New research from Scripps Institution of Oceanography
indicates glacial ice may have existed 91 million years ago during a period
known as the Cretaceous Thermal Maximum, when high ocean temperatures created a
“supergreenhouse” effect similar to today’s global warming.
The study, conducted by SIO researchers André Bornemann,
Oliver Friedrich and Richard Norris, counters commonly held assumptions that
the ice caps at Earth’s poles have always melted during past periods of intense
global warming.
Instead, it suggests that glaciers about half the size of
the modern Antarctic ice cap were present for about 200,000 years during the
thermal maximum, a period in which tropical ocean temperatures were higher than
today’s temperatures by about 10 degrees Fahrenheit.
Working as a postdoctoral scholar on the project in 2005,
Bornemann said he was surprised by the theory.
“When we started this project I was very skeptical about the
glaciation hypothesis,” he said in an e-mail. “But because of our excellent
data set which supports this idea, I became more convinced.”
The researchers used data from the preserved remains of tiny
marine organisms — known as foraminifera — dug from the western Atlantic
seafloor. Changes in ocean temperature and evaporation were tracked by
examining the different isotopes of oxygen stored in the microfossils.
The findings are also supported by research from other
institutions that concludes the sea level in the Cretaceous Period fell by
about 82 to 131 feet, indicating that water was removed from the oceans to form
glaciers.
However, Norris, a geology professor at SIO, said he is also
wary of the results.
“I remain skeptical of the presence of substantial ice in
the Cretaceous,” he said. “I believe our data, but I have been around long
enough to realize that even solid evidence can sometimes have an alternative
explanation I may not have thought about.”
Researchers have been unable to definitively confirm where
the large sheet of ice could have existed in the Cretaceous or how it was
formed.
“This is the most speculative part of this study,” Bornemann
said. “We have only the vague idea that ice should have formed on
which already was in polar position during the late Cretaceous.”
Norris postulated that the Cretaceous atmosphere would
likely hold more water, as evaporation and precipitation cycles accelerate in
warmer climates.
“As long as the climate got cold enough for snow to survive
… then there should have been plenty of snow to form ice,” he said. “Why there
was not always significant ice in the Cretaceous is speculative, but we think
the answer likely has to do with long period cycles in the shape of the Earth’s
orbit around the sun that cause slight variations in the amount of heat the
Earth gets.”
Norris said that the study, funded by the German Research
Foundation and the U.S. National Science Foundation, exposed the “trouble”
current computer models have when simulating the Cretaceous climate.
Additionally, although modern climate models indicate with some accuracy what
will occur within the next century, they may stop being effective if global
warming continues for more than a century or approaches Cretaceous-level
temperatures.
“Our models do a fairly good job simulating the modern
world, but fall down trying to simulate a much warmer climate,” Norris said.
“This problem suggests that there are still some basic dynamics about how the
climate system works that we have not incorporated in our models.”
SIO has six different research categories and a multitude of
ongoing projects. According to its Web site, “Research on Earth’s past climate
conditions is critical to predict what will happen as the planet’s climate
continues to warm.”
