How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

The Paleoclimate of the USA's San Francisco Bay Watershed
Malamud-Roam, F.P., Ingram, B.L., Hughes, M. and Florsheim, J.L. 2006. Holocene paleoclimate records from a large California estuarine system and its watershed region: linking watershed climate and bay conditions. Quaternary Science Reviews 25: 1570-1598.

What was done
The authors conducted an extensive review of "the variety of paleoclimatic resources for the San Francisco Bay and watershed in order to identify major climate variations in the pre-industrial past, and to compare the records from the larger watershed region with the Bay records in order to determine the linkages between climate experienced over the larger watershed region and conditions in the San Francisco Bay."

What was learned
Malamud-Roam et al. report that "intermittent mega-droughts of the Medieval Climate Anomaly (ca. AD 900-1350) coincided with a period of anomalously warm coastal ocean temperatures in the California Current," and that "oxygen isotope compositions of mussel shells from archaeological sites along the central coast also indicate that sea surface temperatures were slightly warmer than present [our italics]." In contrast, they note that "the Little Ice Age (ca. AD 1450-1800) brought unusually cool and wet conditions to much of the watershed," and that "notably stable conditions have prevailed over the instrumental period, i.e., after ca. AD 1850, even including the severe, short-term anomalies experienced during this period," namely, "the severe droughts of the 1930s and the mid-1970s."

What it means
In this particular part of the world, peak medieval warmth appears to have exceeded peak modern warmth. Also, as the four researchers note, when longer paleoclimate records are considered, "current drought conditions experienced in the US Southwest do not appear out of the range of natural variability." However, as they opine, "warmer temperatures associated with anthropogenic global warming may exacerbate such conditions," which also suggests that, even now, it is still not as warm as it was back in the Medieval Warm Period.

Reviewed 12 November 2008