With every passing day, it becomes increasingly urgent that the world do more to reduce its carbon emissions. The good news is that we’ve not yet exhausted the low-hanging fruits of this effort—especially those found in tropical forests.

Forests are good carbon sinks, which means they locks away more CO2 in trees than they emits. Tropical forests, with their dense greenery, are particularly good at this. For those living around these forests, however, cutting down trees often makes for a decent living: there’s timber to sell, and deforestation opens up land for all sorts of uses. No surprises that, in many parts of the world, it’s hard to preserve forests.

A way around the problem is to pay the people in such areas to not cut down trees. You’d have to give them enough to cover the money they would otherwise make, which means it’s not financially feasible in rich areas. But in poor ones, the economics appear to work out.

A group of researchers from the US, the Netherlands, and Belgium recently tested out the scheme in a forested region of Uganda. They randomly divided 121 villages in the area into two groups. Workers from the local charity Chimpanzee Sanctuary and Wildlife Conservation Trust went to the villages in one of the groups and offered individual landowners $28 in exchange for a guarantee that they’d leave one hectare of forest uncut. After spot checks to ensure that they had lived up to the promise of not cutting trees in their designated patch of the land, those who had agreed to the offer received the money.The researchers also double checked with the help of satellite images to ensure people weren’t cheating. The workers and researchers did not contact the villages in the second group.

The results, published in Science, show that the business-as-usual villages lost 9.1% of their tree cover in the study period, while those that agreed to the contract lost just 4.2%. The researchers calculate that across all the villages they paid, more than 180 metric tons of carbon emissions were prevented per participating landowner at a cost of $0.46 per metric ton. That’s 10 to 20 times cheaper than the carbon offsets you can purchase from commercial services like Cool Effect or Carbon Fund.

There are many ways forests store carbon. Primarily, they do it by converting carbon dioxide into nutrients for trees. Some of these nutrients end up in barks and roots, where they stay locked until the tree is cut. Others end up in leaves, which get buried in soil and keep the carbon locked. When trees are cut, the carbon is released through burning it for fuel, natural degradation, and through the release of carbon in the soil around the tree.

But even if the villagers who participated in the study eventually chop down the trees they’d avoided cutting, the delayed release of carbon would justify the cost. As a greenhouse gas, carbon dioxide absorbs and stores the heat from the sun. Thus, its impact on climate change is calculated not just by the absolute amount of CO2 in the atmosphere at any given time but by the cumulative amount of the heat absorbed by the gas. This number, meant to measure the negative effects of increased global warming due to emissions, is also called the social cost of carbon.

In the Uganda study, the researchers calculated that the value they derived from delaying the release of carbon was about 2.4 times the cost they paid to keep that carbon stored for that bit longer.

Such “payments-for-ecosystem-services” schemes have been applied in the past in countries like Mexico and Bolivia, but their effectiveness wasn’t clear. This latest study—a randomized, controlled trial—is excellent proof that we still have at least one cheap way to mitigate climate change, as long as we apply it properly.

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