19 July 2012
One of several last-ditch fixes proposed to fight climate change, iron dumping has long been proposed as a “geoengineering” strategy—a way to manipulate the climate to reduce the effects of heat-trapping greenhouse gases.
Some studies, however, have suggested that, over time, iron fertilization can create low- to no-oxygen conditions—dangerous for marine life—or trigger blooms of types of plankton that are harmful to some organisms. (See “Plan to Dump Iron in Ocean as Climate Fix Attracts Debate.”)
The new study, though, finds no evidence for these concerns. Instead, most of the plankton in iron-enriched waters falls to the seafloor and gets buried in ocean sediments, which trap carbon long-term, the study found.
For the study, scientists in 2004 added seven tons of iron sulfate to 58 square miles (150 square kilometers) of ocean off Antarctica—chosen for its “central role” in the global carbon cycle, according to study co-author Christine Klass, of the Alfred Wegener Institute for Polar and Marine Research.
The iron spurred a bloom of diatoms, algae that form large, slimy groupings with high sinking rates. In this case more than 50 percent of a plankton bloom typically sank to the seafloor.
Though the study authors have spent years verifying the results, they remain cautious.
So far, the data suggest iron fertilization could trap only about 10 percent of current carbon dioxide emissions “under very, very optimistic assumptions,” study co-author Dieter Wolf-Gladrow, also of the Wegener institute, said by email.
Iron seeding, he added, “cannot provide a solution for our CO2 problem.”
Klass agreed: “Given the many uncertainties and potential side effects of this technique, more experiments would be necessary before large-scale application.”
Beyond iron fertilization, scientists have proposed building artificial volcanoes to pump bits of sulfur-heavy material, similar to volcanic ash, into the atmosphere. Like ash from real volcanoes the particles bounce the sun’s light and heat back into space.
This and other emergency measures were under the microscope in 2010 as part of the first Asilomar International Conference on Climate Intervention Technologies in Pacific Grove, California. The meeting drafted the world’s first voluntary guidelines for ethical behavior in geoengineering schemes.
That’s not to say any of the schemes will be deployed in the near future, Samuel Thernstrom, co-director of the Geoengineering Project at the American Enterprise Institute, a Washington, D.C.-based policy-research institute, noted in 2010.
But experts should seriously consider all options, Thernstrom said, including altering the climate: “There is no argument for ignorance—we should know more about geoengineering.”
It may be a cousin to pond scum, but seaweed has attained a more noble status among scientists advocating seaweed farms as carbon sinks (above, a woman in Bali, Indonesia, harvests seaweed in an undated photo).
Half of the world’s photosynthesis—a process that uses sunlight to convert carbon dioxide into energy—takes place in the oceans. But most of that occurs in tiny marine plants called phytoplankton, which can’t be farmed, according to the Seaweed Clean Development Mechanism Project at Korea’s Pusan National University.
Enter seaweed, which can be easily cultivated along coasts—a possible solution for scientists looking to boost the oceans’ carbon-zapping contribution. (Related: “Earliest Known American Settlers Harvested Seaweed.”)
As a bonus, farmed seaweed can be harvested and turned into a renewable fuel—”a joint benefit,” Michael MacCracken, chief scientist for climate programs at the nonprofit Climate Institute, a Washington, D.C.-based climate-advocacy organization, said in 2010.
“Biochar” in soils
It may be old as dirt, but the Amazonian practice of making “biochar” could be a climate saver, experts say (pictured, a farmer holds biochar in West Virginia in 2008).
When returned to the soil, biochar—a rich, highly porous charcoal made by heating agricultural waste—can trap carbon in soils for hundreds to thousands of years, according to the International Biochar Initiative. By contrast, the carbon-holding powers of trees are limited, because greenhouse gases escape if a tree is cut down or dies.
The American Enterprise Institute’s Thernstrom puts biochar in his “deserves to be explored” category, as does the Climate Institute’s MacCracken, who noted that the substance has the added benefit of improving soil quality.
Greening the desert
Greening the desert may be a way to trap more atmospheric greenhouse gases such as carbon dioxide, experts say—a geoengineering idea already taking root in Africa.
For instance, 13 African countries are building a “Great Green Wall” of trees that would gobble up carbon while halting the Sahara’s spread. And organizers of the ambitious Sahara Forest Project plan to plant trees alongside their massive renewable energy complexes, which are intended for deserts around the globe.
If greenhouse gas emissions continue to skyrocket, however, a green desert likely wouldn’t have enough carbon-trapping heft to make a dent, said the Climate Institute’s MacCracken. But in a lower-carbon world, he said, green deserts could be a good strategy for keeping emissions down.
With a design reminiscent of an oceangoing pogo stick, this “cloud ship” may give some bounce to geoengineering efforts to combat climate change.
The wind-powered devices take in ocean water and spray a fine mist of sea salt, which generates ocean clouds. Such clouds are denser and whiter than regular clouds, so they reflect more of the sun’s heat back into space.
Deploying about 1,500 of these relatively inexpensive vessels could have an immediate cooling effect, said the American Enterprise Institute’s Thernstrom.
“We’re a long way from knowing for sure whether that would work,” he said. “But it’s a plausible theory that does deserve serious investigation.”
Fighting climate change is hardly black-and-white. But making roofs more reflective by painting them white—like these rooftops in Hamilton, Bermuda—may be one of the simplest geoengineering fixes.
Dark roofs reflect about 10 to 20 percent of sunlight, whereas so-called cool roofs send about 70 to 80 percent of the sun’s rays back into space, according to researchers at California’s Lawrence Berkeley National Laboratory.
What’s more, white roofs boast an added climate boon: Reflective-roofed buildings don’t get as hot on the inside, reducing the need for air conditioning, the Climate Institute’s MacCracken noted.