This perception has been amplified considerably in the public psyche by Al Gore and James Hansen, the former in his testimony of 21 March 2007 before the U.S. Senate's Environment and Public Works Committee, and the latter in his testimony of 26 April 2007 before the Select Committee of Energy Independence and Global Warming of the U.S. House of Representatives. But are these perceptions consistent with real-world observations? In this Summary, we briefly recapitulate what has been learned in this regard by a number of scientists who specialize in this particular field of research.

We begin in China with the work of Zhuo et al. (1998), who reviewed our knowledge of climatic conditions in that country during the Holocene Optimum, or the central portion of the planet's current interglacial epoch. Synthesizing the results of a broad range of studies, they determined that temperatures during this period were 2-6°C warmer than at present. This warmer climate resulted in the retreat of glaciers across the country, some of which disappeared altogether in eastern China, while it also resulted in a retreat of the southern permafrost limit to 100 km north of its current location.

Also working in China, Jin et al. (2007) studied the evolutionary history of permafrost in the central and eastern Qinghai-Tibetan Plateau. Among their many findings, we focus our attention on their descriptions of permafrost and climatic conditions during (1) what they call "the Megathermal period in the middle Holocene (~8500-7000 to ~4000-3000 years BP)," which period is more commonly known as the Holocene Climatic Optimum, and (2) "the warm period in the later Holocene (1000 to 500 years BP)," which is commonly known as the Medieval Warm Period or MWP. This research led them to conclude that during the Holocene Climatic Optimum, areas of permafrost were about 40-50% of those at present, and that mean annual air temperatures were 2-3°C higher. Likewise, they report that during the MWP "the retreating of permafrost resulted in a total permafrost area of ~20-30% less than at present," and that mean annual air temperatures were "1.5-2.0°C warmer than at present."

Across the top of the world in a study conducted in Alaska, Muhs et al. (2001) presented proxy climate data for central Alaska during the previous interglacial and compared their results with those obtained by other researchers for the same region and time period. This analysis revealed that the overall picture for Alaska and the Yukon during the peak warmth of the last interglacial was that of "a region with warmer-than-present summers, an absence of permafrost in the interior, and probably greater precipitation in the interior." How much warmer was it? Based upon the expanded boreal forest ranges in this area, they estimate that summer temperatures were at least 1-2°C warmer than they are presently, and that in some locations summer temperatures may have been as much as 3-5°C higher than they are now.

What are the implications of these findings? In spite of the significantly higher-than-current temperatures and greater-than-current melting of Chinese and Alaskan-Yukon permafrost throughout the Medieval Warm Period, the Holocene Climatic Optimum and the prior interglacial epoch, atmospheric methane concentrations reconstructed from Antarctic ice core data indicate that during the second of these warm intervals, methane concentrations were at an interglacial minimum on the order of 600 ppb or less, while during the MWP, centered on about AD 1000, they ranged between 600 and 700 ppb, which values are to be compared to values close to 1800 ppb today. Hence, it should be abundantly clear that a warming and melting of permafrost -- even far in excess of what has occurred in our day -- could not produce the envisioned catastrophic increases in atmospheric methane concentration about which climate alarmists claim to be so concerned. In fact, recurrent interglacial warmings have not been able to do so over the past 650,000 years that we have been able to track atmospheric methane concentration via Antarctic ice-core data (Loulergue, 2008), even during the prior four interglacials, which experienced maximum temperatures that exceeded those of the Holocene Climatic Optimum by an average in excess of 2°C (Petit et al., 1999). Consequently, whatever further warming of the globe might yet occur will almost certainly not lead to inordinate increases in the air's methane concentration. In fact, they may well result in no increase at all.

In another study that came to essentially the same conclusion, Delisle (2007) employed a uni-dimensional long-term permafrost temperature model that incorporates all relevant thermal processes within the active layer and the permafrost, and the region between the permafrost and the non-frozen ground below -- the transition zone that Shur et al. (2005) showed to be of great importance -- to determine what might occur if surface temperatures were to rise at a rate as high as 0.8°C per decade for a full century. In doing so, the German researcher found that "permafrost will mostly prevail in this century in areas north of 70°N," even for an unbelievable total warming of 8°C, and that "permafrost will survive at depth in most areas between 60° to 70°N."

As a result, Delisle wrote that "based on paleoclimatic data and in consequence of this study, it is suggested that scenarios calling for massive release of methane in the near future from degrading permafrost are questionable." In this statement, the reference to paleoclimatic data pertains, in Delisle's words, to the "limited amount of organic carbon that had been released from permafrost terrain in previous periods of climatic warming such as e.g. the Medieval Warm Period or during the Holocene Climatic Optimum," when "there appear to [have been] no significant methane excursions in ice core records of Antarctica or Greenland during these time periods (see e.g., Chappellaz et al., 1997), which otherwise [our italics] might serve as evidence for a massive release of methane into the atmosphere from degrading permafrost terrains."

In one final study, which reaches further back in time than all of the others, Froese et al. (2008) investigated relict ground ice within the discontinuous permafrost zone of Canada's central Yukon Territory, where they found large vertically foliated ice wedges within a few meters of the surface that were overlain by a volcanic ash layer, the age of which they determined by means of isothermal plateau glass fission-track and diameter-corrected glass fission-track methods. These measurements provided, in their words, "a weighted-mean age of 740,000 ± 60,000 years before present," which they indicate is consistent with "faunal ages associated with this bed and the normal magnetic polarity of the surrounding sediments."

As for the implications of this finding, Froese et al. say it indicates that "permafrost has survived within the discontinuous permafrost zone since at least the early-Middle Pleistocene," noting that "this age range includes several glacial-interglacial cycles ... considered to be longer and warmer than the present interglaication." Most important of all, therefore, they say their finding "highlights the resilience of permafrost to past warmer climate and suggests that permafrost and associated carbon reservoirs that are more than a few meters below the surface may be more stable than previously thought," taking much of the wind out of the sails of those who claim these carbon stores will soon be released to the atmosphere in consequence of what they call the unprecedented warming of the late 20th century and its projected continuation over the remainder of the current century.

Hence, it is clear that another of the climate alarmists' cherished catastrophic scenarios is destined to soon take its well-deserved place atop the ash heap of history.

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