The World’s Oldest Carbon Experiment

Chesapeake Bay salt marshes help predict effects of elevated atmospheric CO2 levels

A few miles outside Washington, D.C., a team of scientists from the Smithsonian Institution are predicting the impact elevated atmospheric carbon levels could have on our world. That’s nothing new, as scientists around the world work on the same problem every day. But what sets their work apart is what they’re studying to make predictions: a Chesapeake Bay salt marsh.

This virtual “climate crystal ball” is the nation’s longest-running experiment to measure CO₂ levels, and is predicting what plant life will look like by 2100 if atmospheric CO2 levels continue to rise. energyNOW! chief correspondent Tyler Suiters looked at how the Smithsonian Environmental Research Center has been duplicating the effects of rising CO2 levels on a small-scale, then forecasting what it means for plant ecosystems over the past two decades.

You can watch the full segment by clicking the video below:

The experiment focuses on a series of miniature greenhouse enclosures, built over the grassy Chesapeake salt marshes. CO₂ is pumped into the enclosures to simulate different atmospheric concentrations that could be possible given current and potential emissions levels, and observe how the marshes are affected. “Inside this chamber, the carbon dioxide concentration of the atmosphere, is what the whole marsh will be growing in at the end of the century,” said Patrick Megonigal, a Smithsonian biogeochemist.

One clear effect has been a change in which plants can grow in the environment. While higher CO₂ levels are theoretically better for plants that convert it to energy, the scientists have seen a change in the plants growing with higher atmospheric carbon, especially when comparing photos of the environment when the experiment began. “You can see the species shift in this picture,” said Gary Peresta, a Smithsonian environmental engineer. “When we started it was all grass, and now you see all the sedges (a type swamp grass) moved in there.”

The experiment’s duration also shows potential for natural carbon sequestration – to a point. The salt marshes used in the experiment date back to the early 18^th century, and have been storing carbon all that time. “It’s a carbon sink,” said Megonigal. “Everything that’s brown in here was gas in the atmosphere that the plants took out, and when they died, it got buried.”

But current manmade emissions levels are higher than the Earth has ever seen, and plants have a limited capacity to convert CO₂, limiting the net sequestration effect. While the future of emissions isn’t decided yet, this equation has led the scientists to one conclusion. “We’ll have more carbon in the atmosphere,” said Megonigal. “I’ll put the house on that one.”