Context – Tipping Points– Amazon Forest Collapse

1. Overview

Summary derived from Thresholds- Temperatures and Timeframes (from McKay et al, Science (2022):

Type – Multiple Reinforcing Feedbacks, State-Change Tipping Point
Threshold temperature rise (estimated) – + 3.5 degrees C (minimum – 2 degrees Celsius, maximum – 6 C).
Abrupt Change Potential – Yes (low confidence)
Reversibility – Irreversible over multiple decades (medium confidence)
–Time-frame, estimated, to reach tipping point is 100 years (minimum – 50 years, maximum, maximum – 200 years).

2. Mechanisms

Feedbacks –

Water Cycle – Rainforests as the name suggests, are forest areas of high rainfall but there is a critical dependency such that without that heavy rainfall the forest would not actually exist. But the forest ecosystem is also a feedback system as through photosynthesis it recycles water back into the atmosphere in a process known as transpiration. This transpiration combined with evaporation ‘the two processes together known as ‘evapotranspiration’, lifts huge volumes of water that fall back as rain thus self-sustaining the system– the Amazon is estimated to generate about half of its own rainfall. Any break in this cycle undermines the resilience and ultimately the existence of the forest .

As the Carbon Brief Tipping Points explainer indicates: ‘ either reducing the amount of rainfall or the amount of forest can shift the [regional] climate into a drier state that cannot support a rainforest…. There is only so much drying that the Amazon could tolerate before the rainforest would no longer be able to support itself’

So the reinforcing (positive) feedback results from a reduction in water delivered to the forest, which causes drought and forest die-back and further reduces the water cycle.

The following diagram illustrates from climatetippingpoints.info illustrates how the rainforest functions in a healthy state and how reductions in the water cycles can result in the loss of forest.

Deforestation — The second feedback element is caused by deforestation which comes in two main forms; wild fires and human caused forest clearance. As water feed to the forest reduces, drought induced forest fires increase in number and severity which can destroy thousands more hectares of forest in a year. The reduced forest cover and further diminishes the water recycling in a further spiral of the feedback.

The same dynamic is caused by forest clearance for agriculture purposes for beef and palm oil production , for mining and logging all on a massive scale. According to Rainforest Foundation US, 44.2 million acres of Brazil’s Amazon burned in 2024; that figure was up 66% compared to the previous year, which itself was up 35% on 2022 figures.

Tipping Points?

Forest Shift to Grassland –

According to World Wild Life in 2022, 17% of the Amazon has been already been lost and a further 17% has been weakened (‘degraded’) and therefore at increased risk of loss in the foreseeable future, especially combined with the drought conditions experienced in recent years.

As explained in the ClimateTippingPoints.info when enough trees are lost in key areas from drought, deforestation and wildfires the forest or large areas of it can shift state from a forest to a lower ecological, grassland (savannah) system.

Quantifying the destabilisation; Carlos Nobre has determined from other works and evidence that on its own, 4C of global warming would be the tipping point to degraded savannah lands in most of central, southern and eastern Amazon. However the combination of drought and the fragmenting effects of deforestation brings the tipping point down to about +3C but that much uncertainty remains.

While Nobre has indicated that a loss of 40% would result in the collapse of the self-sustaining Amazon forest system, other studies have reported that the combination of factors, the forest loss threshold for the Amazon collapse to Savannah could be in the region of 20-25%; dangerously close to the current reported figure of 17% loss.

Carbon Sink to Source –

It is estimated that the Amazon ecosystem alone stores between 150-200 billion tonnes of Carbon (GtC) which is equivalent to 550 – 734Gt CO2 or more than the remaining total global carbon budget for 1.5C warming and half the remaining budget for 2C warming.

The Amazon alone removed about 5-10% of yearly human emissions over the past few decades. However as the climate continues to warm, a thermal maximum for photosynthesis is reached. At higher temperatures, it was shown by Katharyn Duff and colleagues that while respiration rates continued to rise (releasing carbon dioxide) in parts of the Amazon, photosynthesis rates declined sharply resulting in the approach of tipping point whereby the forest stops being a carbon sink and converts to being a carbon source.

But as the Amazon has acted as a sink for Carbon when a healthy vibrant system it can also operate in the opposite direction when its vitality has been undermined. It has indeed recently been reported that the Amazon, the forest has converted to being a net Carbon source resulting from a combination of reducing photosynthesis rates, deforestation and drought, although that change is said to reversible.

3.Impacts

Carbon and Heating Feedbacks –

The following Climate Tipping Point article excerpt illustrates the potential carbon impacts at their worst:

‘If wide-scale dieback were to be triggered then far more CO₂ release could be locked in over the coming decades. The total Amazon carbon store is estimated to be 150-200 GtC (with ~70GtC in plants), with total dieback to savannah estimated to release 53-70 GtC and raise atmospheric CO₂ by 25-33 ppm, around 5 to 7 years worth of current human emissions. Along with biogeophysical feedbacks this CO₂ rise would be enough to cause an extra 0.1-0.2^oC of global warming over the next century, along with extra regional warming of 1-2^oC as the forest’s self-cooling ability is reduced’.

Whilst the tipping point may take many decades to occur, the heating that causes the reduced photosynthesis, drought and fires all contribute towards increasing the Amazon’s carbon release and driving further warming in a vicious multi-factored feedback.

Other Impacts –

But the global carbon contribution of reaching an Amazon tipping point is only one (though highly consequential) part of the account. A huge range of negative impacts from a die back or ultimate collapse of the Amazon would occur as outlined by the World Wildlife Fund below:

As the world’s largest tropical forest and river system, the Amazon is an unparalleled and complex biome:

People: 47 million people live in the Amazon region and depend upon it for their livelihoods. This includes 2.2 million Indigenous peoples from more than 500 different groups.

Biodiversity and wildlife: The Amazon is home to a stunning array of the world’s species: 9% of mammals; 14% of birds; 8% of amphibians; 13% of freshwater fish species; and 22% of vascular plant species. Many of these species are found nowhere else in the world, and scientists estimate there are places in the Amazon where up to 90% of the species are yet to be discovered.

Forests: Without its forests, the Amazon region would lose its biodiversity, release massive amounts of carbon, suffer soil erosion, and face hydrological and climatic devastation. Without its ecosystem services, local communities and people around the world would face a loss of livelihoods, well-being, and ecological stability.

Climate: The Amazon is a major carbon sink that regulates and helps stabilize the planet’s climate. Any loss or degradation of its forests means an increase in carbon emissions. Today, land conversion and fires in the region are already releasing some of that carbon into the atmosphere at record highs.

Food: The Amazon’s “flying rivers” transport moisture outside of the basin to the southern part of the continent, providing the necessary conditions for agriculture in Argentina, Paraguay, Uruguay, and southern Brazil. The health and vitality of the Amazon River basin are also fundamental locally for the millions of people who rely on its waterways for fish.

Freshwater: The Amazon is the largest free-flowing river in the world. Home to 20% of the freshwater discharged into the Earth’s oceans, the Amazon must stay free flowing and healthy. Its connectivity and water quality impact not only the river basin but also human health, food security, livelihoods, and the mangroves and surrounding wetlands the river passes on its way to the Atlantic Ocean.

Ancestral knowledge: People have lived in the Amazon for more than 12,000 years, making the region a rich repository of human history and ancestral culture.

The health of the Amazon has both local and far-reaching impacts. Losing the Amazon would drastically change the climate of South America, worsening food security, intensifying the climate crisis, and ultimately affecting the entire planet. The global climate emergency would accelerate, as keeping planetary warming below 1.5 degrees Celsius would be impossible.

Conclusions –

It is worth concluding with the balanced final conclusions of ClimateTippingpoint.info noting the uncertainty as well as the global significance of this complex and vulnerable key ecosystem with all its incredible totemic diversity of life, beauty and culture:

Together with the ongoing sink-to-source transition, triggering wide-scale Amazon dieback would make keeping to the Paris climate target of well under 2^oC much harder, and the more ambitious 1.5^oC target nigh on impossible. Given that deforestation has already reached ~17% in the Amazon and global warming has reached around ~1.2^oC, reducing global CO₂ emissions and halting rainforest degradation are paramount both for ensuring what remains of the Amazon can survive and to keep global warming as close to 1.5^oC as possible.

Even though Amazon dieback is uncertain, a tipping point likely not yet reached, and it would not cause a sudden climate catastrophe, this does not reduce the importance of the Amazon rainforest for the Earth. It still harbours huge ecological and cultural diversity and forms a critical part of the Earth system’s carbon and water cycles. That full dieback has not yet been reached and that degradation can still be halted and partially reversed makes this a critical window in which the Amazon’s fate has not yet been determined.

MCL – February 2025 (next update schedule: Spring 2028; more regular updates in the ‘Recent Posts and News Section’).

4. Recent Posts and News Articles

Climate Junction –

Updates – Amazon forest