David Fields of the Monterey Bay Aquarium Research Institute has a paper in tomorrow’s Science (press release here) suggesting an interesting anthropogenic warming fingerprint: plankton in varves on the ocean floor. Both warm- and cold-water forams can be found, and the relative abundances of the various types works as a climate proxy.
Fields sees the “regime shift” of the mid-1970s (most famously called the Pacific Decadal Oscillation), and suggests that the patterns in the sediments from the late 20th century are unprecedented in the 1,400-year record. In other words, 20th century warming is fundamentally different than variations seen during that period, with “a deep, penetrative warming not observed in previous centuries.”
(Hat tip me.)