On April 20, 2023, the U.S. Department of the Interior (DOI) and Department of Agriculture (USDA) released a first-of-its-kind inventory of the country’s mature and old-growth forests. The assessment responded directly to a 2022 executive order aimed at fostering healthy forests.
The inventory highlights the importance of forest health in building resilience to future climate-related disturbances like drought or fire, but it omits mention of the service that all forests, but particularly mature and old growth forests, provide in directly mitigating the country’s carbon emissions—a service that Woodwell Climate’s scientists have worked to measure and monitor for over three decades.
The inventory is a critical starting point, from which agencies like the U.S. Forest Service and the Bureau of Land Management will begin to make decisions about how public forests are managed going forward. Not acknowledging the critical carbon storage contribution of mature and old-growth forests runs the risk of de-prioritizing protection for the country’s oldest, most carbon-rich, and hardest to replace ecosystems.
In short: carbon. While all forests sequester carbon as they grow, older and larger trees represent an existing store of carbon in their biomass and soil. Research by Woodwell Climate scientists on carbon stocks in a sample of federally managed U.S. forests found that while larger trees in mature stands constitute a small fraction of all trees, they store between 41 and 84 percent of the total carbon stock of all trees.
An analysis of mature and old growth forests across the country found that approximately 76 percent (20.8 million hectares) of these forests are unprotected from logging. This represents an amount of carbon roughly equivalent to 1 quarter of the US’s annual fossil fuel emissions.
Although younger forests grow faster proportionally, they are not adding as much carbon in a single year as older forests with large trees. Additionally, mature forests continue to pack away carbon year over year in their soils, which is largely protected from effects of disturbance. Cutting down a mature forest creates a “carbon debt” that can take decades—centuries in some cases—to recoup, and in the meantime those mature trees are no longer sequestering carbon each year.
“Forests are like naturally occurring factories, delivering to the planet the unique service of carbon sequestration. Trees of all sizes, but particularly large old trees, are the equivalent of warehouses where the goods produced—tons of carbon—are stored over time,” says Woodwell Climate Carbon Program Director, Dr. Wayne Walker. “Like any warehouse where valuable goods are stored, these natural carbon reserves deserve all the protection we can provide. Their loss could effectively bankrupt our efforts to avoid the worst impacts of climate change.”
Protecting mature forests requires them to be identified and mapped, which was part of the impetus behind the government’s forest inventory. But what actually is a mature forest?
Definitions of “mature” and “old-growth” differ, with no one universally accepted definition. Refining scientific understanding of what constitutes a mature forest has implications for either expanding or reducing the area of forest considered for protection.
In one study of U.S. forest carbon stocks, Woodwell Climate researchers and collaborators outlined a measure of forest maturity based on both the age that the tree canopy in a forest becomes 100 percent closed, called “Culmination of Net Primary Productivity,” and tree diameter size. Across 11 U.S. forests analyzed, the age at which a forest is considered mature ranged from 35 years in Appalachian forests to 75 in Arizona. “Old-growth” represents a smaller subset of mature forests having older and larger trees.
The new inventory from the DOI and USDA uses a slightly narrower definition of maturity, wherein the lower bound occurs when regeneration has begun underneath the canopy. This results in a slightly smaller estimation of the amount of mature and old-growth forests in the US—yet still approximately 63 percent of the total area of federally managed forests.
Other definitions can be based on models that take into account measurements of forest structure like canopy height, canopy cover, and biomass. Another study, co-authored by Woodwell Climate Assistant Scientist, Dr. Brendan Rogers, used these features to determine that federal lands contain the largest concentration of the country’s mature and old growth forests.
Differences in those definitions are important, because forest policy debates surrounding the responsible management of these forests depend on adequately identifying them, particularly mature forests, which are much more loosely defined than old-growth.
“I think the discussion is almost more about what to do with mature forests, as opposed to old-growth,” says Woodwell Climate senior scientist, Dr. Richard Birdsey, who worked in the U.S. Forest Service for four decades. “Mature forests are at a younger stage of growth—trees would be smaller, although they could still be substantial in size and very profitable to harvest. So the question here is whether to let those forests grow into old-growth characteristics, or to start harvesting them for wood products.”
When climate benefits are explicitly considered, the research points strongly to letting these forests grow—protecting and expanding the massive portion of sequestered carbon they represent.
According to Dr. Birdsey, the largest threat facing mature and old-growth forests in the U.S. is logging, which is a threat that humans can reduce instantly, simply by changing policy. A change that would make those forests more resilient to other threats in the long run.
“Others might argue that climate change or wildfire are more significant threats,” says Dr. Birdsey. “Older forests with larger trees are more resistant to those threats—but not more resistant to chainsaws. That’s a human decision.”
A recent paper in Nature Climate Change has laid out a “protect, manage, restore” framework for making decisions about what natural climate solutions to pursue, and the highest priority is always to protect carbon where it is already stored. U.S. policies have made some recent progress in this direction through the enforcement of the roadless rule on Alaska’s Tongass National Forest, prohibiting road-building and industrial logging on the 9 million acre temperate rainforest. But there is still further to go to capitalize on the carbon storage potential of the U.S.’s mature forests.
Federally managed forests contain more high-carbon trees than other lands, so the opportunity for increased carbon storage within them is greatest. Woodwell Climate Distinguished Visiting Scientist, Dr. William Moomaw, helped coin the term “proforestation” to refer to the strategy of letting forests continue to grow as a carbon solution. In order to achieve that, he says, mature forests have to be protected.
“The next steps should be to provide legal protection of as much of these high-carbon forests as possible,” says Dr. Moomaw. “These are public lands that should serve the public good, and reducing climate change is a public good that we should pursue as the highest priority.”
Transcript edited for grammar and clarity.
Sarah Ruiz: Fire. It’s a transformative force on any landscape, scorching and destroying, but often making space for new life. It also plays a part in transforming our global climate, releasing stored carbon from forests and other ecosystems that we simply cannot afford to add to our atmosphere. I’m here today with three of Woodwell Climate Research Center’s experts on fire and climate change: Dr. Manoela Machado, Dr. Brendan Rogers, and Dr. Zach Zobel. We’re here to discuss how fire fits into the climate change puzzle, as both a symptom and the cause of the warming climate. Consider this a “fireside chat” of sorts. Let’s begin.
Brendan, you work primarily in boreal forests, where fires are a natural part of the landscape, correct?
Dr. Brendan Rogers: Yes, that’s right. So even though boreal forests are in the north and they’re cold and damp for a lot of the year, the surface vegetation in the soil, the soil organic matter can dry out pretty dramatically in the summer. This fuel, as we call it in fire science, often all it takes is just one single ignition source to generate a pretty large wildfire. Humans certainly ignite fires, but still most of the burned area in boreal forests is coming from lightning ignitions.
Fire is also an important natural process in boreal forests. Many of the fires are what we call stand replacing—meaning they’re high intensity, they kill most of the trees, at least in Alaska and Canada. This initiates the process of forest succession, with often different types of vegetation, and tree species playing pretty key ecological roles. But fire regimes are changing and intensifying with climate change, taking us outside the range of what we would consider our natural variability that we’ve seen in these systems for millennia.
SR: Now, Manu, you work in the Amazon rainforest, where fire is never a natural part of the landscape. Can you explain what Kind of role fire plays in a tropical rainforest?
Dr. Manoela Machado: The Amazon biome did not evolve with fire pressure selecting for strategies of survival, which means that the plants are not adapted to this disturbance. Fire is a very powerful tool used to transform the landscape and has been used for millennia. Traditional and Indigenous communities still use it for agricultural purposes, but that’s not the fire that we see on the news, making headlines of “fire crisis in the Amazon.”
Those catastrophic events with lots of smoke in the atmosphere, they’re normally related to deforestation fires, which are fires used after clear cutting to clear out biomass and use the land for cattle ranching and other agricultural purposes. Those fires can escape into forest areas. So the ignition sources are always human—there are no natural ignition sources in the Amazon forest.
SR: With climate change, these dynamics are shifting in many places, as drier and hotter conditions make it easier for fires to spark. Zach, could you talk to us a little bit about what makes a forest susceptible to fire, and how climate change might be affecting that?
Dr. Zach Zobel: Fire weather is a given set of atmospheric parameters that indicate—if there was an ignition source—fire would be able to grow and spread rapidly. What we do is we model what is known as the fire weather index. This index consists of four different atmospheric variables, and those are: temperature (the hotter it is, the more likely vegetation is going to dry out quicker); relative humidity (the lower the humidity, the more rapidly vegetation can dry out); precipitation, both backward looking (“has it rained a lot recently”) and today; and wind speed, because once a fire starts, if the wind is adequately high, that’s when it’s going to spread.
We take those variables out of the climate models, and we model it—what it looks like historically, versus what it’s going to look like in the future. And what we find is that in several fire regimes, most of them actually, these “high fire risk days” are starting to rapidly increase.
We see it especially in the Mediterranean, Brazil, eastern Australia, the Western United States, in several parts of Africa. Over the next 30 years, we think these high fire risk days are going to increase on the order of a couple of weeks in some locations like the Western US, to upwards of one to two months in the Mediterranean and Brazil. And that’s pretty significant, when you think about how historically these days only occurred maybe one week a year.
SR: So what are some of the risk outcomes posed by those more frequent, intense fires, globally?
BR: More frequent intense fires are changing the ecology of many boreal forests in some cases, leading to transition from forest to grassland or shrubland, which of course impacts the resident animals. But there are also large impacts on humans. The smoke from large wildfire seasons is a direct threat to human health, and rural and especially Indigenous communities often feel the largest impacts. Additionally, in areas of permafrost, which is ground that is frozen year after year, fires can lead to permafrost thaw for many years. That can often destabilize the ground leading to ground collapse, presenting a hazard to people that are living in these areas.
MM: I think the Amazon has many similarities with the Arctic, despite being very different environments. Despite not being natural, fires have become a recurrent issue that coincides with the dry season, which then creates what we call the burning season. Any fire is damaging to an environment that is not adapted to it. So there’s the immediate release of huge amounts of carbon when that biomass is burning, and there’s the delayed mortality that understory fires cause, so there’s continued emissions of carbon as well. That can cause a shift in species composition.
And fire also begets fire, which means that forest canopy that is disrupted allows more wind and sun to penetrate the forest, which creates drier microclimates. And tree mortality increases the fuels on the forest floor as well. So a degraded forest becomes even more vulnerable to future burning. As Brendon mentioned as well, there are several studies linking the burning season with higher hospitalization rates of people with respiratory illnesses as well.
SR: So, then what do these changes mean in terms of fire risk? How much of what we’re seeing now is on par with or accelerated compared to what climate models have been showing?
ZZ: Manu, and Brendan just hit it right on the head. What we’re seeing is the driver of these increasing high fire risk days, is largely because the length of the dry season is increasing in many of these fire regimes. Since they talked about the tropics and the Arctic, I’ll use California as an example. The dry season is typically from April to November or December. What makes California almost even more unique is that if this extends later and later into November and December, that’s when the Santa Ana winds start to pick up. So we found that that’s what’s happening in California, the wildfire season is expanding into later in the season. And that’s when their seasonal winds start, ahead of the rainy season.
In terms of risk to life and property, there’s also another factor that I think is a little underappreciated. (and this is happening in the Mediterranean and Australia and some of the major spots I talked about, maybe less so in Brazil, but Chile as well) is people are moving into areas that traditionally have had wildfires, even in the absence of climate change. And so, as we continue to build up property, let’s say in California, in the wildland urban interface as it’s known, that’s when you start to see things unfold, like we saw in 2019, in Australia and the Camp Fire as well in California.
When we talk with our partners, we always show them how rapidly the climate models are viewing this increase in fire weather days. We definitely caveat it by saying, Here’s what the observations are showing us. The climate models aren’t even keeping up with how quickly wildfire risk days are increasing. So we view it as is “this is the best-case scenario for the next 30 years.” And the best-case scenario is scary enough. And that’s kind of the message we send to the people that we work with when presenting this data.
SR: Not only do increased fires have immediate ecological and safety impacts. They also represent a significant risk to our ability to achieve climate goals. Forests are one of our most valuable carbon sinks, and keeping them healthy and standing is essential to curbing warming. Let’s talk a little bit about how fires pose a threat to that.
BR: So boreal forest fires release some of the largest amounts of carbon per unit area for any biome on Earth. And this is because most of the fuel is coming from the soil organic matter or Duff. And most of the climate impacts are from CO2 and methane. But actually, there’s a whole host of gases that are released into the atmosphere. And what’s worse, in areas of permafrost, those fires can induce permafrost thaw and degradation that can also release even more greenhouse gases over the ensuing years. This is what triggers the global feedback mechanisms from boreal fires—climate warming, leading to more fires, which leads to more net emissions of greenhouse gases that further fuels climate warming.
When we combine the carbon release estimates from intensifying fire regimes with the interactions between fire and permafrost thaw, the numbers are somewhat sobering. And they may impact our ability to meet the global temperature targets such as one and a half and two degrees above pre-industrial as set out in the Paris Climate Agreement. These impacts are largely not accounted for in climate models or remaining carbon budgets. So, one big question is what can we actually do about it?
I first want to stress that the fires themselves are not the cause of the problem. They’re a system response to warming. So ultimately, the solution is reducing and eliminating fossil fuel emissions that are warming our climate. That said, we do actually have some level of control over boreal fires through fire management control that we don’t have, for example, when it comes to other bigger system feedbacks. Our group has done some work to show that boreal fire management and specifically suppression of fires when they’re first ignited and relatively small, could be a cost effective way to keep carbon in the ground and protect against rapid permafrost thaw. Actually recently, for the first time, a land management agency in the US has adopted these ideas and designated land in Alaska to be protected from fire purely for the purpose of protecting permafrost and carbon. Of course, there are many, many considerations that come into play with changing land management, for example, the ecological impacts, and of course, the people that live on or near that land, including indigenous communities. So these are really complex decisions. But ultimately, as we’re hopefully headed down a path towards global net zero emissions, towards climate stabilization and eventual climate cooling. I think that limiting boreal fire emissions should be considered as a natural climate solution that also has many co-benefits for the habitat, for human health, and the economy.
SR: So Manu, is fire management also a potential solution for the Amazon?
MM: Um, I don’t think it’s a solution, I think is something that exists, but also kind of in tune with what Brendan was saying that fire is not the core of the issue. In the Amazon, deforestation is the major issue regarding climate change in general. So, this process of land grabbing and clearing for cattle ranching and cropland is the driver of deforestation and for as long as we have that, we will have these catastrophic fire events. These deforestation fires and the leakage that comes from that into forest areas, those are not things that firefighters can face with safety. These are intentional fires, and they’re part of the deforestation process. So, the path to ending these fires is through tackling deforestation. The other types of fires such as pasture fires, forest fires that are not in those areas of like frontier of deforestation, they can be dealt with through prevention and combat actions, such as preparing firebreaks ahead of the expected burning season, and having well trained, well equipped brigades ready for action. And that’s something that we’ve been trying to do as well. We’ve been providing GIS training to Indigenous fire brigades across the Amazon and developed some other partnerships as well with spatial analysis and trying to help out with science too, but the core issue is not fire it’s deforestation.
SR: So, combating fires and learning to manage them when they arise is important, as well as working with communities on the ground to do so. But the root cause of climate change lies in the vast amount of carbon emissions that are released by human activities. Ultimately, bringing fires under control will require mitigating emissions and curbing climate change, otherwise, forest fires might just become too hot to handle. Thank you, everyone, for sharing your perspectives on fire and climate change with us today.
In terms of climate mitigation, forests are like green gold—working overtime to cool the planet, while also supporting a wealth of biodiversity. But we have not been saving them as one would a precious asset. Despite pledges to end deforestation, old growth forests are being cut down at alarming rates. And planting new trees is widely prioritized and incentivized over protecting existing forests. Across the board, standing forests are vastly undervalued. This has to change if we are to stand a chance of limiting warming to internationally agreed targets.
According to a recent study from scientists at Woodwell and the University of Virginia, tropical forests alone are holding back approximately 1 degree Celsius of warming. About 75% of that cooling effect is due to carbon sequestration. Forests grow, trees lock away carbon in their trunks and roots and shunt it into the soil. The other 25% comes from the innate properties of forests that work to cool vast regions of the globe.
Through photosynthesis, plants release water vapor into the air in a process called evapotranspiration. The vapor contributes to cooling near the ground, as well as cloud formation higher in the atmosphere that reduces incoming solar radiation. The shape of the tree canopy also contributes. So-called canopy “roughness” disrupts air flow above the forest. The more uneven the canopy, the more turbulent the air, which disperses heat away from the surface. In the tropics, evapotranspiration and canopy roughness are high, which means that surface temperatures remain relatively low, with the heat dispersed throughout the deep atmosphere.
Forests also naturally produce molecules called biogenic volatile organic compounds (BVOC), which can either contribute to cooling by encouraging the formation of clouds, or to warming by creating ozone and methane. In the tropics, the net effect of these chemicals is cooling.
The cumulative result of these properties is that when forests are removed, the land around them begins to heat up even faster, which can increase the frequency of extreme heat and drought events. Without forests, some regions will become a lot less resilient to sudden shocks. And the release of carbon contributes to global warming which further exacerbates hot, dry conditions.
“Forests act like air conditioners,” says Woodwell Assistant Scientist, Dr. Ludmila Rattis, who studies the impacts of deforestation on agriculture in Brazil. “Deforesting in the face of climate change is like getting rid of your air conditioners before an upcoming heatwave.”
Protecting forests, and maintaining the cooling services they provide, is vital to limiting warming. But, with forests covering 30% of the Earth’s land, prioritizing protection is a massive task. And when it comes to carbon storage, not all forests are equally valuable. Older, healthier forests tend to have a more secure hold on their carbon.
“Mature forests have higher biodiversity and create their own microclimate,” says Woodwell Associate Scientist, Brendan Rogers. “They’re more resistant to drought and other types of disturbance. And because of that, they tend to be more stable in the face of environmental perturbations over time.”
New research from Woodwell and Griffith University has developed a method of identifying high-value forests using satellite imagery. Estimating the metric of “forest stability” through satellite data on the light reflected by vegetation and a water stress index of the tree canopy, researchers were able to determine gradients of stability within forest patches in the Amazon and boreal forests.
Using a gradient of forest stability allows for a better prioritization of forest protection strategies based on their carbon value.
“The first priority is to protect stable forests from further human disturbance,” says paper co-author Dr. Brendan Mackey. “The second priority is to identify forest areas where restoration efforts will be most cost effective.”
But if the state of existing forests is any indication, forest protection continues to be deprioritized. Many wildfires are left to burn unless they threaten human settlements. Governments continue to incentivize deforestation for development or agricultural expansion. Indigenous and local communities are not compensated for their work stewarding their territories and keeping forests safe. And the warmer the planet gets, the more susceptible even protected forests become to drought, fire, and disease.
Research has shown that stewarding standing primary forests, and reviving degraded ones, represents the greatest opportunity for near-term carbon storage and removal. A study of global land-based carbon storage potential found that improved management of existing forests alone could store approximately 215 billion metric tons more than they currently do.
Protecting forests is cost effective, too. For example, in the United States, investing in fire fighting in Alaska’s boreal forests would require just $13 per ton of CO2 emissions avoided. That’s easily on par with other mitigation strategies like onshore wind or solar energy generation.
Effective strategies for protecting forests already exist, they’ve just been suffering from a lack of force—and often funding—behind their implementation. For example, forest carbon markets—where landowners and forest stewards are paid to protect standing forests that are otherwise vulnerable to deforestation—have the potential to keep forests safe while offsetting emissions from other sectors. But nascent carbon markets are inefficient, with weak standards for verifying the quality of credits being sold, and lacking the transparency needed to ensure credits are actually reducing overall emissions, rather than greenwashing carbon-intensive business practices.
Credits are also priced incorrectly for their relative climate value—the market currently values reforestation credits more highly, reducing incentive for landowners to conserve standing, old-growth forests when there is a better livelihood to be made in legally deforesting land for other uses. A truly effective carbon markets system would require large investments in science that can verify credit standards.
Forests are like our global carbon savings accounts—when we cut them down, we’re drawing out money and limiting our ability to collect interest and keep growing our funds. Successful mitigation can’t be accomplished without taking the full value of forests into account and strengthening policies to reflect that. If they aren’t, the planet will pay a far greater price for it as temperatures rise.
“We can’t afford to keep cutting forests. We need to reduce emissions now, and protecting forests is one of our best available solutions. Despite the obstacles, it’s worth the investment,” says Dr. Rogers.
The first designated Indigenous land in Brazil, Território Indígena do Xingu (TIX), has been cited by studies for decades as a successful buffer against the deforestation, degradation, and fires that plague other parts of the Amazon. A recent study, co-authored by Dr. Divino Silvério, Professor at the Universidade Federal Rural da Amazônia, and Dr. Marcia Macedo, Woodwell Water Program Director, shows that fire regimes are changing in the Xingu region, leading to more forest loss and degradation.
The paper shows roughly 7 percent of the TIX has been degraded by drought and fire. Degradation is part of a feedback loop wherein damaged forests become drier and more susceptible to burning in future fires.
“I remember when I started my Ph.D., a 2006 paper showed that Indigenous lands were extremely effective fire breaks—the Xingu just never saw fire. Climate change has completely changed that story,” said Dr. Marcia Macedo.
Indigenous communities in the TIX have been managing the rainforest for centuries with finely adapted slash and burn cycles that create space for agriculture and promote the growth of natural species used in construction, medicine, and cooking. These cycles can last three to four decades before an area is burned again. Traditionally, burns were well controlled and the rainforests surrounding burned areas were healthy enough to prevent flames from escaping.
But over the past two decades, the paper observed, escaped fires have occurred more often within the reserve and the likelihood that forest is lost post-fire is rising, particularly in seasonally flooded forests. Indigenous management practices have not changed significantly, the paper explains, so why the increased prevalence of fire and degradation?
Climate change is drying out forests, making them more susceptible to escaped burning from management practices. The other factor driving degradation within the territory is growing population. Indigenous communities are becoming less nomadic, and village populations are rising, increasing the area of forest used for subsistence. Degradation was higher in areas surrounding villages.
“The way Indigenous people manage fire has stayed the same, but we now have a different climate,” said Dr. Divino Silvério. “Indigenous people have been in these regions for many decades or centuries. And all this time they have had their own fire management to produce food that usually doesn’t end in these huge forest fires.”
Climate change will force Indigenous communities within the reserve to adapt traditional practices to protect the forest against more frequent, intensifying fires—despite these communities not contributing to global emissions.
Previous attempts to manage increasing fires through prescribed burning have clashed with the needs of residents of the TIX. Burning at a different time of year does not cultivate the same species, and residents were concerned it was jeopardizing the growth of plants used for medicine.
Dr. Silvério is working with residents of the Xingu to understand how to integrate changes to fire management practices with traditional strategies in a way that supports community needs. One example, he said, could be shifting the primary construction material from grasses (that grow after fire) to palms.
“Indigenous people will probably need to learn how to live in this new reality, an environment with more drought and more fires. We are trying to work in a participative way to construct solutions with them.”
Though droughts and bad harvest years are occasional risks for farmers, modern agriculture is built on the assumption of a predictable and stable climate. Rising temperatures are breaking down that assumption, leaving the future of food uncertain. Two new studies put the increasing risks in sharp relief.
Seventy-two percent of today’s staple crops—maize, wheat, soybeans and rice—are grown in just 5 countries, in regions of the world known as breadbaskets. From the plains of North America to the river valleys of India and China, these regions earned their distinction for supporting hundreds of years of agricultural production with their climatic suitability.
“These regions have developed this way for centuries in the same way that human settlements have developed around water, because that’s where the resource was,” says Woodwell Research Assistant, Monica Caparas.
Caparas works on agricultural risk models. Last year, she led an analysis of crop failures in global breadbaskets, projecting the likelihood of declining yields in the upcoming decades. Her results conjured a world where these centuries-old food producing regions may no longer be so reliable. By 2030, crop yield failures will be 4.5 times higher. By 2050, the likelihood shoots up to 25 times current rates.
By mid-century, the world could be facing a rice or wheat failure every other year, with the probability of soybean and maize failures even higher. A synchronized failure across all four crops becomes a possibility every 11 years.
If that sounds like rapid, drastic change, that’s because it is. The immediacy of increasing failures surprised even Caparas.
“The fact that by 2050—which we are almost halfway to already— there could be a wheat failure every year. It’s startling.”
One major component of crop failure predictions is water scarcity. In a warmer world, water is a critical resource. Climate change will shift precipitation patterns, drying out some regions and inundating others. Most of the world’s breadbaskets are headed in the drier direction.
Caparas factored water availability into her analysis, finding the likelihood of crop failure much higher in water scarce sections of breadbaskets. Wheat is especially water dependent, particularly in India where 97% of wheat crops are growing in areas already experiencing water stress. Irrigation could make up for some lack of rain, but groundwater stores are already overdrawn in many places.
In Brazil, agriculture is already showing signs of declining productivity from changing precipitation. Woodwell Assistant Scientist Dr. Ludmila Rattis works in Mato Grosso, where she researches the impacts of agriculture and deforestation on the regional climate. Central Brazil is a major breadbasket for soybeans and maize—as well as cattle— and as crop demand increases, farms and ranches have advanced into the Amazon rainforest and the Cerrado, the Brazilian Savanna.
Clearing and burning forests not only releases carbon that contributes to rising global temperatures, it can also have drying effects on the local watershed. In recent years, farmers in Mato Grosso and the Cerrado have reported issues with dry spells, though they would not attribute it to climate change. Dr. Rattis wanted to quantify these anecdotes to show that they were connected.
“I was trying to see why they were denying the climate changing at the same time they were feeling the climate changing. Were they feeling that in their pockets? Was it affecting the finance of their business?”
Dr. Rattis modeled temperature and precipitation changes along Brazil’s Amazon-Cerrado frontier. Her results not only predicted that by 2060, 74% of the region’s agricultural land would fall outside of the ideal range of suitability for rainfed agriculture, they showed that nearly a third of farms already did.
The changes are affecting crop productivity. When the temperature gets warmer, plants grow faster, releasing more water vapor into the air from their leaves as a byproduct of photosynthesis. If there isn’t a steady supply of soil moisture available to replace the lost water, plant growth is stunted. Rainy seasons are also starting later, limiting the possibility for planting two rounds of crops in a single season, which cuts into farmer’s profits and encourages further expansion via land clearing.
Caparas notes that increasing crop failure doesn’t necessarily mean we are headed for a world without maize or soybean. But it does mean a drastically different agricultural system— one where hard decisions have to be made about land use.
“Increasing crop failures doesn’t mean that these crops won’t ever be able to grow in these areas again, or that they should be abandoned, just that it’s going to be much harder for them to be as productive,” Capraras says. “There might be a certain threshold of losses that would lead people to leave these croplands.”
There is some potential for migration of the most productive lands as northern latitudes begin to warm. Caparas’s projections showed the greatest likelihood of breadbasket migration from the United States into Canada.
However, just because the climate suitability is migrating, doesn’t mean agricultural production will shift along with it. Other factors including soil fertility or existing land uses could limit the practicality of moving to new regions, especially if it jeopardizes existing climate solutions as the case in Brazil has shown. Clearing forests is only accelerating warming, drought and declining productivity.
Shoring up food security in a changing climate will require system-wide changes to our current agricultural system. Part of that starts with adjusting farming strategies to mitigate the effects of the warming that’s already unavoidable. Dr. Rattis has begun outreach to the farmers whose land she collected data on, giving them a picture of what their farms will look like if nothing changes.
“We need to make them feel that they’re part of the research, because they are. If we do, once we get the results, the probability of them using those results to adapt the way that they produce food will increase,” Dr. Rattis says. “They can see themselves in the historic part of the graphic and then I show them where, climatically speaking, their farm is going,”
She’s hoping these conversations will open Brazil’s farmers up to practices that leave more native vegetation on the landscape, which would help stabilize the local climate and keep the natural watershed intact.
Caparas takes hope from the fact that the outcomes of her models are not set in stone. In the planet-wide experiment of climate change, we can affect the results.
“These projections are due to changes in climate. They don’t account for adaptation strategies. The agricultural technology industry is fast-growing and so I think that there is hope, as long as adaptation techniques are implemented equitably,” Caparas says.
Much of the innovation, Caparas says, will have to involve developing drought resistant crop varieties and less water intensive agricultural processes. In the long term however, securing a productive agricultural future for the Earth’s nearly 10 billion people by 2050 will depend on securing a stable climate.
“First and foremost it always has to be getting climate change in check,” says Caparas.