Current Research in EEPS: Dr. Christo Buizert, Oregon State University
How cold was Antarctica during the last Ice Age?
The last ice age is the most recent natural example of large, global-scale climate change. It provides a natural experiment that we can use to learn more about the sensitivity of our climate system. Doing so requires accurate reconstruction of past temperatures.
Water stable isotope ratios in polar ice cores are a widely-used proxy to reconstruct past temperatures in the polar regions. The oldest ice cores have been drilled in East Antarctica, and go back 800,000 years in time. For these East Antarctic cores, traditional interpretation of water isotopes suggests the last glacial maximum (LGM) was ~9ºC colder than present. However, the water isotope thermometer is not very well calibrated, making such estimates uncertain.
Here we use borehole thermometry, firn-based reconstructions, and climate modeling to investigate the magnitude and spatial pattern of Antarctic LGM cooling. We find that West Antarctica cooled around 11ºC in our reconstructions, consistent with previous work on water isotopes. However, in East Antarctica our reconstructions suggest only 4 to 7ºC of cooling – for some of the ice cores we investigate, this is only about half of previous estimates.
Regional differences in our reconstruction primarily reflect surface elevation change. Climate models fit our reconstructions well when using realistic past ice sheet topography. By invoking changes to the strong near-surface atmospheric inversion in Antarctica, we can reconcile our new estimates with previous work. We conclude that traditional interpretation of water isotope records overestimates Antarctic surface temperature change, with implications for our understanding of high-latitude climate change, polar amplification, future Antarctic accumulation, and past warm periods.