Geophys. Res. Lett.http://doi.org/htw (2012)

Cool climatic conditions between AD 1400 and 1800 — a period known as the Little Ice Age — have been well documented in temperature reconstructions from the Northern Hemisphere. Borehole data from West Antarctica show that this cooling also extended to the high southern latitudes.

Anais Orsi and colleagues at the Scripps Institution of Oceanography in California reconstructed the temperature of snow on the surface of the West Antarctic ice sheet over the past 1,000 years. They combined calibrated borehole data from the flow divide of the Western Antarctic ice sheet with modelling to reconstruct the timing and magnitude of the temperature change. The data show an unusually cold period centred around AD 1600, with average temperatures approximately half a degree colder than those of the past 100 years. Cooling during this time is further supported by changes in bubble density and water isotopes previously reported from ice cores at this site.

The coincidence of cooling in both the Northern and Southern Hemispheres is inconsistent with a bipolar seesaw model for this recent climate shift. Instead, the team argues that the cool interval can be best explained by low solar irradiance and frequent volcanic eruptions at that time.