There is no single silver bullet, like planting a trillion trees, to stop what scientists have identified as the twin threats of extreme climate disruption and biodiversity loss, but new research published today in the journal Nature shows that a holistic, global approach to healing ecosystems would be a big step in the right direction.
The study identifies restoration opportunities for forests, wetlands and grasslands that have been converted to farming or grazing areas, which degrades their value as habitat for threatened species, as well as their ability to absorb and store greenhouse gases. Many previous studies of nature-based climate solutions, including the massive tree-planting schemes, have focused more on individual types of ecosystems.
Protecting 30 percent of the priority areas identified by the new study could save the majority of mammals, amphibians and birds that are dying out and would soak up about 465 billion tons of carbon dioxide, equal to nearly half of the CO2 that has built up in the atmosphere since the start of the industrial age.
But such a restoration plan isn't a substitute for cutting greenhouse gas emissions, which is still the highest priority for limiting global warming, and the CO2-reducing climate benefits from healing ecosystems aren't immediate—they would accrue over many decades to come, said co-author Thomas Brooks, chief scientist for the International Union for the Conservation of Nature.
"It's really important to be honest, not to kid ourselves that there are perfect solutions to address all the challenges," he said. "We show that ecosystem restoration targeted in the right places can deliver enormous benefits to biodiversity and climate."
Restoration helps tackle global warming because healthy, natural ecosystems store huge volumes of carbon. When they are destroyed, the carbon goes into the atmosphere, so stopping ongoing ecosystem degradation is the first thing, he added.
"But it's really important that we not see the door as having been closed where conversion has already taken place," he said. "We can support the regeneration and regrowth of ecosystems, and in doing so, that extracts carbon from the atmosphere. It is an opportunity that we have."
Global Scale Solutions Needed
The study concluded that comprehensive restoration can be 13 times more cost-effective when it takes place in the highest priority locations, as opposed to an opportunistic, shotgun approach.
Lead author Bernardo Strassburg, director of the International Institute for Sustainability in Rio de Janeiro, said the study is one of the first to focus on the potential benefits of restoring both forest and non-forest ecosystems on a global scale. Reviving forests is critical for mitigating global warming and protecting biodiversity, but other ecosystems also have a massive role to play, he said.
The researchers mapped 10.8 million square miles of forest, grass, shrub and wetland ecosystems worldwide that have been converted to farmland and evaluated them based on their value as habitat for threatened species, their carbon storage potential and the cost of restoration.
Wetlands and forests are most important for biodiversity and mitigating climate change, but arid ecosystems and grasslands are desirable targets for restoration when the goal is to minimize costs. Converted areas within relatively intact tropical forests are among the highest priorities for the mitigation of climate change, while South American and African shrublands are priorities for protection of biodiversity.
"It is a very significant study, the first covering multiple ecosystems and multiple objectives, and timely, with the United Nations decade of ecosystem restoration starting in 2021," said Ana Rodrigues, a conservation ecologist with the Center for Evolutionary and Functional Ecology in France, who was not involved in the study.
The current global focus on reducing emissions from fossil fuel burning is justified, but that shouldn't detract from examining other aspects of the climate crisis, she said.
"I think people sometimes underestimate how much of climate change is due to land use, like the burning of the Amazon and the conversion loss of forests to agriculture," she said. "This study is complementary to the goal of avoiding more destruction. It set priorities for restoration."
The global mapping shows how much overlap there is between areas that are important for both biodiversity and climate protection, she added, which means global warming can't be fully addressed without simultaneously tackling biodiversity loss.
Farmland Can Be Restored Without Cutting Food Supplies
The researchers also addressed the question of how to make sure that ecosystem restoration doesn't diminish food production. They found that more than half of the areas that have been converted to crop or grazing lands could be restored as natural ecosystems without cutting food supplies.
The key is to intensify food production in the remaining areas in a sustainable way, along with reducing waste and shifting away from meat and dairy production, which require vast amounts of land and produce a disproportionately high amount of greenhouse gases.
The new study also acknowledges that ecosystem restoration has to consider the needs of people living in those areas. It shows, Rodrigues said, "what can be done without taking away agricultural productivity. The people that are there need to live, they need to eat."
Healthy, functioning ecosystems are much better at storing carbon than degraded lands, and biodiversity is at the foundation of what makes ecosystems function, said coauthor Robin Chazdon, an evolutionary biologist with the University of the Sunshine Coast in Australia.
The study's global scope is valuable because climate change and biodiversity loss are global problems, best addressed by collaborative international solutions, she said. These massive challenges require "transformative thinking, and the study points out the value of thinking about managing ecosystems at the planetary scale," she said.
And even if the climate benefits of ecosystem restoration aren't as immediate as shutting down coal plants, Chazdon said they are still important on a time scale that matters to the goals of the Paris agreement.
In tropical forests, which she studies most closely, about half of the above-ground carbon-storing biomass can be recovered in about 20 years after disruption. On average across tropical forests, ecosystem functions return in full after about 70 years. For grasslands and shrublands, the time scale is much shorter.
But in the end, "the study is just a map, a motivator," she added. "To really make any of this happen, we need political, economic and cultural change."