Human Carbon Emissions Using Up Oceans' Absorption Capacity

WASHINGTON, DC, July 15, 2004 (ENS) - Humans have used up about one-third of the potential of the world's oceans to absorb the greenhouse gas carbon dioxide generated by human activities such as burning coal for electricity and gasoline for transportation.

The first comprehensive study of the ocean storage of carbon dioxide derived from human activities - anthropogenic CO2 - determined that the oceans have taken up some 118 billion metric tons of this carbon dioxide between 1800 and 1994.

The international team of scientists who completed the survey said this total is approximately one-third of the oceans' long-term potential.

The research team, which included scientists from the United States, South Korea, Australia, Canada, Japan, Spain, and Germany, based the study on a 10 year survey of global ocean carbon distributions in the 1990s.

The global survey combined measurements of carbon dioxide and other ocean factors such as temperature, salinity, oxygen, nutrients and chlorofluorocarbon tracers in the Atlantic, Pacific and Indian oceans.

Caribbean Sea off Mona Island, Puerto Rico (Photo courtesy NOAA)

"If the ocean had not removed 118 billion metric tons of anthropogenic carbon between 1800 and 1994, the CO2 level in the atmosphere would be about 55 parts per million greater than currently observed," said Christopher Sabine, an oceanographer at the National Oceanic and Atmospheric Administration's Pacific Marine Environmental Laboratory and the lead author of one of the papers.

The studies are critical to research of global warming, which the vast majority of scientists believe is occurring because greenhouse gases, including CO2, are released into the atmosphere primarily by the burning of fossil fuels.

Today's CO2 levels are reaching 380 parts per million in the atmosphere. By contrast, analysis of ice cores determined that for the 400,000 years before the industrial revolution began in the 1800s, atmospheric CO2 concentrations remained between 200 and 280 parts per million.

Sabine explained that because the ocean mixes slowly, the anthropogenic CO2 from the atmosphere is generally confined to the upper layers of the ocean.

"About half of the anthropogenic CO2 taken up over the last 200 years can be found in the upper 10 percent of the ocean," he said. "The ocean has removed 48 percent of the CO2 we have released to the atmosphere from burning fossil fuels and cement manufacturing."

There are two large reservoirs that are capable of taking significant amounts of CO2 out of the atmosphere: the ocean and land plants.

Studies over the last decade have indicated that the land plants are taking up CO2 at rates comparable to the oceans, but scientists have determined that over a 200 year time frame, land plants have released more of the gas to the atmosphere than they have taken up.

Waves breaking as seen from a porthole on the NOAA research vessel Nathaniel B. Palmer crossing the Southern Ocean. (Photo by Michael Van Woert courtesy NOAA)

The uptake of anthropogenic CO2 by the oceans changes their chemistry and potentially can have significant impacts on the biological systems in the upper oceans, according to the scientific team.

Their research showed that a substantial amount of the calcium carbonate shells produced in surface waters dissolves in the upper ocean.

This in turn reduces the ability of many species of marine organisms to produce protective calcium carbonate shells and could impact marine food webs.

Recent studies have shown that calcification rates can drop by as much as 25 to 45 percent at CO2 levels equivalent to atmospheric concentrations of 700 to 800 parts per million.

Today's levels are 380 parts per million, but scientists say that level could double by the end of the century if fossil fuel consumption continues as projected.

"This research presents the first complete synthesis of modern global ocean inorganic carbon measurements," said James Yoder, director of the National Science Foundation's ocean sciences division.

This new global data set of ocean-carbon system observations, cosponsored in the United States by NOAA, the National Science Foundation, and the Department of Energy, is unprecedented with more than 72,000 carbon measurements, 10 times more observations than the previous global survey in the 1970s and 10 times more accurate, Yoder said.

The data are drawn from three major research programs - the World Ocean Circulation Experiment, the Joint Global Ocean Flux Study, and NOAA's Ocean-Atmosphere Carbon Exchange Study.