We wrote this explainer in collaboration with Woodwell Climate Research Center. Dr. Marcia N. Macedo has been researching the Amazon since 2005, exploring how climate change and human activities are transforming the tropical landscape. At Woodwell Climate Research Center, she works in the field and at home to co-produce and translate research into relevant information for indigenous people and land managers. Dr. Macedo spoke to Probable Futures about her experience working in the Amazon and what the future might look like for this exceptional ecosystem.

Wildfires can have a profound impact on our global climate. Forests sequester massive amounts of carbon that help to hold back global warming, and when trees and other biomass burn in a wildfire, the carbon locked away in that organic matter is released into the atmosphere as CO₂. That CO₂ acts as a greenhouse gas, raising global average temperature.

In the Amazon rainforest, an ecosystem that plays a key role in regulating global temperatures, wildfire doesn’t occur without human intervention. In its undisturbed state, the Amazon is too humid for fire to spread, and ignition sources were historically rare. Now, as our planet warms, a combination of drought, higher temperatures, and human behavior are making wildfire more likely in the Amazon. Examining our change in wildfire danger days map in this area shows how higher warming levels impact the number of days in a year in which wildfire could spread.

The Amazon rainforest and the global climate

Climate zone: tropical

Population: 30 million (2020)

Risk factors: drought, wildfire

The Amazon rainforest, located mostly within Brazil surrounding the Amazon River and delta, contains 2.1 million square miles of dense rainforest—about half of our planet’s remaining rainforest, and the most biodiverse tract of tropical rainforest in the world. Tropical rainforests like the Amazon are estimated to be responsible for cooling the atmosphere by more than 1°C, with the Amazon storing more than 150 billion metric tons of carbon in trees and soil. Trees alone in the Amazon contain around 20% of all the carbon stored in plants around the world.

The cooling power of the Amazon rainforest is due to the local climate. The Amazon is very humid, rainy, and warm, contributing to rapid, biodiverse plant growth. The constant heat and humidity allows vegetation to grow so quickly that any decaying organic matter is absorbed into new growth before it can start emitting carbon. Because of this effect, the Amazon helps lower temperatures across the entire planet. 

I’ve been working in the Amazon since about 2001. I had a chance to visit when I was about 12—my family is originally from Brazil—and I was taken with the forest, diversity, people, biodiversity, and how dynamic the ecosystem is.

The Amazon at 0.5°C of warming

Because of the high rainfall and high humidity, wildfire does not occur in the Amazon without human activity. For wildfire to ignite and burn in the Amazon, conditions must be exceptionally dry, and ignition has to come from a human source.

Historically, indigenous groups used fire as a management tool on a small scale, and humidity and moisture impeded the spread of fire. Life in the Amazon adapted to conditions without wildfire, from the 16,000 tree species and thousands of animal species to the 350 ethnic groups and more than 30 million people inhabiting the region. The lack of fire allowed vegetation to accumulate. When the rare fires did burn, plants showed remarkable resilience and were able to quickly rebound.

At 0.5°C of warming, a degree of warming our planet experienced between 1971 and 2000, human activity began significantly changing the risk of wildfire in the Amazon.

Between 1970 and today, almost 20% of the Amazon rainforest has been lost to deforestation activities like logging and agriculture. This deforestation has had a direct impact on wildfire risk in the Amazon.

Wildfire was not something people worried about in the Amazon rainforest when I started working on it in 2005. In the last 20 years, that has totally changed.

Deforestation thins out the rainforest, releasing the moisture held inside the dense bubble of vegetation and resulting in drier conditions that cannot stave off fire in the same way. Humans often use fire as a clearing technique for agricultural needs, and even when people aren’t intentionally starting fires, the increased presence of humans and human activity results in more accidental fires. Rising global temperatures have also contributed to longer dry, hot spells in the Amazon, leaving trees less healthy and more vulnerable to fire. The risk of wildfire starting and spreading is greater now than ever before in the Amazon because of humans.

The future of the Amazon will be determined in large part by two factors: Local human activity and global climate change. Projecting to further degrees of warming, the map of change in wildfire danger days can tell us how global climate change may create conditions that increase or decrease the annual risk of wildfires spreading, given human ignition.

Wildfire danger days is a metric from the Fire Weather Index that determines how likely wildfire spread is, given the presence of burnable fuel and ignition, based on conditions of temperature and dryness. The factor of human behavior—how much of the Amazon we deforest, how frequently we start fires, and how rapidly or slowly our use of fossil fuels warms the planet—depends entirely on us.

The Amazon at 1°C and beyond

Our planet was 0.5°C above its pre-industrial average temperature between 1971 and 2000. More recently, we’ve moved past 1°C, so we use 1°C of warming as a proxy for the weather that we’re used to—the recent past.

At 1°C, the Amazon experienced up to 29 additional wildfire danger days in some places, as compared to 0.5°C. During any one of these days, conditions could allow a wildfire to burn and spread throughout the forest. The greatest increase in wildfire danger days is clustered around the Amazon river, from inland central Brazil to the Atlantic. Grid cells in this region are orange, meaning those areas experienced 14-29 additional wildfire danger days a year. 

Further into the rainforest and away from the edges of the Amazon river, the number of additional danger days is fewer, with most cells in the yellow 7-13 additional day range. Deep into the rainforest, most grid cells are gray, meaning the areas would not experience a statistical change in wildfire danger days.  

Dr. Macedo has seen recent changes to wildfire danger in the Amazon first hand:

“Wildfire was not something people worried about in the Amazon rainforest when I started working on it in 2005 because the climate was too damp to support it. There are no natural ignition sources for it in the Amazon. In other parts of the world, you have lightning that can light a fire spontaneously. That is not the case in the Amazon. You’d have a fire that, if it got out of control, would go out at night when the forest hit its dew point. In the last 20 years, that has totally changed. Now every time we have a major drought, you get these big upticks in wildfires.”

The next warming threshold, 1.5°C,  is impending (and the closest to the climate in 2024.) 2°C of warming is a potential future scenario. 

The transition of the Amazon from 1°C to 1.5°C is striking. Almost all gray cells have vanished, meaning the region generally is at risk for at least 7 additional wildfire danger days, compared to 0.5°C. While previously the orange cells indicating 14-29 additional wildfire danger days were clustered around the Amazon river, at 1.5°C most of Brazil is orange. The yellow 1-13 additional wildfire danger days cells are clustered mostly along the western edge of the rainforest. 

Focusing in on the region along the Amazon river between Manaus (the most populous city in the Amazon) and Santarem, some grid cells are now red, with 30-59 additional wildfire danger days in a year. Clicking on one of these cells to open the inspector box shows an average year with 30 additional wildfire danger days, and a drier year with 34. As the number of wildfire danger days increase, there is a higher risk overall that in a given year wildfire would ignite and burn.

At 2°C, the most striking change in the Amazon is the expansion of red cells. The spread of these cells show regions deeper into the forest bordering the Amazon river exposed to 30-59 additional wildfire danger days per year at this degree of warming. The rest of the Amazon at 2°C is in the orange 14-29 additional day range. Gray cells have nearly entirely vanished, and the yellow cells are pushing west towards the Pacific coast of South America. All of this increased danger—weeks of heightened wildfire risk, every year, in a region that historically did not burn—is only a half a degree of warming away from our level of warming in 2024.

2.5°C and 3°C of warming are potential but avoidable, depending on the pace and scale of human greenhouse gas emissions. 

At 2.5°C of warming, much of the Amazon is red, with 30-59 additional wildfire danger days a year. The red grid cells have spread deeper into the rainforest on either side of the Amazon river and towards the Atlantic coastline. The small cluster of gray cells along the Western edge of the Amazon rainforest has shrunk further, and there is now only a small portion of yellow grid cells in the 7-13 additional wildfire danger day range remaining.

At 3°C of warming, maroon grid cells appear around Manaus, indicating 60-155 additional wildfire danger days a year in that area. The inspector box for one of these grid cells reveals a projected 65 additional wildfire danger days in the average year and 72 in a drier year. The rest of the Amazon is mostly red and orange now, with 14-59 additional wildfire danger days a year. 

In a 3°C world, much of the year would be conducive to wildfire in the Amazon. Any human ignition could create an out of control fire, destroying dried-out trees. Depending on what deforestation and agriculture might have done to the rainforest, the remaining tree cover could be sparse and vulnerable. The ability of this once-dense forest to cool the global climate, rather than warm it, would be in question. The loss of a crucial amount of the Amazon rainforest represents a “tipping point” in the global climate: A point that, if crossed, might generate the hothouse earth trajectory.

As Dr. Macedo explains, the risk of losing the Amazon rainforest cannot be overstated: 

“If you removed all tropical forests on the planet, the global temperature would increase by one degree celsius. We can’t afford to lose these forests for that reason alone. It also is an important part of moving energy around the planet. It takes in solar energy through photosynthesis and accumulates carbon in its biomass. That process prevents that solar energy from sitting on the land surface and warming it. It acts like an air conditioner. It’s like a big swamp cooler, which is a huge service in a world where we’re trying to keep carbon from going up into the atmosphere and prevent further warming.” 

2.5°C and 3°C may be more distant thresholds of warming, but these projections give us an impression of what we need to avoid. Data like this can be as much a tool for anticipating risk as motivation to avoid harmful outcomes by limiting deforestation and slowing and stopping emissions. 

In the Amazon, wildfire is not a natural part of the system, but humans have created a situation where it’s more likely. Climate maps like change in wildfire danger days are really important because they can help us plan.

What could wildfire danger days mean for the Amazon? 

Climate maps are a useful tool for anticipating future outcomes. For wildfire danger days in the Amazon, the interactive map projects how many additional days in a year would be conducive to wildfire spread, but does not anticipate the human element to this climate risk. Human behavior is unpredictable and crucial to the future of this region and its impact on the global climate.

Here are a few guiding questions you can use to start considering wildfire risk in the Amazon:  

• Humans play a crucial role in starting wildfire in the Amazon. To prevent ignition on wildfire danger days, people need an understanding of what activities might start a fire and how to avoid them. This requires preparation and prevention, in the form of public outreach, education campaigns, and firefighter mobilization. When the number of wildfire danger days in a year is increasing by weeks and months, how can local regions stay prepared?  
• Deforestation is contributing to wildfire risk by thinning out the rainforest and increasing ignition likelihood. What could local governments do to provide incentives to prevent deforestation activities?
• Dr. Macedo explains, “The Amazon rainforest does have the capacity to heal itself if we get out of the way, and if we don’t keep up our pattern of repeated disturbances. It bounces back if we let it—not with the same level of biodiversity, but much of its crucial properties return.” Researchers have found some areas of the Amazon to be more resilient after wildfire than others, and have identified that animal activity like tapir grazing can accelerate reforestation by spreading seeds and organic matter. What targeted conservation or ecological efforts could support forest resilience and create a stronger rainforest?

Examining the range of possible outcomes for a climate impact in a place, putting that data in context, and looking for vulnerabilities is a framework you can apply to any place with any Probable Futures map. We offer maps of 30+ climate variables at warming scenarios ranging from 0.5 to 3°C degrees of warming. We invite you to explore and think about what climate impacts could mean in the places you care about.