why Soon and Baliunas correctly characterized their assessments as "climate anomalies" rather than boldly assert they reflect air temperature fluctuations, as Mann does. Moreover, Dr. Jan Esper of the Swiss Federal Research Institute and colleagues demonstrated that their careful analysis of tree-ring chronologies yields an annual temperature curve for a large portion of the Northern Hemisphere that, unlike the "hockey stick," clearly shows the existence of the Medieval Warm Period and that temperatures during the early years of the millennium were commensurate with those of the 1900s.
These and other more complex issues are fundamental reasons the "hockey stick" is being challenged on scientific grounds by a number of serious scientists. But the IPCC and the US National Assessment of Climate Change continue to demand that policy be based on this flawed and biased research. We must take a closer look at the "science" behind the IPCC and, in this case, ask the question, "How much of the warming of the 20th Century was 'man-induced' and how much of it is 'Mann-induced'?"
David R. Legates is Associate Professor and Director of the Center for Climatic Research at the University of Delaware and Research Fellow at the Independent Institute in Oakland, Calif., publisher of the new report, New Perspectives in Climate Change: What the EPA Isn't Telling Us (www.independent.org).
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Challenges to the revisionist Mann Hockey Stick continue to arrive from various quarters. Yesterday C02 Science Magazine reported on a study of Chinese climate over the same period:
"From the beginning of the Christian era, climate became cooler at a rate of 0.17°C per century," which correlates well with the fact that this is the period of time when the planet slipped out of the Roman Warm Period and entered into the Dark Ages Cold Period, "and around the AD 490s temperature reached about 1°C lower than that of the present (the 1951-80 mean)."
"Then, abruptly, temperature entered a warm epoch from the AD 570s to 1310s with a warming trend of 0.04°C per century; the peak warming was about 0.3-0.6°C higher than present for 30-year periods, but over 0.9°C warmer on a 10-year basis." This finding pretty much speaks for itself. For a considerable amount of time during the Medieval Warm Period, this large chunk of China was warmer than has yet to be experienced in modern times over a similarly-extended time span.
"After the AD 1310s, temperature decreased rapidly at a rate of 0.10°C per century; the mean temperatures of the four cold troughs were 0.6-0.9°C lower than the present, with the coldest value 1.1°C lower." This, of course, was the Little Ice Age, from which the world appears to still be in processes of recovering."
Figures don't lie, but liers sure can figure.
After about five years, the "Hockey Stick" has finally been subjected to some serious scrutiny and serious questions are being asked. Dr. Mann has a lot of 'splaining to do.
Actually its all the fault of the Reagan administration ;O)
IF the Soviet Union hadn't imploded, we would probably not be seeing any "Hocky Stick."
McKitrick, Ross R. "An Economists Perspective on Climate Change and the Kyoto Protocol" pages 5&6
Presentation to the Department of Economics Annual Fall Workshop
The University of Manitoba
November 7, 2003
http://www.uoguelph.ca/~rmckitri/research/econ-persp.pdfIn the early 1990s, the collapse of the Soviet Union and the budget cuts in many OECD economies led to a sudden sharp drop in the number of active weather stations.
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Figure 3 shows the total number of stations in the GHCN[Global Historical Climatology Network] and the raw (arithmetic) average of temperatures for those stations. Notice that at the same time as the number of stations takes a dive (around 1990) the average temperature (red bars) jumps. This is due, at least in part, to the disproportionate loss of stations in remote and rural locations, as opposed to places like airports and urban areas where it gets warmer over time because of the build-up of the urban environment.
This poses a problem for users of the data. Someone has to come up with an algorithm for deciding how much of the change in average temperature post-1990 is due to an actual change in the climate and how much is due to the change in the sample. When we hear over and over about records being set after 1990 in observed global temperatures this might mean the climate has changed, or it means an inadequate adjustment is being used, and there is no formal way to decide between these.
Nevertheless, confident assertions are routinely made about changes in the global temperature on the order of tenths of a degree C per decade. The confidence masks pervasive uncertainty in the underlying concepts and data quality.
Figure 3. Number of stations in GHCN collection (diamonds, right axis); Average temperature of annual sample (bars, left axis in C). Source: see Taken By Storm chapter 4.
Note, above, how well the insturmental global surface temperature series tracked with Tropospheric(Satellite & Balloon) measurements up until the 1990-91 time frame; then diverge while we observe the number of remote surface stations continue to decline.:
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