Human impacts outpace natural processes in the Amazon

Abstract

Amazonian environments are being degraded by modern industrial and agricultural activities at a pace far above anything previously known, imperiling its vast biodiversity reserves and globally important ecosystem services. The most substantial threats come from regional deforestation, because of export market demands, and global climate change. The Amazon is currently perched to transition rapidly from a largely forested to a nonforested landscape. These changes are happening much too rapidly for Amazonian species, peoples, and ecosystems to respond adaptively. Policies to prevent the worst outcomes are known and must be enacted immediately. We now need political will and leadership to act on this information. To fail the Amazon is to fail the biosphere, and we fail to act at our peril.

Losing the Amazon

The Amazon rainforest is a biodiversity hotspot under threat from ongoing land conversion and climate change. Two Analytical Reviews in this issue synthesize data on forest loss and degradation in the Amazon basin, providing a clearer picture of its current status and future prospects. Albert et al . reviewed the drivers of change in the Amazon and show that anthropogenic changes are occurring much faster than naturally occurring environmental changes of the past. Although deforestation has been widely documented in the Amazon, degradation is also having major impacts on biodiversity and carbon storage. Lapola et al . synthesized the drivers and outcomes of Amazon forest degradation from timber extraction and habitat fragmentation, fires, and drought. —BEL

Abstract

Two Reviews spotlight the threats of ongoing deforestation and degradation in the Amazon.

Abstract

BACKGROUND

The Amazon is a critical component of the Earth climate system whose fate is embedded within that of the larger planetary emergency. The Amazon is the most species-rich subcontinental-scale ecosystem and is home to more than 10% of all named plant and vertebrate species, concentrated into just 0.5% of Earth’s surface area. The Amazon rainforest is also a critical component of the Earth climate system, contributing about 16% of all terrestrial photosynthetic productivity and strongly regulating global carbon and water cycles.

Amazonian ecosystems are being rapidly degraded by human industrial activities. A cumulative total of 17% of the original forest have already been cleared, and 14% replaced, by agricultural land use. After millions of years serving as an immense global carbon pool, under further warming the Amazon rainforest is predicted to become a net carbon source to the atmosphere. Some regions have already made the transition, with forest respiration and burning outpacing forest photosynthesis.

ADVANCES

In this Review, we compare rates of anthropogenic and natural environmental changes in the Amazon and South America and in the larger Earth system. We focus on deforestation and carbon cycles because of their critical roles on the Amazon and Earth systems. Data for South America were compiled for the Science Panel for the Amazon (SPA) Assessment Report, which details the many dimensions of the Amazon as a regional entity of the Earth system. The SPA report, coauthored by 240 scientists from 20 countries, documents epoch-scale transformations in Amazonian biodiversity, ecosystem function, and cultural diversity.

We found that rates of anthropogenic processes that affect Amazonian ecosystems are up to hundreds to thousands of times faster than other natural climatic and geological phenomena. These anthropogenic changes reach the scale of millions of square kilometers within just decades to centuries, as compared with millions to tens of millions of years for evolutionary, climatic, and geological processes. The main drivers of Amazonian habitat destruction and degradation are land-use changes (such as land clearing, wildfires, and soil erosion), water-use changes (such as damming and fragmenting rivers and increased sedimentation from deforestation), and aridification from global climate change. Additional important threats come from overhunting and overfishing, introduction of invasive exotic species, and pollution from the mining of minerals and hydrocarbons.

OUTLOOK

Given the outsized role of the Amazon in our planetary hydrological cycle, large-scale deforestation of this region is expected to push the whole Earth system across a critical threshold to a qualitatively different global climate regime. Quite aside from biodiversity losses, such a transformation will have multifarious and catastrophic consequences for human welfare, including widespread water and food insecurity that will lead to mass migrations and political instability. The key message is that Amazonian environments are being degraded by human industrial activities at a pace far above anything previously known, imperiling its vast biodiversity reserves and globally important ecosystem services.

The Amazon is now perched to transition rapidly from a largely forested to a nonforested landscape, and the changes are happening much too rapidly for Amazonian species, peoples, and ecosystems to respond adaptively. Policies to prevent the worst outcomes are known and must be enacted immediately. We now need political will and leadership to act on this information. To fail the Amazon is to fail the biosphere, and we fail to act at our peril.