How does rising atmospheric CO2 affect marine organisms?

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A Millennial-Scale Climatic Oscillation in Southern Chile
Fletcher, M.-S. and Moreno, P.I. 2012. Vegetation, climate and fire regime changes in the Andean region of southern Chile (38°S) covaried with centennial-scale climate anomalies in the tropical Pacific over the last 1500 years. Quaternary Science Reviews 46: 46-56.

The authors write that "it is of vital importance that we understand the nature, timing, impacts and regional expression of past periods of abrupt climate change if we are to place current and future climate trends into a meaningful historical context;" but they say that "to date, there is a heavy bias towards Northern Hemisphere records and comparatively little empirical evidence for concurrent climate intervals from the Southern Hemisphere landmasses," which inequality they hoped to reduce via their most recent research.

What was done
The two University of Chile scientists, as they describe it, "sampled and analyzed sediment cores from Laguna San Pedro (38°26'S, 71°19'W)," which they describe as "a small closed-basin lake located within the present-day distribution of Araucaria-Nothofagus forest in the Temperate-Mediterranean Transition zone in the Andes of Chile," where they focused on reconstructing the vegetation, climate and fire regime histories of the past 1500 years.

What was learned
The Chilean researchers found evidence for what they describe as "persistent cool/La Nina ENSO states" during the periods 1300-1000 and 725-121 cal yr BP, which they identify as the "Dark Ages Cold Period and Little Ice Age, respectively." In addition, they report finding evidence of "low relative growing season moisture and warmer temperature that correspond well with evidence for persistent warm/ El Nino ENSO states (1500-1300 and 1000-725 cal yr BP)," which they respectively associate with the Roman Warm Period and Medieval Climate Anomaly. Last of all, during the transition from the Little Ice Age to the Current Warm Period, which occurred from 121 cal yr BP (AD 1829) to the present, they found evidence for "a dramatic landscape alteration associated with the arrival of exotic taxa and an increase in burning," which they attribute to European colonization of the area.

What it means
Fletcher and Moreno state that "the palaeoenvironmental history inferred from Laguna San Pedro provides important palaeoclimatic information for this part of southern South America that is poorly represented in the palaeoclimate literature." And that information buttresses the ever-increasing likelihood that the natural climatic oscillation that has alternately brought the entire globe the Roman Warm Period, the Dark Ages Cold Period, the Medieval Warm Period and the Little Ice Age is also what has ushered us into the Current Warm Period. And that realization leads to the logical conclusion that earth's current level of not-so-unusual-warmth has likely had nothing to do with the historical increase in the air's CO2 content that has accompanied the rise and progress of the Industrial Revolution.

Reviewed 31 October 2012