Can you imagine what the world would look like if you took Earth's carbon dioxide levels from before the Industrial Revolution and doubled them?

Actually, no one can. That's because no one knows exactly how carbon dioxide fits into all of Earth's processes. That's why scientists use Free-Air Carbon Enrichment (FACE) to essentially turn up the knob on ambient carbon dioxide and create an artificial atmosphere of the future. Aspen FACE in northern Wisconsin surrounds nine forest plots, each about the size of a baseball infield, with hoses that spray CO2 on the trees. By cranking up the CO2 to 560 parts per million (an optimistic guess for 2050 levels), they see how a mini ecosystem adapts to the change.

But unlike other FACE sites, Aspen also turns up the amount of ozone (the major ingredient of smog) around the trees. Among other things, they are finding that CO2 boosts growth, ozone retards it, and pests seem to enjoy the futuristic mix.

A bird's-eye view of the Aspen FACE facility and its 12 rings.