The Amazon tipping point theory?

The Amazon tipping point theory postulates that another 2-10% deforestation could make the world’s largest tropical rainforest too dry to sustain itself. Thus the Amazon would turn into a savanna, releasing 80GT of carbon into the atmosphere, single-handedly inflating atmospheric CO2 by 40ppm (to well above the 450ppm limit for 2C warming). This matters as Amazon deforestation rates have already doubled under Jair Bolsonaro’s presidency. This note explores implications, including international tensions, divestments, prioritization in a Biden presidency, and consequences for other transition technologies.


Global deforestation remains the single largest contributor to CO2e-emissions induced by man’s activities, more than the emissions from all passenger cars; and destruction of nature remains the largest overall contributor, more than all of China (chart below). This note is about a particularly worrying feedback loop in the Amazon rainforest, which could single-handedly wipe out the world’s remaining CO2 budget, effectively negating the impact of all other climate policies globally.

What is the Amazon tipping point theory?

The Amazon rainforest currently covers 5.5M square kilometers, comprising the largest, contiguous tropical forest in the world. 50% is in Brazil, and the remainder is spread around Peru, Colombia and half-a-dozen other South American countries. It contains 20% of all the planet’s plant and animal species, including 40,000 plant species alone.

Deforestation of the Amazon has reached 15-17% of its original area overall, and around 19% in Brazil. 800,000 square kilometers has been lost to-date (a land area equivalent to 2x California; or all of France plus Germany). Brazil’s annual deforestation rates have averaged 20,000 square kilometers per year from 1990-2004 (the land area of New Jersey or Slovenia). But the rate slowed to a trough of 5,000 square kilometers in 2014 due to improving environmental policies.

Unfortunately, more recently, Brazil’s deforestation rate has re-doubled (chart below). Jair Bolsonaro’s Presidency began in January-2019, following campaign pledges to ease environmental and land use regulations (which require 80% of legal Amazon land holdings to remain uncleared). Violations of these regulations are now said to be going unpunished. Bans on planting sugarcane in the Amazon have been lifted. Bolsonaro has even repudiated data published by Brazil’s own government agencies showing deforestation rates rising and accused actor and environmentalist, Leonardo DiCaprio of starting wildfires!

This matters because of the hydrology of the Amazon. Water in the basin tends to move from East to West. Each molecule typically falls as rainfall six times. It is repeatedly taken up by trees, transpired back into the atmosphere, and precipitated back down to Earth. Over half of the rain falling in the Amazon has originated from trees in the Amazon. It is a self-sustaining feedback loop.

The Amazon Tipping Point theory predicts that below some critical level of forest cover, this self-sustaining feedback loop will break. Less rainforest means less transpiration. Less transpiration means less rainfall. Less rainfall means less rainforest. Specifically, converting each hectare of forest to cropland reduces regional precipitation by 0.5M liters/year.

After the tipping point it is feared that the basin will transition into a savanna or scrubland. 50-100% of the forest cover would die back.

Unfortunately, this is not a ‘fringe’ theory. Many different technical papers acknowledge and model the risk, although specific climate models are imprecise, and do not always agree on timings and magnitudes. For example, the Western Amazon, closer to the Andes, might retain more forests than the East and Central parts of the basin. Another uncertainty is the moderating impacts of fire, as dryer forests will be more flammable, and thus more susceptible to slash-and-burn clearances, while raging fires will also reach further.

When is the tipping point? Various technical papers have estimated that the Amazon tipping point occurs when 20-25% of the forest has been cleared. This is an additional 2-10% from today’s levels, equivalent to deforesting another 100-600k acres, which could happen within 2-30 years.

What carbon stock is at risk of being released?

A typical forest contains around 300T of carbon per hectare (chart below). Thus 5.5M square kilometers of the Amazon is expected to contain 165GT of carbon. About 40% of the carbon is usually stored in trees (estimated at 60-80GT in the Amazon) and 60% is stored in roots and soils, which degrades more slowly. Hence, if just half of the remaining Amazon disappears, this would slowly release c80GT of carbon into the atmosphere.

Each billion tons (GT) of carbon released into the atmosphere is equivalent to raising atmospheric CO2 by around 0.5ppm. Hence a 80GT carbon release from the Amazon would by itself raise atmospheric CO2 from 415ppm today to around 455ppm. This single change (notwithstanding the continued and unmitigated burning of fossil fuels) would tip the world above the 450ppm threshold needed to keep global warming to an estimated 2-degrees (climate model below).

Can the tipping point be averted?

The solution to Amazon tipping points is technically simple: stop burning down forests and start re-planting them. This does not require electrolysing water molecules into hydrogen, smoothing volatility in renewable-heavy grids, or developing next-generation batteries. It requires something much harder: international diplomacy.

Inflammatory statements? In September-2019, Bolsonaro defended his environmental policies in a speech at the UN General Assembly. International critics were accused of assaulting Brazil’s sovereignty. Brazil considers itself free to prioritize economic development over environment.

Forest for ransom? In the past, Western countries have actually paid Brazil to safeguard its rainforests, although this arrangement has now fallen apart. Specifically, the ‘Amazon Fund’ was created in 2008. It is managed by Brazil’s state-owned development bank, BNDES. $1.3bn has been donated to the fund, from Norway (94%), Germany (5%) and Petrobras (1%). But after taking office, Bolsonaro has packed the fund’s steering committee with members of his inner circle, and in May-2019, he started using the Fund to compensate land developers whose lands were confiscated for environmental violations. Hence Norway and Germany suspended fund payments.

Divestment and trade tensions? As Brazil’s stance on the Amazon has grown more confrontational, it is possible that decision-makers may distance themselves from the country. Global investment funds have threatened to divest. (Could Brazil even surpass the coal industry as the divestment movement’s whipping boy?). Multi-national corporations may also be more cautious around investing in the country (but probably at the margin). Finally, Amazon deforestation is said to endanger future trade deals.

The Biden Factor? President-elect Biden may also seek to influence the Amazon issue. Biden stated the world should collectively offer Brazil $20bn to stop Amazon deforestation and threaten economic consequences for refusing. An executive order re-entering the Paris Climate Agreement would also help the situation (Brazil had actually committed to restoring 12M hectares of native vegetation under the accord). It will be interesting to see how Biden balances climate-focused priorities in the US with this arguably more urgent issue abroad.

Crucial Conclusions? If the Amazon surpasses its tipping point, there would be no chance of limiting atmospheric CO2 to 450ppm or preventing a catastrophic loss of biodiversity. Diplomacy is difficult. But fortunately, decision-makers can take measures into their own hands. Our note below profiles tree-planting charities. This is the lowest-cost decarbonization option we have found in all of our research. It restores nature, including the Amazon. Ultimately, we have argued that restoring nature may the most practical route to achieving climate objectives, while ‘bursting the bubble’ of other transition technologies.