Jack Branning is a prosperous Mississippi businessman, with commercial interests stretching from Hattiesburg to Baton Rouge, Louisiana. He’s seen a lot of deals in his 89 years, but few were as curious as the one he was offered back in 2013.

That’s when a forester walked into his office in Vicksburg and inquired about 1,700 acres of former soybean fields he owned nearby. The man worked for GreenTrees LLC, a small company that says it combats climate change by reforesting thousands of acres of farmland along the lower Mississippi River. GreenTrees says it pays landowners to convert their croplands to forests, tallies the planet-warming carbon absorbed by those trees, and then sells credit for the carbon reductions to big corporations that want to offset their own greenhouse gas emissions.

GreenTrees couldn’t reforest Branning’s land, because he’d already planted trees there more than a decade earlier thanks to a government conservation program. But the forester said the land still qualified for carbon payments. In effect, GreenTrees was offering to pay Branning for doing something he’d already done — and then take credit for it.