Extending Climate Records Beyond Instrumental Measurements
Paleoclimate studies extend records of climate beyond the time period for which we have instrumental measurements. Such research not only answers questions about what Earth was like in the past, but also provides context for the climate changes that we are experiencing today and informs our understanding of how climate is likely to change in the future. In 2013, an international team of researchers published the most comprehensive reconstruction of past temperature changes ever generated at the continental scale. The reconstruction, published in the journal Nature Geoscience,7 confirms an overall cooling trend across nearly all continents during the last one to two thousand years. Recent warming, beginning in some regions at the end of the 19th century, reversed this trend. The study found that temperature variations were more similar within hemispheres than between the Northern and Southern Hemispheres, and that anomalous periods such as the Little Ice Age (ca. 1350–1850) and Medieval Warm Period (ca. 900–1300) were detectable but did not show a globally synchronous pattern across multiple decades.
This research was led by the International Geosphere-Biosphere Programme’s (IGBP’s) Past Global Changes (PAGES) project, which is supported in part by NSF, NOAA, and USGCRP’s funding for IGBP. The temperature reconstruction was produced by combining data from tree rings, pollen, corals, sediments, ice cores, stalagmites, and historical documents at hundreds of locations across seven continents. As part of PAGES, researchers from USGS and academia are recon-structing continental-scale patterns of hydrologic variability over the last few thousand years, which, combined with the temperature reconstruction, will shed light on the response of ecosystems to climate variability over periods of years to centuries. To learn more, visit: http://goo.gl/I8s9S8