By Stephanie Paige Ogburn and ClimateWire, Source: Scientific American

The amount of carbon dioxide in the tropical Pacific Ocean has increased surprisingly quickly over the past 14 years, according to new research from scientists at the National Oceanic and Atmospheric Administration and the University of Washington.

The reason for the rapid increase in carbon dioxide concentrations is a combination of natural variability and human-caused emissions of carbon dioxide into the atmosphere, said Adrienne Sutton, a research scientist with NOAA’s Joint Institute for the Study of the Atmosphere and Ocean at the University of Washington.

Although it is difficult to tease out exactly how much of the increase in carbon dioxide concentrations is due to human-caused climate change, “we assume that most of the carbon dioxide increase [in the tropical Pacific] is due to anthropogenic CO₂,” Sutton said.

In fact, the rate of increase in carbon dioxide concentrations in parts of the tropical Pacific Ocean, a band of ocean along the equator between the coasts of South America and Southeast Asia, is greater than the rate of increase of atmospheric carbon dioxide.

Measurements by atmospheric scientists at NOAA show that atmospheric CO₂ is increasing at a rate of about 2 parts per million per year. But in parts of the tropical Pacific, the rate of change in CO₂ concentrations measured by the researchers reached 3.3 ppm per year.

“It was a big surprise. We were not expecting to see rates that strong,” Sutton said.

Current models do not predict such large increases in carbon dioxide concentrations in that part of the ocean, which is one of the reasons those findings were unexpected. The data were collected from a set of seven buoys in the tropical Pacific, starting in 1998.

Because that part of the ocean is dominated by many natural cycles, including the El Niño Southern Oscillation and the Pacific Decadal Oscillation, the researchers had to work to disentangle the overall signal of carbon dioxide concentrations from the variability caused by natural changes.

“One of the reasons why we were really interested in putting these CO₂ systems on the buoys was so that we could see the incredible natural variability that occurs in this region,” Sutton said.

For the first few years of data collection, the researchers saw a clear signal of carbon dioxide growth rates changing as the ocean switched from El Niño to neutral to La Niña.

Read the full article at: Scientific American