How Glaciers Can Produce Long-Term Warming

As glaciers grind up rocks, they change the chemistry of the water streams that run from them, and eventually that of the ocean. Compared to rivers, its seems their net effect is acidic. Paul Quackenbush

Ice and snow are well known for cooling things down. In the long term, however, glaciers can warm the Earth up, a new paper reveals.

Snow’s short-term effects on climate are straightforward. White reflects sunlight back into space, while surfaces bare of ice cover absorb more radiation. The loss of ice (or its darkening with soot) means more heat gets absorbed, potentially creating a runaway warming effect, contributing to our current troubles.

However, Dr Mark Torres of Rice University has shown in the Proceedings of the National Academy of Sciences that there can also be a warming effect from glaciers, albeit one that works at a more glacial pace.

A quick look at the fjords of Norway shows the immense impact glaciers can have on local geography. Torres investigated the effect that the weathering glaciers produce as they slide over rocks. Glaciers increase oxidation of carbonates and pyrite, also known as fool's gold, producing acid run-off that eventually flows into the sea, making the oceans more acidic. Torres found this effect dominates over the breaking down of silicates, which produce alkaline run-off.

Rivers also wear rocks down, but Torres compared the behavior of the world's surviving glaciers with river catchments and concluded ice is a more potent acidifier than liquid water. Indeed, the more of a catchment area glaciers cover, the more the balance tilts towards acid run-off.

Mark Torres with some of the bags he used to collect runoff from glaciers and river catchments to measure for acidity. Rice University

"The ocean stores a lot of carbon," Torres said in a statement. "If you change the chemistry of the ocean, you can release some of that stored carbon into the atmosphere as carbon dioxide.”

Torres estimates that over a 10,000-year period, glacial expansion could have added an extra 25 parts per million to the carbon dioxide in the atmosphere. That's only about a fifth of what humans have added since the start of the Industrial Revolution (and over a period 50 times as long), but it is still enough to trigger a noticeable warming of the planet.

The work offers a possible explanation for how our planet has avoided runaway cold or hot temperatures. Climate scientists have been puzzled as to why widespread glaciation never becomes locked in as a result of so much light being reflected back to space. Although cycles in the Earth’s orbit are sufficient (allowing for amplifying affects) to explain some returns to more temperate climates, others are harder to explain. The release of extra carbon dioxide could have been enough to break winter’s grip.

Early in Earth’s history, the lack of oxygen in the atmosphere would have suppressed this oxidative weathering, reducing long-term carbon dioxide release and explaining evidence for a near total global “snowball” prior to 2.1 billion years ago.



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