How Earth-Scale Engineering Can Save the Planet

3.Fertilize the ocean
Feasibility: 10
Cost: $
RISK: 9
On January 5, 2002, Revelle, a research vessel operated by the Scripps Institution of Oceanography, left New Zealand for the Southern Ocean-a belt of frigid, stormy seas that separates Antarctica from the rest of the world. There the scientists dumped almost 6,000 pounds of iron powder overboard and unleashed an armada of instruments to gauge the results.

The intent was to test a hypothesis put forth by oceanographer John Martin. At a lecture more than a decade ago, Martin declared: “Give me a half-tanker of iron, and I will give you an ice age.” He was alluding to the fact that the Southern Ocean is packed with minerals and nutrients but strangely devoid of sea life. Martin had concluded that the ocean was anemic-containing very little iron, an essential nutrient for plankton growth. Adding iron, Martin believed, would cool the planet by triggering blooms of CO₂-consuming plankton.

Oceanographer Kenneth Coale, who directs the Moss Landing Marine Laboratories near Monterey, California, was a chief scientist on the Southern Ocean cruise. He says the project was a success, proving that relatively small quantities of iron could spawn colossal blooms of plankton.

The Timeline
Scientists are wary, saying that too little is known about the deep-ocean environment to endorse further large-scale experiments. In October, Coale and other scientists will gather in New Zealand for a weeklong meeting sponsored by the National Science Foundation, New Zealand´s National Institute for Water and Atmosphere, and the International Geosphere-Biosphere Programme to decide how to proceed.

The Promise
Iron fertilization is by far the cheapest and easiest way to mitigate carbon dioxide. Coale estimates that just one pound of iron could conceivably hatch enough plankton to sequester 100,000 pounds of CO₂. “Even if the process is only 1 percent efficient, you just sequestered half a ton of carbon for a dime.”

The Perils
“What is still a mystery,” Coale says, “is the ripple effect on the rest of the ocean and the food chain.” One fear is that huge plankton blooms, in addition to gorging on CO₂, will devour other nutrients. Deep currents carry nutrient-rich water from the Southern Ocean northward to regions where fish rely on the nutrients to survive. Says Coale, “A fertilization event to take care of atmospheric CO₂ could have the unintended consequence of turning the oceans sterile. Oops.”

4. Turn CO₂ to Stone
Feasibility: 7
Cost: $$
RISK: 3
The Grand Canyon is one of the largest carbon dioxide repositories on Earth. Hundreds of millions of years ago, a vast sea covered the land there. The water, rich in carbon dioxide, slowly reacted with other chemicals to create calcium carbonate, or limestone-the pinkish bands striping the canyon walls today.

Nature´s method for turning CO₂ to stone is achingly slow, but researchers at the Goldwater Materials Science Laboratory at Arizona State University are working on a way to speed up the process. Michael McKelvy and Andrew Chizmeshya use serpentine or olivine, widely available and inexpensive minerals, as feedstock to fuel a chemical reaction that transforms CO₂ into magnesium carbonate, a cousin of limestone. To initiate the reaction-known as “mineral carbonation”-the CO₂ is compressed, heated, and mixed with feedstock and a catalyst, such as sodium bicarbonate (baking soda).

The Timeline
Scaling up the process to handle millions of tons of CO₂ would require huge quantities of serpentine or olivine. A single mineral-carbonation plant would carve out a mountain, but, McKelvy says, “You could carbonate [the CO₂] and put it right back where the feedstock came from.”

The Promise
Mineral carbonation is simply an accelerated
version of a benign natural process. The limestone in the Grand Canyon is 500 feet thick, McKelvy says, “and it has been sitting there not bothering anybody for millennia.”

The Perils
It costs roughly $70 to eliminate one ton of CO₂,
a price that McKelvy says is too high. Also, the feedstock
and CO₂ must be heated to high temperatures. “You wind up having to burn fossil fuels in order to provide the energy to activate the mineral to put away the CO₂,” he says.