Last March, for instance, a team led by Shaun Marcott at Oregon State University used climate proxies to build a global temperature record reaching back 1,200 years – one that also noted the pre-1900 cooling trend.
Until now, however, the proxy approach has been used to reconstruct changes in global-average and hemisphere-wide temperatures, Dr. Kaufman explains.
"There was very little information about past climate variability at the regional scale," he says. Yet the team notes that no one lives in a global-average world. People live in specific regions where geography plays a vital role in shaping the climate patterns they experience.
The team omitted Africa from its analysis because the proxy records are too few to be useful. Instead, the researchers looked at seven continent-scale regions in South America, the southwestern Pacific (including Australia), as well as North America, Europe, Asia, Antarctica, and the Arctic.
This approach reveals a more complex picture over various intervals than a record of global average or hemispheric temperatures would present, the researchers find.
The team also notes that their work likely understates the overall intensity of warming because the reconstruction record stops short of the record-setting warm years and the warmest decade on record that have occurred since 1990.
On millennial time scales, the cooling trend was statistically significant on all continents except North America, where the cooling was weaker, according to the study.