Climate: New study of paleoclimate record confirms warming

Data from coral, caves and sediment layers reflects temperature increases measured by surface instruments

By Summit Voice

FRISCO — A team of federal and university scientists say they’ve compiled a set of temperature records from ice cores, old corals, and lake sediment layers that closely matches the pattern of global warming from 1880 to 1995 recorded by thermometers.

The paleoclimate record also confirms that warming accelerated between 1980 and 1995 compared to the long-term trend, starting in 1880. The record also reflects small-scale features within the long-term trend, including a 1940s warm interval 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.

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.”

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