Having trouble finding that last minute holiday present for someone? Perhaps you could buy them some biodiversity.

You might be wondering if I’ve sampled too much of my buddy’s legendary holiday eierlikör (look it up). After all, biodiversity isn’t a thing like the latest iPhone that can be easily quantified and is identical across the world. You might as well talk about getting someone a bag of peace.

And yet, more and more companies are trying to turn biodiversity into a commodity by selling “biodiversity credits.” One offers a token that they claim equals 50 years of carbon and biodiversity protection on a hectare of tropical rainforest. Another credit is billed as a way to buy a month’s worth of biodiversity protection on a chunk of the Amazon in Colombia. There are dozens of such ventures.

Whether those credits really do what is claimed, however, is another question. A group of prominent conservation scientists are warning that while they might seem like an attractive way to raise money for conservation or offset environmental damage, a credit could turn out to be the proverbial lump of coal in the Christmas stocking.

“It is phenomenally difficult to reduce something as complex as biodiversity to a single number, meaning there are many risks to developing a market that trades in nature,” says Hannah Wauchope, an ecologist at the University of Edinburgh and lead author of a recent paper scrutinizing these credits in Proceedings of the Royal Society B: Biological Sciences.

While the prospect of turning biodiversity into a credit might sound weird, anyone who follows conservation policy is probably familiar with work to put a price tag on an environmental good. Consider carbon credits, meant to represent a measurable amount of greenhouse gases that were either sucked from the atmosphere or kept from being emitted.

But the carbon market has also been dogged by uncertainty about whether these credits live up to their promises. Just last year, scientists reported in the journal Science that of 26 forest conservation projects selling carbon offsets, most didn’t have a significant effect on deforestation rates.

Making good on the claims contained in biodiversity credits could prove even trickier, warn Wauchope and her co-authors, who vetted more than 40 different credit programs. They point to a number of potential difficulties.

Unlike carbon credits, which are usually tied to a quantity of carbon or carbon dioxide, there is no single, agreed-upon unit to measure biodiversity. Is the amount of a forest left untouched an adequate representation of biodiversity, or should it also include some key species? If so, how do you decide which species? And if biodiversity can be reduced to a token, how does a token’s worth of biodiversity in a jungle equate to a token of biodiversity in a savannah?

Then there’s the challenge of monitoring changes in biodiversity to see whether these credits are really keeping their value on the ground. Ecosystems are notoriously messy and difficult to monitor.  Fluctuations in species populations can be hard to detect or to make sense of. There’s a risk that someone selling credits might be rewarded or punished for changes that are nothing more than random fluctuations or statistical flukes, what the authors describe as “commodifying noise.”

Another hurdle is proving that purchasing a credit really benefited biodiversity in a way that wouldn’t have happened if the credit hadn’t been sold. The conundrum, known as “additionality”, is critical to people having confidence that a credit had a measurable effect in the real world. Just because a credit brings more money to a conservation project doesn’t mean it brings results. It’s also possible that blocking logging in one place simply pushed it somewhere else.

The integrity of these credits is particularly important if a company or government buys them based on claims that they compensate for damage caused by another action, such as allowing a forest to be logged. If that credit turns out to be flawed, it’s helping to allow a net loss of biodiversity, one that might be overlooked based on the assumption that the credit is real.

“We can’t avoid all impacts of human activity on nature, so we need to be able to compensate for the damage that we cause to nature,” said E.J. Milner-Gulland, a conservation scientist at the University of Oxford who worked on the study. “Our review demonstrates how challenging it is to do this via a tradeable ‘unit of nature.’”

While credits have the potential to give a boost to biodiversity, it will take “unprecedentedly strict regulation,” says Wauchope. And there are enough uncertainties that they should be used to measure helpful contributions, rather than as a way to offset damage, she said.

So perhaps a biodiversity credit could be a stocking stuffer. But beware of overpromising how big that gift is.

Wauchope, et. al. “What is a unit of nature? Measurement challenges in the emerging biodiversity credit market.” Proceedings of the Royal Society B. Dec. 11, 2024.