Aerial view of many different trees in a field

The uncomfortable balance between biodiversity and carbon capture

Two of the most pressing environmental problems of the 21st Century – climate change and biodiversity loss – are even more strongly linked than generally realised, scientists from two United Nations panels concluded in a report issued in June. That’s a concern, because it means that efforts to solve climate change can have unintended impacts on biodiversity.

The linkage between the two problems is complex, with multiple ways in which climate change can affect biodiversity, and vice versa, says Hans-Otto Pörtner, an ecophysiologist at the Alfred Wegener Institute, Bremerhaven, Germany, and member of the Intergovernmental Panel on Climate Change (IPCC).

For example, he says, natural ecosystems currently buffer climate change by absorbing more than 50% of worldwide emissions of planet-warming carbon dioxide.

About one million plant and animal species are threatened with extinction.

Without that, climate change would be much worse than it already is. But natural ecosystems can only help if they are healthy and diverse.

That’s where the other UN panel – the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) – enters the picture. In a 2019 “global assessment”, that panel found that about one million plant and animal species are threatened with extinction, eroding what IPBES’s then-chair, environmental scientist Sir Robert Watson, called “the very foundations of our economies, livelihoods, food security, health, and quality of life”.

Some of this is due to long-standing problems like habitat destruction, overfishing, pollution, and invasive species that hitchhike rides on ships, planes, produce, or even hiking boots, to wreak havoc in ecosystems unprepared for them – much like rabbits in Australia.

But climate change also plays a role, which is why the two organisations teamed up for their new, first of its kind, joint report, looking to assess how climate change and biodiversity can play off each other to create a vicious, downward spiral.

One problem, says Pörtner, is that the ability of many species to grow and sequester carbon is strongly dependent on temperate conditions. Even if these species don’t go extinct from global warming, their growth and ability to remove carbon dioxide from the air can be impeded. For example, a heat or drought-affected forest isn’t going to do as much as a healthy one to pull carbon dioxide out of the air, even if the trees don’t die or burn up in bushfires.

Nor is removing carbon dioxide from the air the only way ecosystems can mitigate the effects of climate change. Healthy mangrove forests along tropical coastlines, for example, can help shield coastal communities from the brunt of rising seas or severe storms, says Pamela McElwee, an interdisciplinary environmental scientist at Rutgers University, New Jersey, who works with the IPBES. Mangrove forests are also important because they can sequester four times more carbon per hectare than tropical forests, adds another member of the IPCC-IPBES team, Yunne-Jai Shin, a marine scientist at IRD (the French National Research Institute for Sustainable Development).

Even if these species don’t go extinct from global warming, their growth and ability to remove carbon dioxide from the air can be impeded.

Generally speaking, finding ways to stave off global warming should be beneficial to ecosystems. After all, climate change is one of the things that’s stressing them, so mitigating it should be to their advantage.

But it’s not always that simple. Some climate-control measures can actually be ecologically counterproductive.

An example, Pörtner says, is a large-scale switch to biofuels in an effort to reduce the use of fossil fuels. That’s definitely a way to reduce carbon-dioxide emissions, but it comes at a price, because bioenergy crops are land intensive. “They require a large share of land and threaten biodiversity,” Pörtner says.

And “large” means millions of hectares. “It’s equivalent to two times the land area of the entire Indian subcontinent,” says Almut Arneth, a plant ecophysiologist with Karlsruhe Institute of Technology in Germany, who was also part of the IPCC-IPBES team. Given the fact that more than half of the Earth’s land is already used for food production, she says, putting that much more into bioenergy crops would put “enormous pressure” on remaining wildlands and be “fairly catastrophic” for biodiversity.

If all of this sounds a bit depressing, it’s simply the way the real world of conservation works, says James Boyd, an environmental economist with Resources for the Future, a nonpartisan think tank in Washington, DC, who was not part of the study team.

Some climate-control measures can be ecologically counterproductive.

When people think about environmental problems, he says, they tend to think in terms of “profits and consumption” and “the market economy versus nature”.

“But increasingly,” he says, “we’re seeing nature-versus-nature tradeoffs.”

Biofuels, he adds, are an extremely good example – not just in agriculture, but in forestry. “Forests are incredibly able to soak up carbon,” he says. “If we could convert some of that into energy and thereby displace fossil fuels, that is in one sense good for the environment. But you have to think what harvesting those trees means. You can affect water resources and species.”

Similar problems can accompany renewable energy development. Solar power and hydroelectric power are good for the climate, but unless they are done with small-scale single-family systems, that green energy still needs to get to the market. “You have to create the transmission system to get it to people,” Boyd says. “That means changing landscapes.”

A similar problem, says Arneth, is that windmills and solar panels require materials that have to be mined from somewhere, either on land or on the seabed. “This is destructive to ecosystems,” she says. “Particularly deep seafloor mining. There is great concern about the destruction of ecosystems we don’t know [much about].”

When it comes to approaching these problems holistically, some solutions are fairly simple. Planting a fast-growing monoculture of non-native trees might be an effective way of pulling carbon out of the air, says IPCC-IPBES team member Peter Smith, a climate researcher at the University of Aberdeen, UK, but it’s not going to be good for biodiversity. A mixed woodland, however, has no such problem. “It’s not a matter of what you do, but how it’s implemented,” he says.

When it comes to approaching these problems holistically, some solutions are fairly simple.

Other win-win measures can be found by focusing on farming and grazing, says Arneth. These, she says, are major sources of greenhouse gas emissions (especially when you include methane as well as carbon dioxide). But, she notes, “agriculture is [also] a major driver of biodiversity loss.”

That opens the door for measures that can simultaneously reduce agriculture’s carbon footprint and reduce its impact on biodiversity loss. Examples range from restoring degraded soils by building up their carbon content, to reducing the use of pesticides (which not only affect biodiversity, but require energy to produce).

The bottom line, says Paul Leadley, an ecology professor at Paris-Saclay University, France, is that we need to consider the ramifications of proposed solutions to the climate crisis to make sure they don’t have undesired knock-on effects.

Or, as Boyd puts it, natural systems, economies and societies are complex systems. “It’s amazing how much we’re trading off one objective against another,” he says. “With a lot of these issues it’s not a ‘yes’ or ‘no.’ It’s probably ‘yes … but’.”