Understanding the Amazon Tipping Point

Why Preserving The Amazon May Be The Most Important Strategy To Fight Climate Change.

Anyone with a passing familiarity with climate change knows that scientists and activists are especially concerned about the Amazon Rainforest. Reaching the so-called ‘Amazon tipping point’ could devastate the Amazon and affect all ecosystems worldwide.

But what exactly does an ecological ‘tipping point’ mean? Can a change in the Amazon affect the entire Earth? And what does Amazon deforestation have to do with climate change in Europe or Australia?

Luckily, Dr. PM and I were able to work for the Amazon cause for a year, and we dedicated a good part of our work to communicating the peer-reviewed literature to public stakeholders worldwide. We want to share some of what we learned with you here.

How is Amazon precipitation created?

To understand the Amazon tipping point, we must first understand how the Amazon climate works.

Before the 1970s, there was a misconception that vegetation was just the result of local climate and that vegetation didn’t affect climate. Rather than something that had been concluded experimentally, there wasn’t a method available that would allow scientists to test whether this assumption was true.

Enter isotope science: a new emergent methodology that allowed the design of new experiments to shed light on this and many other issues. In the 1970s, Brazilian Scientist Dr Eneas Salati and his team proved the popular misconception wrong using isotopes.

How does isotope science work?

Elements in the periodic table, such as oxygen, always have the same number of protons in their nucleus. The number of protons is what determines what element they are. However, their number of neutrons can change.

Regarding oxygen, we have two common versions with different numbers of neutrons: oxygen-18 and oxygen-16. Oxygen-16 is the most common, and because it has fewer neutrons, it’s the ‘lighter’ oxygen. On the other hand, oxygen-18 is a rare form of oxygen with two extra neutrons in its nucleus compared to the more common oxygen-16. Therefore, oxygen-18 is the ‘heavy’ oxygen.

Scientists study oxygen-18 in water molecules and examine the ratio of oxygen-18 to oxygen-16. This ratio can tell them a lot about the history of the water, such as where it came from and how it has moved through different parts of the environment. By studying the isotopes in water, scientists can learn about past climate patterns, track the movement of water through different ecosystems, and even understand the chemistry of ancient oceans.

Using isotopes to understand precipitation patterns

Salati and his team collected rainwater samples across the Amazon and found that about 50% of the Amazon rainfall is generated by the Amazon itself. How so?

Most air circulation goes from the East, on the Atlantic coast of Brazil, to the West, in the Amazonian Forests of Colombia, Peru, and Ecuador, where the high elevation of the Andes Mountains forces the clouds to rise and cool. This generates the extensive precipitation that has created the Amazon Rainforest over millions of years.

However, the process isn’t unidirectional. Air masses, full of clouds created from the evaporation of Atlantic ocean waters, travel to the West in South America. During this transcontinental trip, the ratio of oxygen-18 to oxygen-16 in water vapor changes. Evaporated water tends to be rich in oxygen-18, but because water molecules with heavy oxygen-18 isotopes condense more quickly than normal water molecules, air becomes progressively depleted in oxygen-18 as it travels.

Plants absorb this oxygen-18-rich water through their root system. Therefore, the water that transpires from their leaves and evaporates back into the water vapor (clouds) system is also enriched with oxygen-18.

Salati and his team noticed that the water molecules in the rainwater samples collected from western areas contained more oxygen-18 than expected if water vapor had traveled across the continent after evaporating in the Atlantic Ocean only while losing more oxygen-18. This meant these water molecules had fallen as rain and re-evaporated along the way from rainforest vegetation, enriching the clouds with oxygen-18 again. Therefore, plants were responsible for most of the Amazon’s Rainfall.

Water wasn’t moving directionally into the system but circularly within the system. Approximately 50–80% of the Amazon’s rainfall is recycled through evapotranspiration. See the figure below.

The problem

Considering what we’ve been talking about, Amazon vegetation and forests in the West depend on the plant transpiration of forests in the East. That’s where their rainwater comes from. Breaking this cycle would deplete these forests from the necessary rainwater to sustain their ecosystem’s functioning.

The more areas are deforested, the less evapotranspiration. The less evapotranspiration, the less rainfall. And with less rainfall, rainforests die out. They need water to grow and maintain their biodiversity. As these forests die from drought, they also stop evapotranspiration, which leads to more deforestation… you get the picture.

Amazon rainforests have started dying from East to West because of this vicious cycle.

The tipping point

Following this chain of events, we may reach a point when Amazon’s evapotranspiration won’t be enough to sustain its healthy forests. The chain effects will unavoidably end with most of the basin turning into a dry savannah.

Models have estimated this will happen when deforestation reaches 20–25% of the Amazon forests. The good news? We are not there yet. The bad news? We are at 17% already.

Recent research has highlighted how the Amazon Rainforest already shows signs of reduced resilience. That is, Amazon ecosystems and carbon and water cycles are having a harder time recovering from normal natural events, such as localized fires or droughts. These used to be overcome more easily due to stronger relationships between all the elements at play. These relationships are now breaking.

How does this affect us globally?

Water Cycles

Reaching the Amazon tipping point would have devastating effects worldwide. We mentioned how the Amazon creates precipitation from vegetation transpiration. It is estimated that trees in the Amazon rainforest release around 20 billion tonnes of water into the atmosphere daily.

However, not all Amazon-created clouds stay in the Amazon. Some of these escape the system, influencing precipitation patterns as far away as the Western US. If no forest exists, Atlantic rainwater will be lost to dry soils, never returning to the water cycle.

Moreover, the Amazon River, the largest river system in the world, receives its water from these water cycles. Once it reaches the Atlantic Ocean, it discharges approximately 209,000 cubic meters of water per second into the Atlantic Ocean. The Amazon contributes ~17% of global river freshwater input to the ocean. This water has a tremendous impact on ocean currents and global water circulation.

Therefore, the loss or degradation of the Amazon rainforest by deforestation poses a significant risk to the water cycle, potentially disrupting rainfall patterns, altering regional climates, and exacerbating the impacts of climate change.

Carbon sequestration

Trees capture atmospheric CO2 to grow. But if we overdo deforestation and forests start dying out from lack of water, they will stop capturing CO2, speeding up the pace of global climate change and greenhouse gas emissions.

Recent studies document how some areas in the Amazon have already reversed their carbon sequestration role to turn from a carbon sink to a carbon source. The cumulative effects of climate change, forest fires, and deforestation may result in Brazil losing up to 11 million hectares of agricultural land by the 2030s. We can’t even begin to imagine the devastating effects that this could have on global food security.

Wrapping up

Losing the Amazon Rainforest as we know it could have devastating effects worldwide, from changes in precipitation regimes to increased carbon emissions and biodiversity loss.

Suppose we want to prevent the cascading effects that deforestation could have on Amazon ecosystems. In that case, we must take a holistic approach, such as improved sustainable economies that keep deforestation below 20%. Failing to do so could have unprecedented consequences for modern humans. As Thomas E. Lovejoy and Carlos Nobre wrote, “There is no point in discovering the precise tipping point by tipping it.”