Alaska Science Forum

A green system of carbon-dioxide removal

Fast-growing trees like these willows pull carbon dioxide from the atmosphere while adding oxygen.

Photo by Ned Rozell.

Last week, I wrote about a thought experiment proposed by Fairbanks scientist Jim Beget. He suggests raining down crystals of a compound that captures carbon dioxide onto a frigid plateau in Antarctica. There, the greenhouse gas might remain locked for a few hundred thousand years.

Beget will present his idea at the fall meeting of the American Geophysical Union this December in San Francisco. Alarming levels of carbon dioxide in the atmosphere are a frequent topic of discussion at the meeting, which will pull more than 20,000 scientists to California.

Dan Mann will also attend that meeting. Though the UAF geographer's presentation in San Francisco has nothing to do with carbon dioxide, he too has an idea how to remove some from the blanket of gases that surround our planet.

Mann suggests enhancing a carbon-dioxide removal system that has worked for a few billion years — the silent breath of plants.

Photosynthesis, the process by which plants convert sunlight to leaves and wood, involves a chemical reaction quite favorable for mammals like us. Plants suck up six molecules of carbon dioxide and combine it with six molecules of water and a spark of energy to produce one molecule of sugar. The plant uses the sugar to make, among other things, cellulose, the building material of stems and tree trunks. A byproduct of the photosynthesis reaction is six molecules of oxygen.

Mann thinks some geoengineering ideas are creative and fun and others are dangerous and arrogant. He thinks the Earth itself has an answer in the greenery that graces much of its land surface.

"Why monkey around trying to improve on a CO2-drawdown process that has functioned very well indeed for 2.4 billion years?" Mann wrote in an email message. "Plants are nonpolluting (unless you are an anaerobic microbe) and grow almost everywhere. Just add water and sun."

Trees are storage cylinders of carbon. Humans are cutting them down at a rate equal to 36 football fields every minute (more than 50 thousand square miles of forest every year). Researchers with the World Wildlife Fund observe that one half of the world's forests from 1,000 years ago are now gone. In many areas, those lost forests inhaled and stored much more carbon than the farms that replaced them.

To do some calculations, Mann pulled out a notebook and opened a carbon footprint calculator on his computer. He figured an acre of fast-growing pines planted in a New Zealand sheep pasture takes up five to 10 tons of carbon dioxide every year. Those trees wear the carbon as trunks, twigs, leaves and roots.

"In comparison, flying roundtrip from Fairbanks to San Francisco to attend the AGU conference has a carbon footprint of around 0.6 tons of CO2," Mann wrote. "So you could theoretically fly about 10 times and be free of dreaded global-warming guilt if you had planted and cared for an acre of pine trees on land that had been previously carbon-bare, like in a former sheep pasture."

Mann owns land in New Zealand and spends time there during Fairbanks' winter. Asked whether he had planted his own acre of trees there, he nodded.

"Seventeen of them."

Since the late 1970s, the director of the Geophysical Institute at the University of Alaska Fairbanks has supported the writing and free distribution of this column to news media outlets. This is Ned Rozell's 20th year as a science writer for the Geophysical Institute.

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