CLIMATE

Earth Raises Its Beach Umbrella

Do Phytoplankton Help Regulate Planetary Temperature?

While you may have never heard of dimethylsulfide, chances are you’ve smelled it before. One of the many ingredients that gives the ocean its characteristic scent, dimethylsulfide, or, as it’s more commonly known by its abbreviation, DMS, has not garnered much attention from researchers in recent years, despite its climatic significance. The scientific basics are this: An increase in carbon dioxide emissions could help stimulate more phytoplankton blooms, resulting in more DMS being produced and ventilated into the atmosphere. While DMS is not a greenhouse gas like carbon dioxide, its properties do reflect heat away from the planet.

Save for some new findings and spirited debate among the scientific community, the sulfurous gas, which some believe could play a vital role in mitigating climate change, has been overshadowed by its more infamous colleague, carbon dioxide. With efforts to slow the rapid accumulation of greenhouse gases at a virtual standstill in many parts of the world and clean energy technologies in their early stages of deployment, some scientists are optimistic about Earth’s ability to regulate its climate through the production of DMS and other natural processes. But before DMS becomes the next darling of geoengineering proponents, it’s worth understanding both this chemical’s place in the marine ecosystem and the point that the planet cannot fix the manmade problem of global climate change. Moreover, the planet cannot fix itself while humans continue to generate greenhouse gases unabated.

Relying solely on nature to rectify man’s mistakes will not be sufficient.

James Lovelock first articulated the DMS-climate link in the early 1970s. Lovelock is a renowned scientist and the originator of the Gaia hypothesis—which holds that the planet is a single large organism that self-regulates in order to maintain optimal conditions.^[1] Though Lovelock and his colleagues theorized that DMS, which is produced by phytoplankton, provided the missing link to explain the elevated levels of sulfate aerosols emissions above the sea surface, they initially lacked the appropriate mechanism to account for it.^[2]

Upon being excreted by phytoplankton, some fraction of DMS finds its way into the atmosphere, where, through oxidation, it forms sulfate aerosols, while the remainder is broken down by microbial activity in the water column. At a loss to explain how these aerosols helped moderate the climate, Lovelock turned to Robert Charlson, a chemist at the University of Washington, who suggested that they formed cloud condensation nuclei, or CCN—small particles that act as centers for the condensation of water to form cloud droplets. A higher concentration of cloud droplets would increase the reflectivity of marine clouds, blocking a portion of solar radiation and causing a slight cooling of the atmosphere. The presence of clouds over the oceans, which cover roughly 70 percent of the planet’s surface area, is more important climatically because they absorb a majority of the sun’s heat.

Charlson’s hypothesis was bolstered by satellite images that showed cloud plumes intensifying due to the addition of smoke particles from ships. Scientists already knew that marine clouds could become brighter, and therefore more reflective, if they had more particles. This breakthrough led to the publication of a seminal paper in which Lovelock, Charlson, and two colleagues proposed that DMS may have helped cool the Earth during past periods of high solar radiation or increasing greenhouse gases—serving, in effect, as the planet’s thermostat.^[3]

Now, with greenhouse gases once again on the rise, some scientists believe DMS production could pick up, providing a natural check on climate change. How effective a check it proves to be, especially in light of the pace at which we are consuming fossil fuels, remains to be seen; specifics about how much DMS is presently in the atmosphere and how quickly it moves there are still poorly understood. Some believe DMSP, or dimethylsulfoniopropionate—the precursor of DMS—is used by phytoplankton to regulate the salinity and temperature within their cells or to repel predators; others think phytoplankton convert DMSP to DMS in response to stress from UV radiation—the sulfur compound helps remove reactive molecules that cause damage from their cells.

Lovelock and Chris Rapley, the director of London’s Science Museum, recently put forth a scheme that would harness the phytoplankton’s increased productivity by installing large arrays of vertical pipes that would mix nutrient-rich deep water with surface waters. This, they argue, would cause more blooms and, in turn, speed up the production of DMS—essentially hitting two geoengineering birds with one stone. They are currently advising Atmocean, a startup that is developing such a technology. Supporters of ocean iron fertilization, a scheme in which iron sulfate particles are dumped into the ocean to stimulate blooms, have also latched onto this idea.

But as I’ve written about previously on Science Progress, such ecological tinkering could be the cure that is worse than the disease. While these proposals to assist natural temperature regulation could eventually show promise, many researchers believe it is still too early to tell whether natural processes alone can put a damper on climate change. Reducing the amount of heat reaching the oceans could change wind patterns or decrease surface water mixing, potentially cutting down the amount of nutrients available for phytoplankton to grow. And reducing the amount of sunlight reaching the planet could slash global precipitation levels, possibly leading to more droughts. Moreover, 200 countries at the U.N.’s Convention on Biological Diversity, citing the unknown risks, voted in May for a moratorium on projects that aim to spur algae growth in the oceans. Finally, these geoengineering proposals won’t stop other impacts of increased carbon in the atmosphere, like ocean acidification.

Because scientists still do not fully understand the DMS cycle, they are worried that they could be missing out on an important intermediary or process—which could throw a wrench into their predictions. In the end, relying solely on nature to rectify man’s mistakes will not be sufficient; while the planet has a role to play, it is simply too risky to hope Mother Earth, even with a little extra push, will clean up after our actions. Reducing our greenhouse gas emissions is the only guaranteed way to fix the problem.

Jeremy Jacquot is a graduate student in marine environmental biology at the University of Southern California and is a contributing writer for VentureBeat, DeSmogBlog and TreeHugger.

Notes

[1] J. Lovelock, Gaia: A New Look at Life on Earth (Oxford University Press, USA, 2000).

[2] R. A. Kerr, “No Longer Willful, Gaia Becomes Respectable,” Science, 240(1998): 393–395.

[3] R. J. Charlson, J. E. Lovelock, M. O. Andreae & S. G.Warren, “Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate,” Nature, 326 (16) (1987): 655 – 661.

Tags: Climate Change, oceans

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