29 January 2015

Early 20th Century Global Warming Linked to Tropical Pacific Wind Strength


Nearly 30% of the global warming since 1900 occurred between 1910 and 1940, when increases of human-produced CO2 played a relatively minor role in global climate change.  Recently it has been demonstrated that naturally-occurring decadal variability associated with the Interdecadal Pacific Oscillation (IPO) can drive the globally averaged temperature signal.  This is because periods of westerly trade wind anomalies in the tropical Pacific are associated with warmer equatorial Pacific SSTs, a positive phase of the IPO, and a faster rate of global warming.  Could internal naturally-occurring climate variability in the tropical Pacific have contributed to the early century warming?   Answering this question is made difficult because there are few measurements of surface winds or equatorial Pacific sea surface temperatures in the first part of the 20th century.  Here we look fill that data gap by studying tropical Pacific corals to infer trade wind direction, SSTs, and the phase of the IPO.   Westerly wind anomalies trigger strong physical mixing and release of Mn from lagoonal sediments, which is then incorporated into the coral skeleton. A new reconstruction of trade wind strength derived from Mn/Ca in a western Pacific coral suggest that weaker Pacific trade winds contributed to a positive phase of the IPO and rapid global warming between 1910 and 1940.

D M Thompson
National Center for Atmospheric Research (NCAR)
Thompson, DM, JE Cole, GT Shen, AW Tudhope, and GA Meehl.  2014.  "Early 20th Century Global Warming Linked to Tropical Pacific Wind Strength."  Nature Geoscience, doi:10.1038/ngeo2321.