Wildfires Are Increasing CO2 Emissions, and Animals Are Adapting

Scenes of devastation from wildfires have almost become a staple of summer in the past decade. In addition to the physical destruction they cause, wildfires release carbon dioxide (CO2) and other greenhouse gases into the air that contribute to climate change. In 2021, CO2 emissions from wildfires reached a record high, equaling nearly twice as much as that from global aviation. If this scale of emissions from unmanaged lands becomes normal, say researchers, stabilizing Earth’s climate will be even more challenging than we thought.

To combat that trend, scientists have turned their gaze on our increasing number of wildfires. They’ve found that in America’s dry conifer forests, fires are burning hotter and killing more trees today than in previous centuries. The main culprit? Paradoxically, a lack of fires.

Interestingly, however, in response to this era of larger, more destructive and longer-lasting fires, animals and plants are quickly evolving to cope. By gathering and analyzing the wide body of research about rapid animal evolution in response to fire, ecology experts hope to leverage what we already know to develop better, evolution-informed conservation plans. Hopefully, then, we can try to harness the ways in which fire impacts animals to protect vulnerable species; in other words, work with evolution instead of against it.

Wildfires emit record-breaking CO2

For the first two decades of the 21st century, global wildfire carbon emissions were relatively stable at about 2 gigatons per year. But in 2021, emissions really took off. Nearly half a gigaton of carbon (or 1.76 billion tons of CO2) was released from burning boreal forests in Eurasia and North America. That’s 150% higher than annual mean CO2 emissions between 2000 and 2020, reports an international team of researchers led by Earth system scientists at the University of California, Irvine, in a paper in the journal Science in March 2023.

The fires, conclude the scientists, are two decades of rapid warming and extreme drought in Northern Canada and Siberia coming home to roost; and, unfortunately, they say, even this new record may not stand for long. The escalation of wildfires in the boreal region is anticipated to accelerate the release of the large amounts of carbon stored in the permafrost, as well as contribute to the northward expansion of shrubs. And those two factors could potentially lead to further warming and create a more favorable climate for the occurrence of wildfires.

Analyzing the amount of carbon dioxide released during wildfires is difficult for Earth system scientists for a variety of reasons. Rugged, smoke-enshrouded terrain hampers satellite observations during a combustion event, and space-based measurements are not at a sufficiently fine resolution to reveal details of CO2 emissions. Models used to simulate fire efficiency, fuel consumption and fuel load work well under ordinary circumstances, but they are not robust enough to represent extreme wildfires. And there is another roadblock of our own creation: Earth’s atmosphere already contains large amounts of carbon dioxide from our fossil-fuel burning, and the existing greenhouse gas is difficult to distinguish from that produced by forest fires.

The University of California, Irvine, team, however, found a way around these hurdles by studying carbon monoxide (CO) expelled into the atmosphere during blazes. Combining CO readings from MOPITT—the Measurements of Pollution in the Troposphere satellite instrument—with existing fire emissions and wind-speed datasets allowed the team to reconstruct changes in global fire CO2 emissions from 2000 to 2021. Carbon monoxide has a shorter lifespan in the atmosphere than CO2, so if scientists detect an anomalous abundance of CO, that provides evidence of fires. The researchers then independently confirmed the occurrence of extreme fires in 2021 with datasets provided by NASA’s Moderate Resolution Imaging Spectroradiometer aboard the Terra and Aqua satellites.

The researchers said their data analysis revealed links between extensive boreal fires and climate drivers, especially increased annual mean temperatures and short-lived heat waves. They found that higher northern latitudes and areas with more extensive tree cover were especially vulnerable.

Although about 80% of these CO2 emissions will be recovered through vegetation regrowth, 20% will be almost irreversibly lost to the atmosphere. That means we’re going to have to find a way to remove that carbon from the air or substantially cut our production of atmospheric carbon dioxide.

Prescribed fires reduce fire severity

America’s dry conifer forests are no strangers to fire; historically, these forests burned every five to 35 years. Historical fires were generally of low to moderate severity, which meant many trees survived. Starting in the late 1800s, however, fire was effectively excluded from dry conifer forests. This was primarily due to a trio of causes: direct fire suppression, intensive livestock grazing and the forced disruption of cultural burning, a well-documented practice for many Indigenous communities prior to colonization. In the absence of fire, these forests have grown denser as flammable materials, such as leaf litter and dead trees, have built up. This has triggered concern that today’s fires will be hotter and more severe compared to those that burned prior to 1875.

To address that worry, research ecologists with the U.S. Forest Service Rocky Mountain Research Station used satellite data to characterize fire severity in dry conifer forests during a contemporary time frame (1985–2020), then compared it to fire severity during a historical time frame (1600–1875). Their results show that without frequent, low-severity fires like those experienced in the past, today’s fires are more severe and more likely to kill trees. Such extensive burning over time threatens the long-term survival of dry conifer forests.

Scientists were also able to compare areas designated as federal wildernesses with those that are not. They found that non-wilderness areas experienced slightly more severe fires than wilderness areas. As commercial enterprises such as logging are restricted in most wilderness areas, this suggests that the absence of historical fires and the resulting buildup of flammable materials play a larger role in today’s increasingly severe fires than historical logging activities.

As a case study, scientists looked at the Gila Wilderness in New Mexico. In the Gila, they found that a decades-long policy of managing fire, including allowing it to burn in certain scenarios, lessened the severity of fires in dry conifer forests from 1985 to 2020 compared with other areas in the Southwest that were a focus of the study.

These results, published in the September 2023 issue of Forest Ecology and Management, reinforce the concept that low-severity fire begets low-severity fire, and they demonstrate that frequent low-severity fire is possible even as our climate has become drier and warmer. The scientists believe that the Gila Wilderness approach—in addition to prescribed burns and other management actions that reduce fuels—could serve as a road map for restoring resilience to dry conifer forests across the western U.S.

Fire regimes cause animals to evolve

In response to climate change and land-use changes, fire regimes—or the typical characteristics of fire in a particular place, including frequency, severity, shape and size—are quickly changing. Every inch of terrestrial Earth containing vegetation and an ignition source has an associated fire regime. In many ecosystems, fire is the major agent of landscape modification.

Fires today are remodeling vegetation patterns, morphing habitats and causing species to face large-scale mortality and dispersal events, which means that large numbers of individuals are being killed or driven into new regions, sometimes dividing populations into different groups. Animals are also evolving.

By synthesizing the wide body of research about rapid animal evolution in response to fire, a multidisciplinary team of ecology experts hopes to help conservationists.

Animal evolution in response to fire is generally less well understood than that undergone by plants. So, the ecologists wondered what there was to learn from compiling what we know about how fires impact animals. They reviewed nearly 100 papers to identify examples of animal evolution in response to fire—and to analyze and categorize the different ways in which this evolution can take place. Their results were published in the journal Trends in Ecology and Evolution in July 2023.

One example is Melanophila beetles, which have evolved infrared sensory pits that allow them to detect forest fires and safely engage in reproductive behaviors near them. Other species, such as a bird called the Temminck’s courser, which lays eggs the color of recently burnt ground, have evolved by changing their basic biological characteristics. A behavioral adaptation was discovered in Australian frilled lizards, who hide in trees to escape fires.

Understanding the variation in how animal species are evolving or changing their behaviors because of fires is important because it will enable more effective conservation efforts. In some cases, artificially introducing fire into an ecosystem may even help make species more resilient. The ecologists mention one plan being considered by conservationists in Yosemite National Park, where fire could be used to help separated populations of Boisduval’s blue butterflies become more connected, allowing them to better reproduce, improving their genetics and increasing their population numbers.

Worsening wildfires inspire action

As I write this, wildfires are tearing through the Hawaiian island of Maui. At least 96 people have died, making the wildfires the deadliest in the U.S. in more than 100 years.

Maui is just one example of our era’s worsening wildfires. But there are ways our leaders can act—such as making buildings fire-resistant, utilizing prescribed burns, tackling the climate crisis, equitably engaging local communities, ensuring sustainable land-use management, and building back greener and safer—and methods we can adopt to reduce our own fire risk, such as developing family safety plans.

Wildlife is already adapting, adjusting and evolving to deal with the new reality of our wildfires. We will need to do so, too.

Here’s to finding your true places and natural habitats,

Candy