April 21, 2008

Little Ice Age in Southern South America?

Recall our long essay series a few years (e.g., here) ago regarding the now-debunked “Hockey Stick” depiction of hemispheric and/or global temperatures. In 2001, the United Nations Intergovernmental Panel on Climate Change (IPCC) rolled out a depiction of temperatures over the past 1,000 years, and as seen below (Figure 1), the Medieval Warm Period and the Little Ice Age all but disappeared, and the warming rate of the most recent 100 years looked nothing short of incredible. The second plot below (Figure 2) comes from the most recent IPCC assessment, and note that (a) the plot is clearly labeled as “Northern Hemisphere,” (b) the recent warming looks less impressive, and (c) the Medieval Warm Period and the Little Ice Age periods are more prominent.

Defenders of these plots insist that the Little Ice Age was likely a regional phenomenon best seen in the mid-to-high latitudes of the Northern Hemisphere. However, a considerable debate continues in the scientific literature as to whether or not the Little Ice Age was a global or regional climate event. If the Little Ice Age was truly global in scope, then the temperature depictions presented by the IPCC underestimate the natural variability of Earth’s climate over the past 1,000 years.


Figure 1. Hockey stick representation of the northern hemispheric temperature used by the IPCC in the 2001 assessment.


Figure 2. Northern hemispheric temperature reconstruction from the 2007 IPCC report

Literally dozens of articles appear in the literature every month presenting clear evidence of the Little Ice Age, but critics are correct when they argue that most of the work comes from mid-to-high latitudes of the Northern Hemisphere. With that in mind, we at World Climate Report keep an eye out for evidence of the Little Ice Age from other parts of the planet, particularly locations far from the mid-to-high latitudes of the Northern Hemisphere. A recent article in The Holocene contains a title suggesting evidence of the Little Ice Age from southern Chile – a long way indeed from the mid-to-high latitudes of the Northern Hemisphere.

The article was generated by a research team from Chile’s Universidad de Concepción and the Pontificia Universidad Católica de Valparaíso. Araneda et al. begin their piece noting that “Of all the climatic changes during the Holocene, the recent cooling period, the ‘Little Ice Age’ (LIA), is one of the most broadly recognized events in the Northern Hemisphere. However, the duration and timing of the event has been disputed.” Furthermore, they note “A problem for the definition of the LIA is its variable timing and duration in different regions; thus, its synchronicity as a global phenomenon is still a matter of debate.” Once again, we learn that “debate” in climate change is still alive and well!

The research team states that “Chile has many historical records dating from Spanish colonial rule in the sixteenth century and it has been confirmed that these documents reliably date a succession of catastrophic events and provide a basis for reconstructing contemporary environmental conditions.” With that in mind, Araneda et al. decided to focus on the San Rafael glacier (see Figure 3) located on the northwestern margin of the North Patagonian Icefield (NPI)between 46° and 47° S (again, a long way from mid-to-high latitudes of the Northern Hemisphere).


Figure 3. Patagonian icefields of southern South America and the location of the San Rafael glacier (from Araneda et al., 2007)

The Spanish explorer Antonio de Vea arrived at the San Rafael on December 15, 1675, and as was the custom, the explorers left behind maps, diagrams, and descriptions of what they discovered. John Byron was shipwrecked near the glacier 67 years later, and he too described the position of the glacier, the fjords, and the existence of icebergs in the area. Twenty four years later, Jesuit priest JoséGarcia Alsué visited the area during a missionary campaign, and he also described the landscape in great detail, including the size of icebergs found in Laguna San Rafael. From these descriptions, Araneda et al. concluded that it was obvious that the glacier advanced considerably from 1675 to 1766 AD. In addition, Spanish explorer Francisco Machado visited the area in April of 1769 and mentioned snow on the ground at sea-level, suggesting a much colder climate than what is found there today. Araneda et al. note that “Previous research around the NPI has shown that many glaciers are currently retreating from maximum positions reached during the LIA” and that “Both tree-ring and lichenometric evidence indicate that the glacier reached its maximum position sometime before 1876, probably early in the second half of the nineteenth century.”

The research team concludes “The major contribution provided by the documentary evidence has been to confirm the occurrence of a cold period in the Laguna San Rafael area, which would be within the temporal window defined for the European LIA.” Furthermore, they conclude that “the sole historical evidence suggests that warm conditions prevailed around 1675, a date in which the front of the San Rafael glacier did not extend beyond the eastern shoreline of the lake. Later, a cooling period occurred from 1766 to 1898, with a peak between 1857 and 1871, during which the glacier advanced up to 8 km into the interior of the Laguna San Rafael. This cooling period declined after 1898, as evidenced by the decrease of the San Rafael glacier, which had retreated 1 km by 1904.” Most importantly to us at World Climate Report, they clearly state at the end “The recognition of the LIA in Northern Patagonia, through the use of documentary sources, provides important, independent evidence for the occurrence of this phenomenon in the region.”

There are those who will insist that the Little Ice Age was not a global event, but somehow, just as the Northern Hemisphere cooled during the Little Ice Age, glaciers were expanding in southern South America? Starting to sound global to us!

Reference:

Araneda, A., F. Torrejón, M. Aguayo, L. Torres, F. Cruces, M. Cisternas, and R. Urrutia. 2007. Historical records of San Rafael glacier advances (North Patagonian Icefield): another clue to ‘Little Ice Age’ timing in southern Chile? The Holocene, 17, 987-998.




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