UCSB Study Chronicles Global Warming’s Effect on Oceans
by Nick Welsh
UCSB professor David Siegel is the scientific equivalent of the seasick sailor: He’s a green-about-the-gills oceanographer. Twenty years after the fact, Siegel — now 47 — still shudders to remember the horrors he suffered during a five-week scientific ocean-faring expedition with Scripps Institute back when he was a UC San Diego student. At the time, Siegel was studying to become an engineer. But most of the jobs in his field involved making bombs or working for the Department of Defense, neither of which was acceptable to Siegel. And despite the intense bodily distress inflicted by his early oceanic research, he fell hopelessly in love. “You could say I was hooked,” he recalled.
Siegel’s big challenge lay in figuring out how to study the oceans without setting foot in a boat. For Siegel — a funny guy and a self-described nerd — that salvation lay in the form of global satellites. About 14 years ago, he began the first of his many collaborations with NASA, the federal space agency whose numerous satellites allow researchers to expand the scope of their inquiries in ways previously unimaginable. Rather than traveling in stomach-churning vessels whose top speed might equal a bicycle’s, Siegel can now monitor the entire globe in two days, “moving” 100 kilometers almost in the blink of an eye.
For the past 15 years, Siegel has been involved with a research effort, sponsored by NASA, to determine the effects of temperature changes on the productivity of the oceans, or the extent to which ocean life flourishes. Using photos taken during an eight-year period from a global satellite built by Raytheon on Hollister Avenue and launched from Vandenberg Air Force Base, Siegel and crew examined the effect temperature changes had on phytoplankton, tiny microscopic sea plants that serve as essential food for all oceanic life. Two weeks ago, Siegel and his team went public, publishing their findings for the first time in the pages of the prestigious scientific journal Nature. Given the report’s significance in the global warming debate, the group’s findings have been picked up by most mainstream media outlets and given extensive airplay on National Public Radio.
Boiled down to its bare bones, the report concludes that there is almost certainly a direct and powerful connection between water temperature and phytoplankton health. From sea to sea, Siegel found that as the ocean waters warmed, phytoplankton populations dropped and seas turned bluer; when the waters cooled, phytoplankton populations increased and seas turned greener.
Siegel said that in some ways he was not surprised by the results, terming them “almost obvious.” He noted, for example, that in Santa Barbara, ocean water turns much greener and algae blooms under the cooling influence of “June gloom.” But what stunned and surprised Siegel was the extent to which that same trend held true for all 14,000 data collection points located in every ocean across the globe. “We could aggregate all the places of the ocean and show numerically that there was a relationship between temperature and the ocean’s productivity,” he said. “We saw that regularly and we saw that glaringly.” For example, he said, due to the influence of La Niña during the first two years of the study — 1996 and 1997 — oceans were generally cooling off and becoming greener. But from 1998 to 2004 — the last year of data collection — oceans have generally increased in temperature and blueness and decreased in productivity.
Siegel said he was surprised not just by the universality of the relationship between temperature and productivity, but by the strength of the relationship. Of the many mysterious factors that could influence oceanic productivity, Siegel said temperature proved unusually powerful. “I had my suspicions beforehand what the trend would be,” he said, “but I was astounded by how tight the coupling was.”
What makes Siegel’s work so important in the global warming discussion is not that he discovered the oceans were heating up at a faster rate than anyone thought; he didn’t. In fact, Siegel said, some parts of the ocean are still cooling off. Rather, the real importance of his findings lies in the universality of the temperature/productivity link, coupled with how vital phytoplankton are to the web of life on planet Earth. “Obviously this is speculative, but if we ratchet down on the fish food being naturally produced, we might also be ratcheting down on the number of fish out there to eat,” Siegel said.
And phytoplankton are not only the essential unit in the oceanic food chain, but also account for roughly one-half of the planet’s photosynthesis, the process by which plants convert sunlight into energy. In that process, plants take in carbon dioxide and “exhale” oxygen. If oceans absorb less carbon dioxide than they used to, then presumably there will be more of it left in the atmosphere, which could accelerate the pace of global warming. Experts estimate that the planet’s oceans have warmed by about one degree Fahrenheit in the past 100 years. “What happens in 2050 when ocean temperatures might increase by two degrees?” Siegel asked. “Plant life in the ocean will certainly suffer.” But if and when that happens, Siegel will have provided future scientists a solid baseline of reliable data from which to measure the decline.
Siegel is quick to stress that he was just one participant in a broad multidisciplinary effort, working to increase the scientific understanding “one brick at a time.” But his peers at UCSB, like paleoclimatologist Professor David Lee (who was uninvolved in the project), credited Siegel for figuring out the mathematical algorithms necessary to accurately translate the green picked up from the space satellite — indicating phytoplankton’s green chlorophyll — into a reliable indicator of the plant’s health and vitality. These calculations involved placing a delicate optical instrument on the tip of a spacecraft and sending it hurtling into space, then sifting through a tidal wave of visual information, some of which had been distorted by radiation, particulate matter in the atmosphere, and even clouds. “Dave’s been a real pioneer in developing the methodology that lets the satellites detect these changes in color,” said Lee. “It’s a very good study. It doesn’t mean that the ocean’s ecosystem is about to crash, but it’s another way of recognizing and quantifying how we’re messing with something on a really grand scale.”
The scientific reason why a warming trend means trouble for oceanic plant life is that it restricts the mixing of shallow waters — where the phytoplankton live — with the colder, deeper waters that contain nutrients necessary for phytoplankton to thrive. The greater the difference in temperature between the two layers, the less likely it is that hotter surface waters will make the plunge down to where the nutrients are, and vice versa. Simply put, global warming leads to a more stratified ocean.
The oceanic effects of global warming have been recognized by some scientists and businesses, which are seeking to remedy it by artificially reconnecting the upper and lower strata — thereby jumpstarting the growth of phytoplankton. One company has proposed doping the water with iron, one of the nutrients essential to phytoplankton’s survival. In exchange, it hopes to lay claim to the increased carbon dioxide that would be absorbed into the ocean as a result of the thriving phytoplankton. Such “carbon offsets” are now the subject of intense speculative interest. But given that phytoplankton have a life span of only two days, it’s hard to know how effective such a scheme would be — or to predict its possible side effects.
Siegel for one was skeptical. “I go to meetings and I hear people saying these things,” he said. “I know there’s venture capital involved in such things, but I’m tempted to check their reflexes to make sure they’re not stoned.”