Untested claim: increased CO2 helps glacier ice to crack

From the Institute of Physics , something so overreaching I just can’t believe the Institute of Physics would put out a press release on it.  Where does one start with stuff like this? This is all modeling, they haven’t even tested any actual sea ice to see if it follows the theory. Their premise would be easy to test with some glacier water, a freezer, a controlled gaseous CO2 source, and a tensile/ductile strength mechanical force tester for brittleness. But that sort of basic testing wasn’t done. Yet, they equate their modeled posited effect to be the cause of the Pine Island Glacier breakoff, as if somehow events like that never happened before CO2 was at 392PPM.  Note the abstract and link to the paper below. – Anthony

The well-documented presence of excessive levels of carbon dioxide (CO2) in our atmosphere is causing global temperatures to rise and glaciers and ice caps to melt.

New research, published today, 11 October, in IOP Publishing’s Journal of Physics D: Applied Physics, has shown that CO2 molecules may be having a more direct impact on the ice that covers our planet. 

Researchers from the Massachusetts Institute for Technology have shown that the material strength and fracture toughness of ice are decreased significantly under increasing concentrations of CO2 molecules, making ice caps and glaciers more vulnerable to cracking and splitting into pieces, as was seen recently when a huge crack in the Pine Island Glacier in Antarctica spawned a glacier the size of Berlin.

Ice caps and glaciers cover seven per cent of the Earth—more than Europe and North America combined—and are responsible for reflecting 80 per cent of the Sun’s light rays that enter our atmosphere and maintain the Earth’s temperature. They are also a natural carbon sink, capturing a large amount of CO2.

“If ice caps and glaciers were to continue to crack and break into pieces, their surface area that is exposed to air would be significantly increased, which could lead to accelerated melting and much reduced coverage area on the Earth. The consequences of these changes remain to be explored by the experts, but they might contribute to changes of the global climate,” said lead author of the study Professor Markus Buehler.

Buehler, along with his student and co-author of the paper, Zhao Qin, used a series of atomistic-level computer simulations to analyse the dynamics of molecules to investigate the role of CO2 molecules in ice fracturing, and found that CO2 exposure causes ice to break more easily.

Notably, the decreased ice strength is not merely caused by material defects induced by CO2 bubbles, but rather by the fact that the strength of hydrogen bonds—the chemical bonds between water molecules in an ice crystal—is decreased under increasing concentrations of CO2. This is because the added CO2 competes with the water molecules connected in the ice crystal.

It was shown that CO2 molecules first adhere to the crack boundary of ice by forming a bond with the hydrogen atoms and then migrate through the ice in a flipping motion along the crack boundary towards the crack tip.

The CO2 molecules accumulate at the crack tip and constantly attack the water molecules by trying to bond to them. This leaves broken bonds behind and increases the brittleness of the ice on a macroscopic scale.

Carbon dioxide enhances fragility of ice crystals

Zhao Qin and Markus J Buehler 2012 J. Phys. D: Appl. Phys. 45 445302 doi:10.1088/0022-3727/45/44/445302

Abstract:

Ice caps and glaciers cover 7% of the Earth, greater than the land area of Europe and North America combined, and play an important role in global climate. The small-scale failure mechanisms of ice fracture, however, remain largely elusive. In particular, little understanding exists about how the presence and concentration of carbon dioxide molecules, a significant component in the atmosphere, affects the propensity of ice to fracture. Here we use atomic simulations with the first-principles based ReaxFF force field capable of describing the details of chemical reactions at the tip of a crack, applied to investigate the effects of the presence of carbon dioxide molecules on ice fracture. Our result shows that increasing concentrations of carbon dioxide molecules significantly decrease the fracture toughness of the ice crystal, making it more fragile. Using enhanced molecular sampling with metadynamics we reconstruct the free energy landscape in varied chemical microenvironments and find that carbon dioxide molecules affect the bonds between water molecules at the crack tip and decrease their strength by altering the dissociation energy of hydrogen bonds. In the context of glacier dynamics our findings may provide a novel viewpoint that could aid in understanding the breakdown and melting of glaciers, suggesting that the chemical composition of the atmosphere can be critical to mediate the large-scale motion of large volumes of ice.

Introduction

Ice caps and glaciers cover 7% of our planet, greater than the land area of Europe and North America combined [1]. They reflect 80–90% of the solar radiation and trap a large

amount of carbon dioxide. Specifically, the Arctic accounts for 10–15% of the earth’s carbon sink [2]. The glaciers’ dynamical behaviour and stability play important roles in controlling the global climate [3, 4]. Thereby, the facture mechanism of ice is of paramount importance for the understanding of glacial dynamics [5], and at a fundamental level is controlled by how a single crack propagates in ice crystals via the

breaking of chemical bonds [6]. Such growth of cracks eventually mediates the breakdown of ice, as exemplified in recent incidents of large-scale fracture of glaciers [7, 8]. Very

large-scale ice fractures occurred recently close to the Pine Island Glacier in the Antarctic region, which generated an iceberg with an area of around 880 square kilometres, the size

of the city of Berlin [9].

While the macroscopic mechanical properties of pure ice are well understood by laboratory tests and its behaviour has been characterized by existing fracture

mechanics models [10], the effect of environmental conditions such as the concentration of carbon dioxide, have not been incorporated into existing models. Lack of such knowledge prevents us from understanding how changes in the chemical environment affect the stability and movement of glaciers, which is important given the rising levels of carbon dioxide in the atmosphere.

[Suggestion: do some laboratory testing to get the same level of understanding]

…

Conclusion

Using atomic simulations with the ReaxFF reactive force field, we investigated the effect of carbon dioxide on the fracture behaviour of ice. We find that the material strength

and fracture toughness are decreased significantly under increasing concentrations of carbon dioxide molecules. This phenomenon is caused by the interaction between water and carbon dioxide molecules. Carbon dioxide molecules first adhere to the crack boundary by forming hydrogen bonds, and then migrate along the crack boundary towards the crack tip.

The dissociation energy of hydrogen bonds at the crack tip is decreased under the attack by carbon dioxide. This migrationattacking process repeats itself and renders the ice crystal more brittle by mediating crack propagation. Our theoretical model quantitatively accounts for the effect of carbon dioxide on the surface energy and fracture toughness of ice. It could be instrumental for further studies of ice fracture in various chemical environments and may be scaled up by incorporating it into models of glacier dynamics.

paper here (you may need to register for free account to read it)

http://iopscience.iop.org/0022-3727/45/44/445302/pdf/0022-3727_45_44_445302.pdf

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