University of Illinois plant biology and geology professor Feng Sheng Hu collected core samples from Alaskan lakes. The abundance and diversity of midges buried in sediments offers a reliable record of temperature fluctuations over time. Credit: Feng Sheng Hu
An analysis of the remains of ancient midges—tiny non-biting
insects closely related to mosquitoes—opens a new window on the past with a
detailed view of the surprising regional variability that accompanied climate
warming during the early Holocene epoch, 10,000 to 5,500 years ago.
Researchers at the University
of Illinois and the University of British
Columbia looked at the abundance and variety of midge larvae
buried in lake sediments in Alaska.
Midges are highly sensitive to summer temperatures, so changes in the abundance
of different species over time gave the scientists a reliable marker of
temperature fluctuations over the last 10,000 years.
Northern high latitudes are thought to have been warmer than
today during the early Holocene, a time of heightened solar irradiation as a result
of Earth’s axial tilt and orbit around the sun. The period is
often referred to as the Holocene Thermal Maximum. Scientists hope to
understand the ecological impacts of climate warming during that time to make
better predictions about the effects of future warming. But several decades of
research have yielded only ambiguous evidence of climate conditions in Alaska at that time.
The new analysis, conducted by University
of Illinois doctoral student Benjamin
Clegg with U. of I.
plant biology and geology professor Feng Sheng Hu, who led the study, offers
the first detailed record of temperature variation over the last 10,000 years
The analysis reveals that the region was significantly cooler than expected
during the early Holocene.
“This study shows that early Holocene warming did not
occur everywhere in high latitudes, and exhibited important regional
exceptions, even though the driving force behind it—solar input, in this case—was
geographically uniform,” says Clegg, who is now a postdoctoral researcher
in Hu’s laboratory.
The drivers of climate change during the early Holocene
“were different than the greenhouse gases responsible for global warming
today,” Clegg says. “So we should not expect to see exactly the same
spatial patterns of temperature anomalies in the next few decades as during the
The researchers hypothesize that solar warming during the
early Holocene spurred atmospheric circulation patterns that contributed to
extensive sea-ice off the Alaskan coast. That, and a treeless tundra
over more of the land area than at present would have increased surface
reflectivity, potentially contributing to the observed cooling, Clegg says.
“This study has important ecological and societal
implications,” Hu says. “Nonlinear responses such as those identified
here constitute a major source of potential climate ‘surprises’ that make it
more difficult to anticipate and prepare for future regional climate
The findings appear in the Proceedings of the National Academy of Sciences.