The effects of deforestation

Deforestation makes local weather hotter and drier, fills the air with smoke, strips away soil, wipes out wildlife and harms human health. In the film Deforestation, the consequences appear on screen one card at a time: extreme weather, air pollution, floodings, desertification, soil erosion, biodiversity loss "and even human impacts". This page takes them in that order, with the evidence behind each one and how certain it is.

Extreme weather: hotter days and less rain

Forests work like a cooling and watering system. Tropical forests release water vapor through their leaves, which cools the land and shapes rainfall locally and regionally.¹² The UN climate panel (IPCC) has high confidence that changes in forest cover directly affect regional temperature, and that changes in land can affect temperature and rainfall hundreds of kilometers away. Land changes can also significantly alter how likely, intense and long-lasting heatwaves (high confidence) and heavy rainfall events (medium confidence) are.¹

The evidence from the tropics is now direct. A study of forest loss from 2003 to 2017 found reduced rainfall over deforested regions across the tropics. At a scale of 200 kilometers, every percentage point of forest lost cut rainfall by about 0.25 millimeters a month. The authors estimate that future deforestation in the Congo will reduce local rainfall by 8 to 10% by 2100.² Clearing also heats the ground: tropical deforestation from 2001 to 2020 exposed 345 million people to local warming, with population-weighted daytime land surface warming of 0.27 °C.³

Then there is the global effect. Net CO2 emissions from land use averaged about 5.0 billion tonnes a year in 2015–2024.⁴ The IPCC has found that net land-use emissions are mostly due to deforestation.¹ That carbon adds to global warming. The latest numbers are on our deforestation statistics page.

Air pollution: the smoke from clearing fires

In humid tropical forests, fire is not a natural event. It is almost always set by people,⁶ usually to clear land for farming, and drought lets it spread.⁷ The smoke travels far beyond the burning forest.

In 2015, fires in Indonesia, largely started by farmers producing palm oil and timber for pulp and paper, covered Indonesia, Malaysia and Singapore in haze. Researchers estimated that the smoke caused upwards of 100,000 deaths across the three countries.⁵ In 2025, fires likely set by people again drove much of Bolivia's primary forest loss.⁸ Fire's growing role in forest loss is tracked on our statistics page.

Floods and landslides: what forests can and cannot stop

Here the evidence needs care. Forests can reduce the runoff that causes local flooding, though how much depends heavily on soil depth, soil structure and how saturated the ground already is. A joint review by FAO and the Center for International Forestry Research found no scientific evidence linking large-scale flooding to deforestation.⁹ Clearing a forested hillside can raise the risk of local flooding, but the evidence does not support blaming major, basin-wide floods on deforestation.

Landslides are clearer. Tree cover stabilizes soil, and when forests are cleared from land at high risk of erosion, soil becomes less stable, washes into waterways more easily, and the risk of landslides rises.¹⁰ In the Kivu Rift in Central Africa, a study of 58 years of population and forest change found that landslide risk in the eastern Democratic Republic of the Congo is now twice as high as in neighboring Rwanda and Burundi, and that recent large-scale clearing of primary rainforest there has increased the risk.¹²

Desertification and soil erosion: when land stops working

Desertification

The IPCC defines desertification as land degradation in arid, semi-arid and dry sub-humid areas, caused by many factors including climate variations and human activities. In 2015, about 500 million people lived in areas that had experienced desertification between the 1980s and 2000s.¹ Deforestation and desertification are not the same thing: nearly 94% of deforestation happens in the tropics.⁶ They meet in drylands. The IPCC notes that desertification releases CO2 as vegetation cover declines, and that tree belts can reduce sand storms and wind erosion where water allows.¹

Soil erosion

Tree cover holds soil in place. As of 2010, 47% of the world's tree cover grew in areas at medium to high risk of erosion, and in 2025, 9.3 million hectares of tree cover were lost in those areas, 36% of all tree cover loss that year.¹⁰ On farmland, soil is lost far faster than it forms. The IPCC estimates that soil erosion from agricultural fields runs 10 to 20 times faster than soil formation with no tillage, and more than 100 times faster with conventional tillage.¹ Erosion adds silt to water, reduces reservoir capacity and drives up the cost of treating and supplying water.¹⁰

Biodiversity loss: emptying the forest

Forests are home to a huge share of life on land. They provide habitat for almost 5,000 amphibian species (80% of all known), close to 7,500 bird species (75%) and more than 3,700 mammal species (68%). Some 60% of all vascular plants grow in tropical forests.¹¹

The global biodiversity panel IPBES estimates that around 1 million animal and plant species are now threatened with extinction, and ranks changes in land and sea use as the biggest direct driver of nature's decline. Three-quarters of the land-based environment has been significantly altered by people.¹³ Primary forest matters most: even when forest grows back, it is unlikely to match the original's biodiversity value for decades or longer.⁷

Human impacts: heat, disease and forest peoples

Heat. A 2025 study estimated that local warming from tropical deforestation is associated with about 28,000 heat-related deaths a year (95% confidence interval: 23,610 to 33,560). In regions of forest loss, it could account for over one-third of all heat-related deaths linked to climate. Death rates are highest in Southeast Asia, at 8 to 11 per 100,000 people living in deforested areas.³

Disease. IPBES attributes more than 30% of emerging infectious diseases to land-use change, agricultural expansion and urbanization combined.¹⁴ Deforestation also increases the risk of malaria: in the Brazilian Amazon, a study of 795 municipalities from 2003 to 2015 found that a 10% increase in deforestation led to a 3.3% increase in malaria incidence.¹⁵

Forest peoples. Roughly 100 million people depend on the forests of the Congo Basin alone.⁸ FAO calls Indigenous and Tribal Peoples the "best guardians" of Latin America's forests: deforestation rates are significantly lower in Indigenous and Tribal territories where governments formally recognize collective land rights, and those territories hold about one-third of the carbon stored in the region's forests.¹⁶ What works to stop the damage is on our page about solutions to deforestation, and what drives it is on the causes of deforestation.

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