Tropical rainforests cover roughly 18% of Earth’s land area, yet they hold an outsized influence over the planet’s climate, biodiversity, and even modern medicine. Their importance goes far beyond being “the lungs of the Earth,” a popular phrase that, as it turns out, oversimplifies the science. Here’s what tropical rainforests actually do and why losing them would reshape life on the planet.
They Store Enormous Amounts of Carbon
The single most critical function of tropical rainforests is regulating Earth’s climate by pulling carbon dioxide out of the atmosphere. Globally, forests absorb nearly 16 billion metric tons of CO₂ per year and currently hold about 861 gigatons of carbon in their branches, leaves, roots, and soils. Tropical rainforests account for a disproportionate share of that storage because their dense vegetation and year-round growing season mean they’re constantly converting atmospheric carbon into biomass.
This matters because when rainforests are cleared or burned, all that stored carbon gets released back into the atmosphere, accelerating climate change rather than buffering it. The Amazon alone is already showing signs of stress. Previous studies suggest the Amazon could cross an irreversible tipping point if forest loss exceeds 40%, potentially transforming large stretches of rainforest into savanna. A 2024 analysis found that up to half of the Amazon could face unprecedented stress by 2050, pushing it closer to that threshold. Once a tipping point like this is crossed, the forest can no longer regenerate on its own, and the carbon it held for centuries enters the atmosphere permanently.
Home to Most of Earth’s Species
Tropical rainforests are the most biologically rich ecosystems on the planet. A study published in Frontiers in Ecology and the Environment found that tropical forests harbor 62% of global terrestrial vertebrate species, more than 21,000 species of mammals, birds, reptiles, and amphibians, all within that 18% land footprint. And that figure only counts vertebrates. Vascular plants and invertebrates (insects, spiders, worms) couldn’t be fully assessed due to limited data, meaning the true proportion of species dependent on tropical forests is almost certainly higher.
This concentration of life isn’t just interesting from a nature-documentary perspective. Ecosystems with higher biodiversity tend to be more resilient, meaning they recover faster from disturbances like drought or disease. They also provide more “ecosystem services,” the practical benefits humans get from nature, like pollination, pest control, and water filtration. When you lose a rainforest, you don’t just lose trees. You lose thousands of species and the ecological relationships between them, many of which scientists haven’t even catalogued yet.
A Major Source of Modern Medicine
About 25% of drugs used in modern medicine are derived from rainforest plants. That number is even more striking in specific categories: half of the anticancer drugs introduced since the 1940s are either natural products or their derivatives. Of the top 150 prescription drugs sold in the United States, 118 trace their origins to natural sources.
Some of the most well-known examples come directly from indigenous knowledge of rainforest plants. Quinine, still one of the most important treatments for malaria, was isolated from the bark of the cinchona tree in the tropical rainforests of the Andes. The Quechua people of South America had been using it as traditional medicine long before Western pharmacology identified it. Cortisone, an active ingredient in birth control pills, came from wild yams found in South American rainforests, where native communities had already recognized the plant’s medicinal properties. A treatment for glaucoma was developed from calabar beans found in the tropical forests of Africa.
In the last 25 years, 70% of new drugs introduced in the United States were derived from natural products, despite advances in synthetic chemistry and laboratory drug design. The implication is clear: rainforests contain chemical compounds that scientists still can’t replicate from scratch. Every hectare of rainforest lost potentially eliminates plant species whose medicinal properties were never studied.
The Oxygen Myth, Corrected
You’ve probably heard that the Amazon produces 20% of the world’s oxygen. The reality is more nuanced. Rainforest trees do produce enormous quantities of oxygen through photosynthesis, but the organisms living in and around those trees, primarily microbes and insects that decompose fallen leaves, dead roots, and other organic matter, consume nearly all of it. The net oxygen contribution of forests, and indeed all land plants, is very close to zero.
This doesn’t diminish the rainforest’s importance. It just means that the real reason to protect rainforests isn’t oxygen. It’s carbon storage, biodiversity, water cycling, and the medicinal compounds locked in their plants. The oxygen framing, while emotionally powerful, actually distracts from the stronger and more scientifically accurate arguments for conservation.
Water Cycling and Regional Rainfall
Tropical rainforests act as massive water pumps. Trees pull water from the soil through their roots and release it back into the atmosphere through their leaves, a process called transpiration. In the Amazon basin, this cycle is so powerful that the forest essentially generates its own rainfall. Moisture released by trees forms clouds that travel inland, delivering rain to agricultural regions hundreds or thousands of miles away.
When large sections of rainforest are cleared, this cycle weakens. Regions that depended on forest-generated rainfall begin to dry out, affecting farming, freshwater supplies, and the remaining forest itself. This creates a feedback loop: less forest means less rain, which stresses more forest, which leads to further loss. It’s one of the mechanisms that could push the Amazon toward its tipping point.
Livelihoods and Food Origins
Tropical rainforests are home to an estimated 300 million people worldwide, including hundreds of indigenous groups whose cultures, languages, and knowledge systems are tied directly to the forest. Beyond those who live in rainforests, billions of people depend on products that originated there. Coffee, chocolate, bananas, black pepper, vanilla, rubber, and many tropical fruits all trace their origins to rainforest ecosystems. Even if these crops are now grown on plantations elsewhere, the wild genetic diversity in rainforests remains essential for breeding disease-resistant varieties and developing new agricultural strains.
Tropical rainforests are not a single resource with a single benefit. They’re interlocking systems that regulate climate, sustain biodiversity, supply medicine, drive water cycles, and support human communities. Losing them doesn’t just mean losing trees. It means losing planetary infrastructure that took millions of years to develop and that no technology can replace.