Some environmental solutions are win-win solutions that help curb global warming and also protect biodiversity. But others approach a crisis at the expense of others. For example, growing trees on grasslands can destroy the flora and fauna of a rich ecosystem, even if the new trees ultimately take up carbon.

What to do?

Unless the world stops treating climate change and biodiversity collapse as separate issues, none of the issues can be effectively addressed, according to a report released Thursday by researchers from two leading international scientific bodies.

“These two topics are more closely intertwined than originally assumed,” says Hans-Otto Pörtner, co-chair of the scientific steering committee that prepared the report. They are also inextricably linked to human wellbeing. But global policies usually target one or the other, which leads to unintended consequences.

“If you look at just one angle, you miss a lot of things,” says Yunne-Jai Shin, marine biologist at the French National Research Institute for Sustainable Development and co-author of the report. “Every action counts”

For years, a group of scientists and politicians has studied the climate crisis and tried to combat it, warning the world of the dangers posed by greenhouse gases that have been building up in the atmosphere since the industrial revolution. The main culprit: the burning of fossil fuels.

Another group has studied and tried to address the biodiversity crisis, warning of extinction and the collapse of the ecosystem. The main culprits: habitat loss through agriculture and overfishing at sea.

The two groups have largely operated in their own silos. But their themes are connected by something elementary, literally: carbon itself.

The same element that traps carbon dioxide, methane, and soot is also a fundamental building block of nature. It helps form the tissues of plants and animals on earth. It is stored in forests, wetlands, grasslands, and on the ocean floor. In fact, land and water ecosystems already store half of man-made emissions.

Another link between climate and biodiversity: Humans created emergencies on both fronts by using the planet’s resources in unsustainable ways.

Over the past few decades, the climate crisis has largely overshadowed the biodiversity crisis, perhaps because its threat seemed even worse. But the balance can shift. Scientists warn that the decline in biodiversity can lead to the collapse of the ecosystem, threatening the food and water supplies of humankind.

“Climate change of four or five degrees is an existential threat to humans, hardly imaginable,” says Paul Leadley, one of the authors and ecologist at the University of Paris-Saclay.

And he continued, “If we lose a really large part of the species on earth, it is an existential threat.”

Companies and countries are increasingly turning to nature to offset their emissions, for example by planting trees to absorb carbon. But the science is clear: nature can’t store enough carbon to keep emitting greenhouse gases at our current rate.

“Emission reductions, emission reductions and emission reductions have a clear first priority,” said Dr. Porter.

Just last month, the world’s leading energy agency announced that nations must stop approving new coal, oil and gas projects immediately if the world is to avoid the worst effects of global warming.

To make matters worse, some measures that are used or proposed to combat climate change could destroy biodiversity.

“Some people are selling this message that if we cover the whole planet with trees that will solve the climate problem,” said Dr. Leadley. “This is the wrong message on many levels.”

In Brazil, parts of the Cerrado, a species-rich savannah that stores large amounts of carbon, have been planted with monocultures of eucalyptus and pine to meet a global reforestation goal. The result, researchers have written separately, is an “impending ecological catastrophe” because it is destroying the indigenous ecosystem and the livelihoods of local communities, including the indigenous population.

Europe once hoped to be the world leader in biofuels until it realized they were leading to deforestation and increased food prices. Another type of bioenergy, wood pellets, is currently booming in the southeastern United States, despite concerns about pollution and biodiversity loss.

Climate interventions tend to harm biodiversity more than the other way around, and some compromises have to be made, the authors write. Solar parks, for example, eat up the habitat of wild animals, which is a problem especially for places with threatened species. Most importantly, they generate clean energy.

The report highlights ways to mitigate the damage to biodiversity, for example by grazing livestock in the area, improving carbon soil supplies and avoiding intact habitats. Pollinator gardens on solar farms can help feed insects and birds. While wind farms can injure migratory birds, the authors find that modern turbines cause much less damage.

By protecting and restoring nature, the report says, we can protect biodiversity, limit warming, improve human well-being and even find shelter from the effects of climate change such as increased floods and storms.

For example, in Senegal’s Casamance region, local communities have restored mangroves and implemented sustainable fishing measures, improved their catch, brought back dolphins and 20 species of fish, stored carbon and protected their coastline, said Pamela McElwee, an environmental anthropologist at Rutgers University who was one of the authors.

“Mangroves are a very special kind of ecosystem,” she said, “in that they do everything for people.”

Mangroves themselves are vulnerable to climate change, but Dr. McElwee said they seem less threatened than previously thought as the recovery efforts are working.

In the Hindu Kush mountains of South Asia, a project has preserved an area the size of Belgium, restored high-altitude forests and grazing land, and protected endangered snow leopards and musk deer, the report said, while keeping carbon out of the atmosphere. The 1.3 million people who live there, between Nepal, India and the Tibet Autonomous Region in China, have experienced higher household incomes through tourism and sustainable agriculture.

Urban areas can also make their contribution with native trees, green spaces and coastal ecosystems, according to the researchers.

The report was the first collaboration between the Intergovernmental Panel on Climate Change and the Intergovernmental Platform on Science Policy on Biodiversity and Ecosystem Services.

John P. Holdren, an environmental scientist at Harvard University and a former White House science advisor who was not involved in the report, called it “a must-see for our time.”

Brad Plumer contributed to the coverage.