Scientists expect sea level to go up by 3 feet or so by the end of this century, thanks mostly to changes in the great ice sheets that dominate Greenland and Antarctica – but they worry about unknown factors that might drive ice into the sea faster than projected. Now a pair of MIT scientists has identified what might, in theory, turn out to be one of these ‘unknown unknowns.’
In a study released Wednesday in the Journal of Physics D: Applied Physics, Zhao Qin and Markus Buehler show that carbon dioxide, the main cause of global warming, can make ice more fragile and prone to cracking. This could mean, in principle anyway, that the extra CO2 pumped into the atmosphere by the burning of fossil fuels could make glaciers fragment more easily, and not just melt more quickly. And that could accelerate sea level rise, endangering people and property around the world.
The fragmentation is still largely theoretical, Buehler explained in an interview. “We look at tiny crystals of ice. Glaciers are much, much larger, so our research might or might not be relevant at that scale. We’re not addressing climate change in this paper,” Buehler said.
Climate change was, however, part of the inspiration for the research. Buehler and Zhao have studied the phenomenon of fracturing in materials ranging from metal to ceramic to spider silk. In many of these, fractures happen when some impurity shatters the hydrogen bonds that give the material its strength.
Hydrogen bonds also hold ice crystals together, and Zhao – noting that huge chunks of glacier occasionally break off in both Antarctica and Greenland – suggested they look at ice as well. “We realised,” Buehler said, “that this might be relevant to geoscientists who want to understand how these pieces behave.”
They didn’t use actual ice, but instead relied on a computer simulation to see what happened when a crack in a virtual ice crystal is invaded by molecules of carbon dioxide. Many materials naturally have microscopic cracks, and when impurities lodge there – salt molecules in concrete, CO2 molecules in ice – they can break the hydrogen bonds that hold things together. That’s what happened to the ice in the scientists’ simulations. “We created an ice crystal and put in some CO2,” Buehler said. The tiny crack spread and widened.
Buehler reiterated that this may or may not happen to a glacier-size chunk of ice in the real world. “The levels of CO2 we used in the simulation are much higher than the concentrations in the atmosphere,” he said. Buehler’s work also doesn’t address the question of how CO2 molecules would get into the ice; in a simulation, you just put the molecules where you want them.
But in the simulation, at least, you don’t need much CO2 to get things going. “Even just a single molecule,” Buehler said, “can lead to the nucleation [that is, the start] of a fracture.”
“I hope that this might lead to more studies of ice fracturing,” he said. “It might be interesting to look at.”
Given the potential significance of the new research for the future of planet, "might be interesting" is pretty clearly an understatement.