How to Cool the World Without Blocking the Sun
Microbes may help shape our climate future
In the fall of 1993, a ship entered the Pacific Ocean carrying nearly 1,000 pounds of iron crystals packed in barrels and then dumped it all into the waves. The next morning, the water turned a soft green color thanks to the newly sprouted phytoplankton. Microorganisms that require iron to grow absorb carbon dioxide from the air during their metabolism. Scientists already knew that the Earth's atmosphere was filled with this gas and that the planet would soon need cooling. So why not grow more tiny creatures that could help? John Martin, the oceanographer who pioneered the idea, said, “Give me half a tanker of iron and I'll give you an Ice Age.” (He was joking, of course, but not 100%.)
Fertilizing the ocean with iron is a form of geoengineering, a set of technologies that are both exciting for their potential to significantly alter Earth's systems and controversial for the same reason. Currently, some geoengineering techniques such as spraying chemicals in the sky to encourage clouds to produce more rain and alleviate drought are already being used. Scientists have begun real demonstrations of “cloud brightening”: they “sprinkle” the sky sea salt to increase the amount of sunlight reflected by the clouds. And even more controversial approaches – for example, injecting brilliant sulfur compounds into the stratosphere to blocking sun rays — are becoming part of mainstream climate debates. All of these methods have uncertain effectiveness, are associated with unknown risks and may lead to undesirable consequences.
As the planet warms, geoengineering is poised for unprecedented manipulation of it, whether researchers are inventing machines to suck greenhouse gases from the atmosphere or nudge microorganisms to do it for them. Interacting with house plankton seems like a less drastic approach than, say, planting a massive umbrella in space to shade the planet from the light of her star. But the field is so new that scientists don't yet know whether geoengineering with microorganisms would actually be a gentler form of climate intervention. Microbes, after all, play a huge role in the world around us and inside us – I should count among the co-authors of this story the trillions of microorganisms living in my body. To keep Earth habitable, scientists must understand exactly how the microscopic creatures around us can be beneficial and perhaps even preferable to more fanciful approaches to cooling the planet.
Microbes, the most abundant organisms on Earth, have been cleaning up human messes since time immemorial and, more recently, helping to support modern life. They decompose the contents of landfills, clean water bodies of pollution, decompose pollutants in wastewater treatment plants and corrode oil spills. However, in large-scale climate solutions, microbes are “woefully underutilized and completely overlooked,” Lisa Stein, a professor of biological sciences at the University of Alberta, told me. Stein says microbes are largely ignored in the Intergovernmental Panel on Climate Change's reports on future climate scenarios. But she and other scientists say they can play an important role in the fight against man-made climate change.
One of the favored approaches uses methane, an extremely potent greenhouse gas that is responsible for 30 percent of global temperature rise. Mary Lidstrom, professor emeritus of chemical engineering and microbiology at the University of Washington, is working to genetically modify bacteria that naturally consume methane as a food source, so that the microbes extract even more of the gas from the air. Bacteria known as methanotrophs will live inside units known as bioreactors, which resemble shipping containers. Such bioreactors can be placed near known sources of methane—landfills, coal mines, oil and gas wells, and wetlands—to minimize the amount of methane released into the air. They can purify gas that is already circulating in the atmosphere, says Stein, who is also the Canada Research Chair in Climate Change Microbiology. The science is still in the early stages, but one day “this could change the rate at which our thermometer rises,” she said. Researchers can also use carbon-eating microorganisms living in soil that contains more carbon than the atmosphere, changing the composition of the soil to increase the bacteria's metabolic capacity.
Carbon-metabolizing bacteria may also be useful in the ocean. Matthew Sullivan, a professor of microbiology at Ohio State University, studies marine viruses that infect such microbes and influence how they process carbon. “I’m a big believer in taking advantage of the billions of years of work that nature has already done,” Sullivan told me. It's possible, he said, that certain viruses could push these bacteria to convert carbon into its most severe forms. Ideally, the bacteria would clump together and sink to the ocean floor, taking the carbon with them so it can't raise global temperatures.
Scaling up any kind of climate engineering is not easy. For example, to significantly slow the warming caused by methane, 50,000 to 300,000 Lidstrom bioreactors would be needed to operate over 20 years. And the subsequent effects are difficult to predict, let alone contain. A substance introduced into the soil on one piece of land can enter a completely different ecosystem through runoff or other means and upset its happy balance. Likewise, the influx of iron into the South Pacific could have consequences for other regions of the world's seas. Jay Lennon, a biology professor at Indiana University Bloomington, told me that interfering with viruses could also have undesirable consequences: “Will there be a corresponding bloom of viruses that will kill all that phytoplankton and spew carbon dioxide back into the atmosphere?” Ruth Warner, a professor of biogeochemistry at the University of New Hampshire, told me that such questions are important to consider, but human intervention is constantly affecting the lives of Earth's microbes. For example, every use of fertilizer in agriculture is considered to have microbial exposure. “We have already done our manipulations in these places,” Varner said.
Much attention has been paid to the possibility of unintended consequences of geoengineering, but almost as much uncertainty exists about the intended effects. Scientists don't know for sure how powerful many of these concepts will be, including those that have already been tested outside the laboratory. Ship expeditions in the 1990s, for example, didn't last long: Travel was expensive, and scientists couldn't stay at sea to determine what exactly was going on below the surface, David Kirchman, a marine biologist at the University of Delaware, told me. To achieve maximum effect, he said, the carbon removed from the atmosphere must remain buried for at least a century. However, it is possible that if phytoplankton do not sink to sufficient depth, “they will simply be eaten by organisms in the surface layer of the ocean, and CO2 will return to the atmosphere.”
Scientists have not conducted large-scale experiments to enrich the ocean with iron since 2012, but these studies may soon resume. A pair of researchers are using new funding from the National Oceanic and Atmospheric Administration to model the effectiveness of the technique. With no sea travel on the horizon, microbial research could quickly find itself on the same precipice as other forms of geoengineering work. Real control of the Earth's future lies beyond climate hacks, in a real transition away from fossil fuels. But the hotter the planet gets, the more attractive geoengineering will seem. “Unless we make large-scale changes in the behavior of people around the planet, then at the current rate of events, it seems that we will be forced to resort to engineering solutions,” says Sullivan. We may have to decide sooner than we think which divine levers, big or small, we need to pull.”
