Cracking the Ice Code

John Isbell, professor of geosciences

Cracking the Ice Code

UWM geologist John Isbell is looking for the natural rules that govern the Earth’s climate in the absence of human activity. His work is challenging many assumptions about the ways drastic climate change unfolds – and what to expect next.

What happened the last time the Earth’s climate shifted from “icehouse” to “hothouse”? And what does it tell us about climate change today?

John Isbell is on a quest to coax that information from the last time it happened on a vegetated Earth. The only problem is, that was between 290 and 335 million years ago. The information from the past forms the all-important baseline needed to predict what the added effects of human activity will bring.

During this period, the late Paleozoic Era, the modern continents were packed together in two huge supercontinents. One, called Gondwana, comprised most of the Southern Hemisphere, including what is now the South Pole, Australia, South America, India and Africa.

The work of Isbell, a specialist in late Paleozoic glaciation, has shaken the common belief that Gondwana was covered by one massive sheet of ice that gradually and steadily melted away as conditions warmed.

Isbell has determined that at least 22 individual ice sheets were located in various places over the region. And the state of glaciation during the period was unstable, marked by dramatic swings in climate and atmospheric carbon dioxide levels.

He has uncovered evidence that parts of eastern Australia were covered in ice during the tail end of the era, when the climate was warming, but not in polar Antarctica during the same period. He believes local events, such as mountain building, played a large role in the waxing and waning of glaciers during the transition.

“If we figure out what happened with the glaciers – and add it to what we know about other conditions, like carbon cycling, we will be able to unlock the answers to climate change.”

On one of his 15 trips to Antarctica, John Isbell took this shot of a graduate student enjoying the view of the Darwin Mountains.