Latest Study Reconstructs Earth’s Climate History: Temperatures Varied by Region
As climate studies saturate scientific
journals and mainstream media, with opposing viewpoints quickly squaring off in
reaction and debate, new findings can easily be lost in the noise.
But in the case of Darrell Kaufman,
Northern Arizona University Regents’ Professor in Quaternary Geology and
Climate Science, and a study appearing in Nature
Geoscience, obscurity is an unlikely fate.
What Kaufman—the lead co-author of
“Continental-Scale Temperature Variability during the Last Two Millennia”—and
78 experts from 24 countries have done is to assemble the most comprehensive
study to date of temperature change of Earth’s continents over the past 1,000
to 2,000 years.
By looking regionally, the
researchers found considerable complexity hidden within a global average. “We
wanted a new and ambitious effort to reconstruct past climate,” Kaufman said of
the PAGES 2k network of researchers. “One of the
strongest aspects of the consortium study is that it relies on regional
Members of the consortium represent
eight continental-scale regions. They lent their insights about the best proxy
records—such as tree-ring measurements—to use for a particular region, and how
to interpret the data based on regional climatology.
While the study does not attempt to
attribute temperature changes to natural or human-caused factors, Kaufman said
the finding of a long-term global cooling trend that ended late in the 19th
century is further evidence that increased greenhouse gasses have had an
influence in later years.
“The pre-industrial trend was likely
caused by natural factors that continued to operate through the 20th century,
making 20th century warming more difficult to explain if not for the likely
impact of increased greenhouse gasses,” Kaufman said.
While that sounds like a familiar
theme, the study’s findings of regional variations are less well known. Because
of extensive participation by scientists working in the Southern Hemisphere,
Kaufman said, data from those regions broadened what had been a view previously
centered on Europe.
“We know the most about the
long-term temperature history in Europe, but we find that not every region
conforms with that pattern,” Kaufman said. He noted that temperatures varied by
region against the backdrop of the long-term cooling identified by the study.
The regional focus on the past 2,000
years is significant for two reasons, Kaufman said. First, climate change at
that scale is more relevant to societies and ecosystems than global averages.
And second, “regional scale differences help us to understand how the climate
system works, and that information helps to improve the models used to project
Kaufman’s own research team added to
the strong regional input. His research in Alaska and elsewhere formed part of
the dataset. “The questions that my team hopes to address involve the larger
climate system, and our research contributes one piece of the global puzzle,”
In another of the study’s major
contributions, the entire database on which it was based has been tabulated and
will be made available publicly for further analysis. Kaufman and his co-authors
have posted the data along with frequently asked questions about the study on
the PAGES project website.
“My co-authors and I look forward to
seeing the data used by others in future analyses because science moves forward
with well-informed alternative interpretations,” Kaufman said.
--Courtesy of NAU News