How does rising atmospheric CO2 affect marine organisms?

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Ocean Temperatures (The Past Several Millennia) -- Summary
Just as peering deep into the heavens gives us a better perspective of our place in the cosmos, peering deep into our planet's past provides a better understanding of what may have produced its unique thermal history. In this brief summary, we thus review the findings of several studies that have employed this approach in the hope of discerning what role ancient variations in the air's CO2 content may or may not have played in determining earth's past climatic behavior, concentrating on proxy-derived sea surface temperatures or SSTs.

Gagan et al. (1998) used a double-tracer technique based on Sr/Ca and 18O/16O ratios in the skeletal remains of corals from Australia's Great Barrier Reef to infer climatic conditions for that region of the earth about 5350 years ago. Impressed with their use of such coupled data, which allowed them to more accurately determine SSTs than had been possible in the past, Beck (1998) stated in his commentary on their paper that the new approach "promises to elucidate many important new clues about the dynamics of the coupled ocean-atmosphere-climate system for climate modelers to digest." In fact, Gagan et al.'s work did so immediately, indicating that the tropical ocean surface some 5350 years ago -- when there was a whole lot less CO2 in the air than there is currently -- was 1.2C warmer than the mean that prevailed throughout the early 1990s. This finding accorded well with terrestrial pollen and tree-line elevation records from elsewhere in the tropical Pacific for the entire period from 7000 to 4000 years ago. In addition, their work suggested that the higher tropical SSTs of that time likely enhanced evaporation from the tropical Pacific, and that the extra latent heat and moisture thereby exported to higher latitudes may have helped to maintain the equable climates known to have characterized the extra-tropics during this time period.

Taking a much greater leap back in time, McManus et al. (1999) examined a deep-sea sediment core from the eastern North Atlantic Ocean that included the last five glacial-interglacial cycles. In doing so, they noted significant temperature oscillations throughout the record, which were of much greater amplitude during glacial as opposed to interglacial periods. SSTs, for example, oscillated between 1 and 2C during warm interglacials, but varied between 4 and 6C during colder glacial times. On the basis of these findings, they concluded that climatic variability on millennial time scales "has thus been the rule, rather than the exception." And with such a long and unfailing period of precedent, it is highly likely that the warming of the last century or so was simply the most recent manifestation of a naturally recurring phenomenon that had nothing to do with the concurrent increase in the atmosphere's CO2 concentration. In addition, McManus et al.'s findings clearly contradict the climate-alarmist contention that any future global warming will result in greater -- and, therefore, harsher -- temperature extremes; for the half-million-year real-world record clearly indicates that temperature variability during warmer times is more muted than it is during colder times.

Adding another 50,000 years to the time interval investigated by McManus et al., Herbert et al. (2001) analyzed proxy SSTs over the past 550,000 years via data obtained from several marine sediment cores obtained along the western coast of North America, from 22N at the southern tip of the Baja Peninsula to 42N off the coast of Oregon, finding that "the previous interglacial produced surface waters several degrees warmer than today," such that "waters as warm as those now at Santa Barbara occurred along the Oregon margin." In fact, their data indicate that the peak SSTs of the current interglacial were 1 to 4C cooler than the peak SSTs of all four of the preceding interglacial periods (when, again, there was much less CO2 in the air than there is today).

Finally, reaching back in time beyond a thousand millennia, Raymo et al. (1998) studied various physical and chemical characteristics of an ocean sediment core retrieved from a site south of Iceland. This work revealed that millennial-scale oscillations of climate were occurring well over one million years ago in a region of the North Atlantic that has been shown to strongly influence circum-Atlantic, and possibly global, climate. These oscillations appeared to be similar in character and timing to the Dansgaard-Oeschger cycles of the most recent glacial epoch. However, because the climate of the early Pleistocene was too warm to support the growth and development of the large 100,000-year ice sheets characteristic of the late Pleistocene, and because similar millennial-scale climate oscillations are evident in both time periods, they concluded that millennial-scale climate oscillations "may be a pervasive and long-term characteristic of earth's climate, rather than just a feature of the strong glacial-interglacial cycles of the past 800,000 years." Hence, since the millennial-scale climate oscillations of both periods have not been attributed to variations in atmospheric CO2 concentration, there would appear to be little reason to attribute the warming of the past century or so to the concurrent increase in the atmosphere's CO2 concentration, or to expect that any further rise in the air's CO2 content would trigger any significant warming.

In view of these several findings, it would thus appear that the global warming that constituted the Little Ice Age-to-Current Warm Period transition was nothing more than a run-of-the-mill manifestation of the faithfully-recurring millennial-scale oscillation of climate that has been responsible for alternately bringing us several-century-long cool and warm intervals throughout glacial and interglacial periods alike, which going back further in time include the Medieval Warm Period, Dark Ages Cold Period, Roman Warm Period and so forth. The air's CO2 content has been merely a passive responder to what really rules the planet's climate system, which to this day still remains ill-defined.

References
Beck, W. 1998. Warmer and wetter 6000 years ago? Science 279: 1003-1004.

Gagan, M.K., Ayliffe, L.K., Hopley, D., Cali, J.A., Mortimer, G.E., Chappell, J., McCulloch, M.T. and Head, M.J. 1998. Temperature and surface-ocean water balance of the mid-Holocene tropical western Pacific. Science 279: 1014-1017.

Herbert, T.D., Schuffert, J.D., Andreasen, D., Heusser, L., Lyle, M., Mix, A., Ravelo, A.C., Stott, L.D. and Herguera, J.C. 2001. Collapse of the California Current during glacial maxima linked to climate change on land. Science 293: 71-76.

McManus, J.F., Oppo, D.W. and Cullen, J.L. 1999. A 0.5-million-year record of millennial-scale climate variability in the North Atlantic. Science 283: 971-974.

Raymo, M.E., Ganley, K., Carter, S., Oppo, D.W. and McManus, J. 1998. Millennial-scale climate instability during the early Pleistocene epoch. Nature 392: 699-702.

Last updated 27 May 2009