The Amazon Rain Forest and Climate Change

• Earth and Its Climate
  • Introduction
  • Our Atmosphere
  • Climate and Weather
  • The Greenhouse Effect
  • Greenhouse Gases
  • The Carbon Cycle
• Evidence of Climate Change
  • Man-made Change
  • Temperatures
  • Oceans
  • Snow and Ice
  • Rain, Drought, Extreme Weather
  • Ecology
• Future Projections
  • A Quick Look
  • Warming
  • Oceans
  • Ocean Ecosystems
  • Terrestrial Ecosystems
  • Health
  • Economics
• Brazil, the Amazon, and Climate Change
  • Brazil’s CO₂ Emissions
  • Tropical Forests and CO₂
  • Deforestation
  • Fires and Weather
  • Other Consequences
  • Carbon Sequestration and REDD
• International Agreements
  • UNFCCC: Convention on Climate Change
  • Kyoto Protocol
  • Emission Reductions

Tropical Forests and CO₂

Together, the world’s tropical rainforests absorb about 1.8 billion metric tons of carbon annually, storing about one-quarter of the world’s greenhouse gas emissions in their wood and soil.

Map of the world’s tropical forests

Scientists estimate Amazonian trees contain the equivalent of 9-14 years of current global, annual human-induced carbon emissions. Trees absorb carbon from the air as carbon dioxide and use the sun's energy to make leaves, branches, trunks and roots through the process of photosynthesis. Part of this carbon also ends up in the soil. When a tree dies and decomposes naturally, fungi and bacteria slowly break down the rotten wood, releasing carbon dioxide. Most of the wood, twigs, and leaves in a deforested area will decompose in 10 years. If the area is reforested, these trees will take more than 100 years to absorb a similar amount of carbon.

The amount of carbon stored in the Amazon is enormous. Per unit area, forests hold 20 to 50 times more carbon in their wood, leaves, and soil than cleared land. And trees in the tropics store about 50% more carbon per hectare compared to northern forests. This means cutting tropical trees releases much more carbon than cutting trees in forests elsewhere.

But under some natural conditions—especially drought or high temperatures, tropical forests can become net emitters of carbon. A study of trees in over a hundred different plots across the Amazon during the 2005 drought found that many trees grew much more slowly or died. As a result, the Amazon then became a source of CO₂, rather than a sink that takes up excess CO₂.

Climate models hint that weather conditions (El Niño, for example) that promote drought in the Amazon may occur more frequently in the future. This makes preserving the forest now even more critical to the planet’s health since it is going to take years for humans to significantly reduce their dependence on fossil fuels.

Wildfires also emit lots of greenhouse gases, especially in drought-prone El Niño years. In the El Niño of 1997-1998, fires released 2.1 billion tons of carbon—about one-quarter of a year’s worth of human-induced global emissions. When climate change combines with El Niño events, there is less rain and consequently, higher probability of forest fires. Once the forest catches on fire, its vulnerability to new fires increases. Fires can also get out of control and burn fences, pastures, or crops. One study has conservatively estimated that fires in the Amazon cost an average of about 0.2% of the region’s GDP annually, but the true number could be as high as 10%.