Stalagmites indicate climate trouble ahead, Cornell professor says

Rhawn Denniston's perspective on climate change comes from studying stalagmites, some 25,000 years old.

Based on the data he gleans from these mineral deposits in caves, the Cornell College paleoclimatologist says the outlook is not good unless humans make big changes. Soon.

The data, when applied to general circulation models, suggests that unless heat-trapping carbon dioxide emissions are reduced, Iowans will experience hotter summers and more frequent severe storms and flooding.

There's no upside to those scenarios, which are the topic of discussion this month by representatives of nearly 200 nations at the Copenhagen climate summit. Iowa could benefit, however, from efforts to mitigate future climate change if policymakers make the right choices, Denniston said.

For example, Iowa could be the “Saudi Arabia of renewable energy” if it continues to develop its biofuels and wind energy potential, said Denniston, who has a doctorate in environmental studies. Those measures can help the state and world avoid the worst consequences of climate change, he added.

Scientists believe global warming is caused by an increase of pollutants in the atmosphere, including carbon dioxide, which acts like a blanket trapping heat in the atmosphere and warming our climate.

Denniston studies the stalagmites - conical mineral deposits gradually built upward from cave floors as ground water seeps through and drips from the cave's roof - to reconstruct past climates.

A wooden table in his Geology Center office on the Mount Vernon campus is covered with stalagmites, some as old as 25,000 years, which he gathered in June from northern Australian caves. In the 90-degree caves, he encountered poisonous bugs, snakes and a 4-foot-long carnivorous monitor lizard.

The stalagmites have been cut lengthwise to show annual growth bands similar to tree rings. The bands indicate periods of heavy rainfall as well as droughts, Denniston said. The climate signals are in the oxygen and carbon isotopes of the calcium carbonate that makes up the stalagmites.

“We can get at things like when El Ninos were more common and intense, when precipitation was more strongly seasonal, when it was hotter, when the monsoons were stronger, how fast climates changed and how climates in one place seem to affect climates in other places,” Denniston said.

The stalagmites show a relationship between rainfall, Greenland ice core temperatures and Chinese monsoons, he said. When plotted against timelines, stalagmites show extended droughts have corresponded with the fall of Chinese dynasties. That suggests to Denniston that climate change - past and future - has social, economic and political consequences.