evidence: After 30 years of research, the question itself hasn’t changed, but the reasoning behind it couldn’t be more different. Oceanographers started out wanting to know if the ocean was keeping up with the amount of carbon dioxide people are putting into the atmosphere. Instead, they found that people aren’t the only players changing the ocean carbon cycle. Over decades, natural cycles in weather and ocean currents alter the rate at which the ocean soaks up and vents carbon dioxide. What’s more, scientists are beginning to find evidence that human-induced changes in the atmosphere also change the rate at which the ocean takes up carbon. In other words, it turns out that the world is not a simple place. [...] "When we started in the 70s and 80s, we had this concept: we’ll measure [carbon dioxide concentrations in the ocean] 10 years later, and we’ll just see the anthropogenic input," says Feely. "We had very simplistic ideas that the anthropogenic changes would be the only changes we would see," he adds a little ruefully. [...] A scientist uses a torch to seal glass ampoules containing dissolved gases extracted from seawater. Tens of thousands of samples were collected during the Climate Variability and Predictability cruises. Scientists were surprised when decades of sampling revealed a complex relationship between man-made carbon dioxide emissions, cyclical changes in climate, and the oceanic carbon cycle. (Photograph ©2008 Brett longworth.)