Planting trees should reduce the amount of CO₂  in the atmosphere right? Well, its not so easy as that. Trees also provide shade and prevent sunlight from reaching the ground that could reflect it back into space, cooling the plant, known as the albedo effect. That means sometimes it makes more sense to cut the trees down and expose the more reflective ground than allow a forest to grow up, according to a study published in Nature, Bloomberg reports. 

Tree-planting schemes have been widely promoted as low-cost, nature-based solutions to global warming. The new research suggests that the climate benefits of forests need to be more closely studied as forests are not a win-win, but a trade-off.

The study found that forests in certain regions could do more harm than good — not because of their carbon absorption potential, but because of their impact on the Earth’s reflectivity. In areas like snow-covered landscapes, bright soils and grasslands, trees may reduce the amount of sunlight reflected back into space. This could raise surface temperatures and, in some cases, negate or even outweigh the cooling benefits provided by the trees’ carbon storage.

The findings carry significant implications for the global carbon offset market, where forest projects generate credits that companies buy to claim reductions in their climate footprint. “Despite the potential for albedo to reduce or even negate the climate mitigation benefits of some forest carbon projects, calculating for the effect of albedo is not considered in any carbon-crediting protocols to date,” said Libby Blanchard, a research associate at the Wilkes Center for Climate Science & Policy at the University of Utah and a co-author of the study, as cited by Bloomberg.

The oversight is especially concerning given recent scrutiny of forest-based offsets. Past investigations have revealed instances of overstated emissions reductions, undermining confidence in the voluntary carbon market. “As currently configured, [forest-based carbon offset] programmes are not delivering much in the way of climate benefits,” Blanchard added.

This is not the first time researchers have questioned the net benefits of tree planting. A June study by the US Department of Agriculture Forest Service found that lower albedo offset roughly half of the non-soil carbon storage gains from trees. Other papers have shown that forest loss in some mountainous regions in the western US can actually result in net planetary cooling. A third group concluded that “changes in albedo brought about by tree planting offset or even negate the carbon removal benefits” in most regions.

The authors of the Nature study argue that offset projects should be prohibited in regions — such as some boreal forests or drylands — where warming from albedo loss exceeds the benefits of carbon capture. Alternatively, credit issuance could be scaled down to reflect the warming impact.

“Forests are not a one-size-fits-all solution,” said Natasha White of Bloomberg. “This research further complicates the already fraught debate over the credibility of forest carbon credits, which have faced criticism for years over questionable methodologies and exaggerated claims.”

The offset market’s credibility now faces yet another scientific challenge — one that may force a fundamental rethink of how nature-based climate solutions are evaluated.