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How Warm Is the Earth Nowadays?
Volume 9, Number 39: 28 September 2006

In a recent attempt to put earth's current temperature in a perspective that supposedly emphasizes its unique warmth, Hansen et al. (2006) focus almost exclusively on a single point (0.3N, 159.4E) of the earth's surface in the Western Equatorial Pacific (WEP), comparing modern sea surface temperatures (SSTs) at that location with paleo-SSTs derived by Medina-Elizade and Lea (2005) from the Mg/Ca ratios of the shells of the surface-dwelling planktonic foraminifer Globigerinoides ruber, which were obtained from an ocean drilling program on the Ontong Java Plateau. In doing so, they conclude that "this critical ocean region, and probably the planet as a whole, is approximately as warm now as at the Holocene maximum and within ~1C of the maximum temperature of the past million years," while in another place they say that "recent warming of the WEP has brought its temperature within <1C of its maximum in the past million years."

Is there any compelling reason to believe what these six illustrious researchers are telling us about the entire planet? In a word, no. And why? Because many other single-point measurements suggest something vastly different.

In their own paper, for example, Hansen et al. present data from the Indian Ocean (2.7N, 78.0E) that indicate, as best we can determine from their graph, that SSTs there were about 0.75C warmer than they are currently some 125,000 years ago during the prior interglacial. Likewise, based on data obtained from the Vostok ice core in Antarctica, another of their graphs suggests that temperatures at that location some 125,000 years ago were about 1.8C warmer than they are now; while data from two sites in the Eastern Equatorial Pacific (2N, 91W and 0.5N, 92W) indicate it was approximately 2.3C and 4.0C warmer, respectively, at about that time compared to the present. In fact, the work of Petit et al. (1999) on the Vostok ice core demonstrates that large periods of all four of the interglacials that preceded the Holocene were, on average, more than 2C warmer than it was during the peak warmth of the current interglacial!

But why bother to go so far back in time to make this point? Of the five SST records that Hansen et al. display, three of them indicate that the mid-Holocene was also warmer than it is today. Indeed, it has been known for many years that this portion of the current interglacial was much warmer than it has been subsequently. To cite just a few examples of pertinent work conducted in the 1970s and 80s - based on temperature reconstructions derived from studies of latitudinal displacements of terrestrial vegetation (Bernabo and Webb, 1977; Wijmstra, 1978; Davis et al., 1980; Ritchie et al., 1983; Overpeck, 1985) and vertical displacements of alpine plants (Kearney and Luckman, 1983) and mountain glaciers (Hope et al., 1976; Porter and Orombelli, 1985) - we note that it was concluded by Webb et al. (1987) and COHMAP Members (1988) that mean annual temperatures in the Midwestern United States were about 2C greater than those of the prior few decades (Bartlein et al., 1984; Webb, 1985), that summer temperatures in Europe were 2C warmer (Huntley and Prentice, 1988) - as they also were in New Guinea (Hope et al., 1976) - and that temperatures in the Alps were as much as 4C warmer (Porter and Orombelli, 1985; Huntley and Prentice, 1988). Likewise, in the Russian Far East temperatures are reported to have been from 2C (Velitchko and Klimanov, 1990) to as much as 4-6C (Korotky et al., 1988) higher than they were in the 1970s and 80s; while the mean annual temperature of the Kuroshio Current between 22 and 35N was 6C warmer (Taira, 1975), and the southern boundary of the Pacific boreal region was positioned 700 to 800 km north of its present location (Lutaenko, 1993).

But why bother to even go back to the mid-Holocene? How about looking at the Medieval Warm Period, centered on approximately AD 1100? That's what we do every single week on our website. In fact, we do it twice, in each issue's Medieval Warm Period Records of the Week feature, where we describe two peer-reviewed scientific journal articles that testify to the global extent of this several-centuries-long period of notable warmth. In addition, whenever it is possible to make a quantitative or qualitative comparison between the peak temperature of the Medieval Warm Period (MWP) and the peak temperature of the Current Warm Period (CWP), we add those results to either the quantitative or qualitative frequency distributions we have posted there; and a quick perusal of these ever-growing data bases indicates that the peak warmth of the MWP appears to have been significantly greater than the peak warmth that has been exhibited to date by the CWP.

In conclusion, earth's mean near-surface air temperature is nowhere near the peak level of what it was a million or so years ago. Neither is it as high as it was during the mid-Holocene, which was itself much cooler than all four of the interglacials that preceded it. In fact, it's not even as warm now as it was a mere 900 years ago, when the atmosphere's CO2 concentration was fully 100 ppm less than it is today, which sure doesn't say much for the warming power of this supposedly oh-so-powerful greenhouse gas, nor for the unfounded storyline being promoted by Hansen et al., nor for Hansen himself, who one would think should be well acquainted with these facts.

Sherwood, Keith and Craig Idso

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