Historical Temperature Trends In Antarctica

By Paul Homewood

 

http://scienceandpublicpolicy.org/images/stories/papers/originals/antarctica_trends.pdf

 

 

SPPI have just published “Historical Temperature Trends In Antarctica”, which gives an overview of recent studies of temperature trends from the ice age to the present day. The paper is 14 pages long, but I will try to sum up the main points here.

The first section summarises the glacial periods, really making the, now well established, point that temperature changes preceded CO2 changes, and did not follow. As I say, this is now well established, so I will move on to the next section.

 

The Holocene

The paper identifies several studies which provide evidence that Antarctic temperatures were higher than now in both the Roman Warm Period and the Medieval Warm Period. There is also substantial evidence of the Little Ice Age there.

For instance:

 

Focusing on a more recent time interval, Yoon et al. (2002) wrote that "the maritime record on the Antarctic Peninsula shelf suggests close chronological correlation with Holocene glacial events in the Northern Hemisphere, indicating the possibility of coherent climate variability in the Holocene." And in much the same vein, Khim et al. (2002) stated that "two of the most significant climatic events during the late Holocene are the Little Ice Age (LIA) and Medieval Warm Period (MWP), both of which occurred globally (Lamb, 1965; Grove, 1988)," while further noting that "evidence of the LIA has been found in several studies of Antarctic marine sediments (Leventer and Dunbar, 1988; Leventer et al., 1996; Domack et al., 2000)."

 

To this list of scientific journal articles documenting the existence of the LIA in Antarctica can Khim et al.’s own paper be added, for it also demonstrates the presence of the MWP in Antarctica, as well as earlier cold and warm periods of similar intensity and duration. Hence, it is becoming ever more difficult for climate alarmists to continue to claim that these several-hundred-year cold and warm periods were confined to lands bordering the North Atlantic Ocean. They clearly were global; and they clearly demonstrate the reality of the likely solar-induced millennial-scale climatic oscillation that is manifest in the post-1850 warming of the world that climate alarmists misconstrue as having been caused by the concomitant rise in the air’s CO2 content.

 

To further drive home this point, Stenni et al. (2002) examined a number of paleoclimatic indicators in two firn cores that were retrieved from the Talos Dome area of East Antarctica in 1996, with accurate dating being provided by non-sea-salt sulfate spikes associated with well-documented volcanic eruptions and with tritium activity associated with known atmospheric thermonuclear bomb tests. The results of their work were compared with those based on other East Antarctic ice core records obtained from Dome C EPICA, Taylor Dome and the South Pole; and, in the words of the seven scientists, the several records suggested cooler climate conditions between the middle of [the] 16th and the beginning of [the] 19th centuries, which might be related to the Little Ice Age (LIA) cold period." And after discussing still other findings, they concluded that "more and more evidence coming from ice core records, glacier extension and other proxy records are leading to the idea that the Antarctic continent or at least East Antarctica also experienced the LIA cool episode," out of which the continent (like the rest of the world) began to emerge into what is now known as the Current Warm Period (CWP).

 

One year later, Cremer et al. (2003) reconstructed a history of environmental change in the southern Windmill Islands, East Antarctica, based upon diatom assemblages obtained from two long and well-dated sediment cores removed from two marine bays, comparing their findings with those of studies of several other parts of Antarctica. This work revealed, in the words of the four researchers, that "the diatom assemblage in the upper sediments of both cores indicates Neoglacial cooling from ~1000 cal yr BP," and that this latest thousand-year period "is generally marked by distinct cooling leading to glacial re-advances, more extensive sea-ice, lower precipitation, and lower bioproductivity." In addition, they report that "this climatic deterioration is visible in nearly all available Antarctic terrestrial and marine records (e.g. Ingolfsson et al., 1998; Jones et al., 2000; Roberts et al., 2000, and references therein)."

[Interesting that they identify more extensive sea ice with a colder climate]

 

Shortly thereafter, Roberts et al. (2004) conducted a fossil diatom analysis of an 82-cm sediment core that covered the approximate time period 2000-1700  BP and was removed from the deepest part of Beall Lake in the northern Windmill Islands in one of the more significant ice-free oases on the East Antarctic coastline, samples of which were radiocarbon dated and corrected for the Antarctic reservoir effect. And based on the species of diatoms found in this sample, they inferred the existence of a multi-centennial period of warmth that was characterized by summer temperatures they describe as being "much higher than present summer temperatures." Supporting this inference, they also noted that observations made at both Casey and Law Dome indicated that "during the late Holocene, a warm period existed with precipitation and summer temperatures higher than at present (Goodwin, 1993)." And to make this point perfectly clear, they concluded their report by stating that "the diatom-inferred Holocene palaeosalinity record from Beall Lake indicates that the late Holocene warm period was much warmer than at present." And the dates they give for this period suggest that it was part of the well-known Roman Warm Period.

 

Two years later, Hall et al. (2006) collected skin and hair – and even some whole-body mummified remains – from Holocene raised-beach excavations at various locations along Antarctica’s Victoria Land Coast, which they identified by both visual inspection and DNA analysis as coming from southern elephant seals , and which they analyzed for age by means of radiocarbon dating. Data from fourteen different locations within Hall et al.’s study region – which they describe as being "well south" of the seals’ current "core sub-Antarctic breeding and molting grounds" – indicate that the period of time they denominate the Seal Optimum began about 600 BC and ended about AD1400, "broadly contemporaneous with the onset of Little Ice Age climatic conditions in the Northern Hemisphere and with glacier advance near [Victoria Land’s] Terra Nova Bay. The US, British and Italian researchers say their findings indicate "warmer-than-present climate conditions" at the times and locations of the identified presence of the southern elephant seal.

 

The Past Few Decades

Doran et al. (2002) examined temperature trends in the McMurdo Dry Valleys of Antarctica over the period 1986 to 2000, reporting a phenomenal cooling rate of approximately 0.7°C per decade. This dramatic rate of cooling, as they describe it, "reflects longer term continental Antarctic cooling between 1966 and 2000." In addition, the 14-year temperature decline in the dry valleys occurred in the summer and autumn, just as most of the 35-year cooling over the continent as a whole (which did not include any data from the dry valleys) also occurred in the summer and autumn.

 

In another study, Comiso (2000) assembled and analyzed Antarctic temperature data obtained from 21 surface stations and from infrared satellites operating since 1979, finding that for all of Antarctica, temperatures had declined by 0.08°C and 0.42°C per decade, respectively. And in a contemporary study, Thompson and Solomon (2002) also reported a cooling trend for the interior of Antarctica.

 

What about the Antarctic Peninsula , which has warmed significantly in the last 50 years? There is plenty of evidence that it was as warm in the past, for instance.

 

According to Vaughan et al. (2001), "rapid regional warming" has led to the loss of seven ice shelves in this region during the past 50 years. However, they note that sediment cores from 6000 to 1900 years ago suggest that the Prince Gustav Channel Ice Shelf – which collapsed in this region in 1995 – "was absent and climate was as warm as it has been recently.

 

Much more recently, Mulvaney et al. (2012) drilled an ice core to the bed of the ice cap on James Ross Island, which lies just off the northeastern tip of the Antarctic Peninsula… This work revealed that "the Antarctic Peninsula experienced an early Holocene warm period followed by stable temperatures, from about 9200 to 2500 years ago, that were similar to modern-day levels." They also found that "the high rate of warming over the past century is unusual (but not unprecedented) in the context of natural climate variability over the past two millennia.

 

And there is ample evidence that the warming of the Peninsula has been due to natural causes.

 

Thompson and Solomon (2002) suggest that much of the warming can be explained by "a systematic bias toward the high-index polarity of the SAM," or Southern Hemispheric Annular Mode, such that the ring of westerly winds encircling Antarctica has recently been spending more time in its strong-wind phase. This was also the conclusion of Kwok and Comiso (2002).

Turner et al (2005) also point out that the region of marked warming is “quite limited and is restricted to an arc from the southwestern part of the peninsula, through Faraday to a little beyond the tip of the peninsula."

 

Back to Antarctica as a whole, Schneider et al (2006) offers a slightly longer perspective.

 

One year later, Schneider et al. (2006) utilized 200 years of sub-annually-resolved ð18O and ðD records from precisely-dated ice cores obtained from Law Dome, Siple Station, Dronning Maud Land and two West Antarctic sites of the United States component of the International Trans-Antarctic Scientific Expedition to create a 200-year-long Antarctic temperature reconstruction representing the main part of the continent. The results of this significant undertaking, following application of a multi-decadal low-pass filter to the yearly data, are presented in the figure below, along with the similarly-treated data of the Southern Hemisphere instrumental temperature record, where the zero line represents the 1961-1990 climatological means of the two records.

 

This temperature history not only shows recent cooling, it also indicates that temperatures are now lower than the early 19thC.

There are too many other studies to quote, which all come to similar conclusions, but they can be well summed up by this conclusion from Monaghan & Bromwich (2008):

 

“Overall there have not been statistically significant Antarctic near-surface temperature trends since the International Geophysical Year" of 1957-58”

 

Conclusion

In conclusion, and in light of the many findings of the diverse studies cited above, it is clear that the temperature history of Antarctica provides no evidence for the CO2-induced global warming hypothesis. In fact, it argues strongly against it.