To scientists who study lakes and rivers, it seems humans have embarked on a huge unplanned experiment.

By burning fossil fuels, we have already raised the concentration of carbon dioxide in the atmosphere by 40 percent, and we’re on track to increase it by much more. Some of that gas may mix into the world’s inland waters, and recent studies hint that this may have profound effects on the species that live in them.

“We’re monkeying with the very chemical foundation of these ecosystems,” said Emily H. Stanley, a limnologist (freshwater ecologist) at the University of Wisconsin — Madison. “But right now we don’t know enough yet to know where we’re going. To me, scientifically that’s really interesting, and as a human a little bit frightening.”

Scientists began taking continuous measurements of carbon dioxide in the atmosphere in the 1950s, and today they have more than six decades of consistent readings. In the 1980s, oceanographers followed suit, developing carbon dioxide sensors and deploying them across the planet.