Fundamental Science: The global climate depends on the future of the Amazon

We all know that the Amazon Rainforest has been the scene of accelerated deforestation in recent years. But not everyone is aware of the consequences of this devastation. The more the forest is deforested, the lower its natural ability to recover. We have reached such a point that research already suggests that the Amazon is not far from reaching an alternative state of equilibrium that points to the savannization of the biome, with less vegetation and even poorer soils. This conversion to a new and irreversible deteriorated state — a moment that can be seen in the most varied ecological processes — is called tipping point (inflection point or critical point). Achieving such a state of degeneration would have global climate impacts, starting with CO_two In the atmosphere.

One of the main roles that the Amazon — erroneously recognized as the “lungs of the world” — plays in the global climate is its ability to store CO_two, and not to “filter” the global air. Through its slow and steady production of biomass, it stores carbon in its vegetation, soils and waters. This stock is directly associated with the functions of a healthy forest which, when in balance, has a balance between photosynthesis and respiration. It was the stability of this balance that ensured a slow growth of biomass in the region over the last two million years.

Since the Industrial Revolution, human activities have released approximately 700 gigatons of CO_two in the atmosphere, of which around 180 are stored in the Amazon — half in the biomass, half in the soil. This figure means that, in a scenario of complete devastation, the Amazon alone would dump into the atmosphere an amount of CO^­_two equivalent to 25% of all human contribution accumulated to date. In other words, the concentration of CO_two in the atmosphere would suffer a 20% increase (85 parts per million) and an equivalent warming of 0.5°C in the global average temperature.

How close are we to this degraded state? A review that I and 18 other scientists published in Science regarding the speed of impacts in the Amazon found that human advances in the region are hundreds to thousands of times faster than their recovery by natural phenomena. Geological processes and formation of rich ecosystems, as well as the construction of a high biodiversity act on time scales much longer than decades: they take from thousands to tens of millions of years. On the other hand, by 2019, 14% of the Amazon had been converted into fields for agriculture, and parts of the region no longer store carbon, on the contrary: they release more carbon than they rescue.

Just as the geological history of the region has been dynamic, the Amazon Rainforest itself has also undergone changes over the last 60 million years. Their species richness and size have fluctuated over the past tens of millions of years as global climate changes, the evolutionary history of the South American continent dictated by plate tectonics, and the uplift of the Andes. There is, however, no history of ecological and climatic changes that can match the speed of changes we observe today and which are led by human beings.

The imbalance between speeds is alarming, because despite occupying 0.5% of the entire Earth’s surface (including oceans), the Amazon is a crucial entity for the planet’s climate stability. It not only reacts to global changes, but also plays a regulatory role through its biomass, its wetlands and its soils. The problem, however, is that its regulatory capacity is increasingly reduced.

Each component of the region — its rivers, wetlands, uplands, mountains, plains, plateaus and plateaus — makes up the pieces of a complex ecological gear interconnected with each other and with the soils, biota and flora. Deforestation, in addition to its immediate impact, has long-lasting consequences — it is as if we jammed the gears. It is this aspect that generates the alarm, because, once the tipping point, the interconnection between geological, biological, ecological and climatic processes would lead to degradation on its own.

With increasingly rapid biomass losses, forests release their carbon into the atmosphere. The scarcity of vegetation also causes an increase in temperatures in the area and, therefore, greater vulnerability and incidence of droughts and fires. As a consequence, the volume of water recycled by evapotranspiration is altered, which causes changes in climate regimes — more intense storms that will eventually affect the volume of water in rivers and the river discharge of the system as a whole. Associated with these consequences, there is the degradation of the soil which, without its vegetation cover, becomes vulnerable to erosion by intensified storms and which result in the transport and removal of nutrients, losing their life-sustaining properties. With deteriorated soils, the forest’s ability to recover dissipates, feeding back the cycle. Presenting a more fragile ecosystem, the biota also suffers and loses biodiversity due to environmental stresses. The ripple effect takes place.

Forests impacted by human activities already have higher mortality rates, more degenerated soils, less vegetation cover, lower humidity and higher temperatures, factors that contribute to the forest not being stable enough to grow over time. As deforestation advances, it will no longer be able to store carbon and will become predominantly a source of CO_two.

National and global conservation policies can prevent irreversible damage, slowing climate change, preserving global biodiversity and protecting indigenous peoples and their knowledge. To conserve the Amazon is to contain the global climate crisis.

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Pedro Val is a geologist and professor at Queens College, City University of New York.

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