Carlsbad Caverns, captured by photographer Ansel Adams. Scientists can extract temperature records from the chemistry of layers in stalagmites and stalactites, corals, layered ocean sediments, ice cores, and other paleo proxy records. A new compilation of these paleo "proxies" reveals a pattern of global warming in the last 130 years that's similar to the thermometer record. Credit: Department of the Interior. National Park Service.

A new compilation of temperature records etched into ice cores, old corals, and lake sediment layers reveals a pattern of global warming from 1880 to 1995 comparable to the global warming trend recorded by thermometers. This finding, reported by a team of researchers from NOAA’s National Climatic Data Center, the University of South Carolina, the University of Colorado, and the University of Bern in Switzerland, resolves some of the uncertainty associated with thermometer records, which can be affected by land use changes, shifts in station locations, variations in instrumentation, and more.

“Using only temperature-sensitive paleoclimate proxy records, un-calibrated to instrument data, it is possible to conclude that the warming trend in the global surface temperature record is supported by independent evidence,” said David Anderson, head of the Paleoclimatology Branch at NOAA’s National Climatic Data Center and lead author of the paper. The new research is detailed in “Global Warming in an Independent Record of the Past 130 Years,” published online this week in Geophysical Research Letters.

Check out this YouTube video by NOAA's Paleoclimatology Branch explaining their analysis.

The thermometer-based global surface temperature record provides meaningful evidence of global warming over the past century, and it is critical to have independent analyses, like this one, to verify that record. For this analysis, the team used environmentally sensitive proxies to compile a temperature record that is independent of thermometer-based records. Proxies such as coral growth layers, shells of tiny marine plankton, lake sediments, ice cores, and caves are biologically, physically, or chemically connected to environmental conditions. For example, coral skeletons and plankton shells record temperature changes in the ratio of oxygen isotopes.

This paleoclimate dataset used 173 independent proxy datasets to draw a record from 1730 to 1995. To ensure the paleoclimate dataset was independent of the instrumental record, the scientists used raw data rather than reconstructed temperatures. Paleoclimate records and trends are affected by multiple environmental influences, not just warming, and the scientists minimized non-temperature influences by averaging together many records.

“The correlation of this paleoclimate dataset with the global surface temperature record has important implications in climate science and provides evidence of the significance of paleoclimate research,” said Thomas Karl, Director NOAA’s National Climatic Data Center. “Temperature reconstructions, like this one, continue to play a significant role in understanding the global climate by quantitatively extending the record back in time in an independent, objective way.”

In addition to their shared long-term trend, many smaller-scale features also appear in both the paleoclimate and instrument temperature records. For example, the warm interval of the 1940s in the global surface temperature record also appears in the paleoclimate record. Both records also show that the global warming in the last 15 years of the record (1980–1995) is significantly faster than that of the long-term trend (1880–1995).