Radios crackle with chatter from a wildfire incident command post. Up the fireline, firefighters in yellow jerseys are swinging Pulaskis, axlike hand tools, to carve a fuel break into the land.

By 10 a.m., these firefighters have already hiked 3 miles up steep, uneven terrain and built nearly 1,200 feet of fireline.

It’s physically exhausting work and essential for protecting communities as wildfire risks rise in a warming world. Hotshot crews like this one, the U.S. Forest Service’s Lolo Hotshots, are the elite workforce of the forests. When they’re on the fireline, their bodies’ total daily energy demands can rival that of the cyclists in the Tour de France, as my team’s research with wildland fire crews shows.

These firefighters are also caught in Congress’ latest budget battle, where demands by far-right House members to slash federal spending could lead to a governmentwide shutdown after the fiscal year ends on Sept. 30, 2023.

After extreme fire seasons in 2020 and 2021, Congress funded a temporary bonus that boosted average U.S. Forest Service wildland firefighter pay by either 50% or US$20,000, whichever was lower. But that increase expires after Sept. 30, knocking many federal firefighters back to earning the minimum $15 per hour.

Legislation to make the raise permanent is pending before Congress, which is now preoccupied. A short-term pay boost may be possible, but that doesn’t solve the long-term pay problem. And if the government shuts down, federal firefighters will be working without immediate pay. The National Federation of Federal Employees warns that a large number of firefighters could quit if their pay also drops.

Firefighters push their bodies to extremes

Life on the fireline is demanding. Pack straps dig into the neck and shoulders with each swing of the Pulaski. It’s a constant reminder that everything wildland firefighters need, they carry – all day.

The critical water and food items, supplies, extra gear and fireline tools – Pulaskis, chain saws and fuel – add up to an average gear weight often exceeding 50 pounds.

Hiking with a load and digging firelines with hand tools burns about 6 to 14 calories per minute. Heart rates rise in response to an increased pace of digging.

Measured with the same techniques used to quantify the energy demands of Tour de France riders, wildland firefighters demonstrate an average total energy expenditure approaching 4,000 to 5,000 calories per day. Some days can exceed the Tour’s average of about 6,000 calories, equivalent to around 12 McDonald’s Happy Meals. Add to that a daily water need of 1.5 to over 2 gallons.

This isn’t just for a few days. Fire season in the western United States can last five months or more, with most Hotshot crews accumulating four to five times the number of operational days of the 22-day Tour de France and over 1,000 hours of overtime.

The physical demand of a day on the fireline

My team has been measuring the physical strain and total energy demands of work on an active wildfire, with the goal of finding ways to improve firefighter fueling strategies and health and safety on the line.

The crew members we work with are outfitted with a series of lightweight monitors that measure heart rate, as well as movement patterns and speed, using GPS. Each participant swallows a temperature-tracking sensor before breakfast that will record core body temperature each minute throughout the work shift.

As the work shift progresses, the Hotshots constantly monitor their surroundings and self-regulate their nutrient and fluid intake, knowing their shift could last 12 to 16 hours.

During intense activity in high heat, their fluid intake can increase to 32 ounces per hour or more.

The highest-intensity activity is generally during the early morning hike to the fireline. However, the metabolic demands can sharply increase if crews are forced into a rapid emergency evacuation from the fire.

My team’s research has found that the most effective way for wildland firefighters to stay fueled is to eat small meals frequently throughout the work shift, similar to the patterns perfected by riders in the Tour. This preserves cognitive health, helping firefighters stay focused and sharp for making potentially lifesaving decisions and keenly aware of their ever-dynamic surroundings, and boosts their work performance. It also helps slow the depletion of important muscle fuel.

Although crews gradually acclimatize to the heat over the season, the risk for heat exhaustion is ever present if the work rate is not kept in check. This cannot be prevented by simply drinking more water during long work shifts. However, regular breaks and having a strong aerobic capacity provides some protection by reducing heat stress and overall risk.

The season takes a toll

Hotshots are physically fit, and they train for the fire season just as many athletes train for their competition season. Most crew members are hired temporarily during the fire season – typically from May to October, but that’s expanding as the planet warms. And there are distinct fitness requirements for the job. The physical preparations are demanding, take months and are expected, even when temporary crew members are not officially employed by the agencies.

Still, with the immense physical demands of the job, crew members often experience a decay in metabolic and cardiovascular health and an increase in cholesterol, blood lipids and body fat. It is unclear why such a hardworking job often makes firefighters less healthy, requiring an off-season reset to recover, retrain and rebuild.

The season causes damage. This unfolds counter to the commonly accepted benefits of regular exercise. Pollutant and smoke exposure, lapses in nutrition, sleep disorders and chronic stress during the season seem to gradually poke holes in the Hotshot armor.

Progressive intervention strategies can help, such as educational programs on specific physical training and nutritional needs, mindfulness training to reduce the risk of job-oriented anxiety and depression, and emotional support for crew members and families. However, these require agency and congressional investment, a commitment beyond ensuring pay raises remain intact. Removing either is synonymous with taking away critical tools for the job on the firelines.

Developing offseason practices that pay close attention to both physical and mental health recovery can help limit harm to firefighters’ health. Many Hotshots have bounced back and returned season after season. However, a government shutdown and failure to act on pay for front-line fire crews could worsen crew retention in an already dwindling workforce.

This is an update to an article originally published Aug. 8, 2023.

Brent C. Ruby receives funding from a wide range of DOD agencies to study human performance during environmental stress.

Life exists in every conceivable environment on Earth, from the peaks of towering mountains to the remote stretches of isolated islands, from sunlit surfaces to the darkest depths of the oceans. Yet, this intricate tapestry of existence isn’t spread uniformly.

For centuries, scientists have marveled at the extraordinary variety of species exhibited in tropical regions. The breathtaking biodiversity of the Amazon rainforest, the teeming life in Madagascar’s unique ecosystems, the species-rich cloud forests of Costa Rica – the tropics showcase nature’s opulence.

What makes the tropics so incredibly diverse?

Since the dawn of biodiversity studies, scientists have believed the predominant factor is climate – the long-term patterns of temperature, precipitation and other atmospheric conditions. Thinkers like Alexander von Humboldt set the stage in the early 19th century with their keen observations, highlighting how life-rich regions often shared certain climatic features. Fast-forward to the present, and scientists confidently correlate climate with biodiversity. Simply put, hotter, wetter, resource-rich regions are veritable cradles of life.

Some climatic conditions spread across vast landscapes, while others appear fragmented, resembling isolated islands amid varying climates. This difference raises an intriguing question: Is an area’s biodiversity solely due to its climate? Or do the size and relative isolation of these climatic pockets influence the richness and abundance of species that thrive within them?

We are part of an international, interdisciplinary team interested in the puzzle of how the geography of climate and the global patterns of species diversity fit together. Geography of climate is a bigger part of the biodiversity picture than previously assumed, according to our study findings recently published in the journal Nature.

Unraveling the geography of climate

Historically, to study global biodiversity patterns, researchers divided the world into equal area grids and counted the species in each square.

Our study diverged from conventional methods. Instead of focusing solely on specific geographical locations, we centered our attention on the unique climate profiles of regions. Essentially, we weren’t just looking at plots on Earth but every place that shared a particular set of climatic conditions. We then classified these conditions globally and meticulously counted the species – birds, mammals, amphibians and reptiles – that live within the boundaries of each climate.

Central to our investigation was an exploration of the geography of these climates, examining both their size and isolation. Some climates are widespread and common, sprawling over vast areas. Others are more fragmented, emerging as isolated pockets amid different climatic zones, reminiscent of islands in a vast ocean of other diverse climates. Consider tropical climates: They cover vast expanses cumulatively, despite being broken up into smaller, unconnected bits, even on different continents.

Our findings were illuminating. Climate, of course, was an important factor in how many species flourished in a location. But we were intrigued to find that about a third of the variation we found in species diversity across the globe can be attributed solely to the size and degree of isolation of all the instances of a particular climate.

Biodiversity responds not just to the type of climate but its spatial distribution. Beyond the known effects of warmth and moisture, we found that larger and more isolated climates foster greater species diversity. Moreover, these expansive, broken-up climates not only housed a greater number of species but also nurtured a more unique combination of species.

By leveraging but transcending traditional methodologies, our approach unearthed novel insights about the geographical characteristics of climates. We discovered that the larger a climatic zone is, the more fragmented and scattered it tends to be across the landscape.

Isolation spurs diversity

Traditionally, scientists have thought of tropical climates as cohesive expanses, standing as barriers between the distinct extra-tropical climates of our planet’s poles. Our analysis confirmed that cooler extra-tropical climates are relatively well connected across much of the planet.

Yet, our findings reveal a different narrative for the tropics: Tropical climates appear more as fragmented islands amid a sea of diverse climates, rather than expansive, interconnected realms. Our revelation underscores that tropical climates, while abundant, are dispersed and disjointed across the Earth’s surface.

Drawing a parallel, consider how mountainous regions harbor isolated valleys where people speak distinct dialects shaped by their seclusion. Nature mirrors this: Species in isolated climatic niches evolve distinctly, creating a diverse and unique tableau of life.

The specter of climate change, however, casts a long shadow over these insights. A world undergoing rapid warming might witness once vast climates fragmenting further. Such shifts could challenge species, compelling them to traverse daunting landscapes to find suitable habitats. If these once expansive climates recede, it could disrupt the entire balance of species interactions.

Understanding the interplay between biodiversity and climate is not merely an intellectual pursuit. It provides direction in helping people protect and appreciate the diverse symphony of life in our evolving world.

Catherine Graham receives funding from Swiss National Fund, European Research Council.

Dave Roberts received a stipend from WSL when he was a Fellow there during his stay in Switzerland when this work was initiated.

Marco Túlio Pacheco Coelho does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

When President Joe Biden created the American Climate Corps by executive order on Sept. 20, 2023, it marked a step toward keeping a pledge he made nearly three years earlier: to create a new workforce training and service program to deal with global warming.

The White House promises that the corps “will ensure more young people have access to the skills-based training necessary for good-paying careers in the clean energy and climate resilience economy.” By helping Americans get entry-level green jobs, such as solar panel installation and home insulation, it will equip thousands more young Americans to tackle the complex challenges posed by climate change.

As a scholar who researches and teaches about the history of U.S. volunteer service programs, I believe that the American Climate Corps will not provide anything radically new. Rather, it will largely offer the same experiences and work opportunities as an array of programs that already exist. But the Biden administration’s promise of connecting national service experience to long-term careers offers one important change to this model that I believe will make a difference to those who participate.

New Deal echoes

The inspiration for the American Climate Corps comes from President Franklin D. Roosevelt’s Civilian Conservation Corps. That New Deal program put unemployed – and mainly white – young men to work on public lands across the country to counter the devastating unemployment of the Great Depression.

Known as the CCC, it was a massive undertaking. Approximately 3 million men passed through its ranks over nine years. Those who served built much of the infrastructure of the country’s state and national parks, planted over 2 billion trees, fought forest fires and responded to natural disasters like floods.

The Biden administration aims to make its new corps far more inclusive in terms of gender, race and ethnic diversity. Rather than alleviating a short-term employment crisis, like its Depression-era predecessor, the American Climate Corps will emphasize launching careers.

So far it’s unclear how big this program will be. The White House has declined to specify a budget after repeatedly failing to persuade Congress to designate any funding for similar multibillion-dollar green jobs efforts because of Republican opposition.

Reportedly, the scaled-down American Climate Corps that Biden has bypassed Congress to establish could be funded through money appropriated to other parts of the government, such as the U.S. Agriculture Department, AmeriCorps and the National Oceanic and Atmospheric Administration.

The American Climate Corps, according to the details available, will mobilize far fewer participants than the CCC. The White House plans call for 20,000 people once it’s up and running, only 4% of the Civilian Conservation Corps’ peak enrollment of 500,000 men in 1935.

Network of similar programs already in place

This new service program is hardly the first to draw on the CCC’s example.

There are about 150 similar conservation service programs in the U.S., all connected through the National Association of Service and Conservation Corps. Known as the Corps Network, this patchwork includes 150 programs that give young adults and veterans opportunities to engage in service work on public lands and in rural and urban communities.

One of the oldest programs in what’s known as the Corps Network is the Student Conservation Association, founded in 1957. It puts thousands of high school and college-aged students to work on hiking trail improvement, tree planting and the restoration of natural acreage and waterways. Smaller programs like MobilizeGreen and New York City’s Green City Force focus on building a more inclusive green economy and training people for leadership skills or in tasks like building resilient urban food systems.

Many of these programs already get government funding through AmeriCorps, the federal agency for national service and volunteerism.

AmeriCorps also runs its own similar programs. The National Civilian Community Corps, established in 1993, deploys teams of young adults to projects that encompass energy conservation, infrastructure improvement, disaster recovery and response, and urban and rural development. Its website promises that “if you are 18-26, you can gain experience while supporting climate change mitigation.”

Operating since 1985, this amalgam of service programs already engages 20,000 young adults and veterans every year – the same number the Biden administration aims to mobilize. It’s unclear how the American Climate Corps might augment, replace or complement these programs. For instance, the corps’ focus on job training tied to solar, wind and other forms of renewable energy is relatively new – although some states have their own climate corps. Its emphasis on conserving land and water overlaps with the work existing state programs already do.

Scant objective evidence

There are different ways to assess whether service programs make a difference.

Many of them survey their participants, who regularly say they enjoyed the experience. Participants also cite a sense of personal growth, greater familiarity with environmental concerns and stronger leadership skills. One of the few studies conducted also found that people who took part in the conservation corps were more likely to pursue related careers.

These programs try to measure the impact of their work every year using metrics like hours served, miles of trails restored and acres of wetlands or forestry rehabilitated. But the data is largely self-reported and has never been rigorously or objectively collected and explored.

That means it’s hard to say whether funding these programs amount to an effective policy.

Better pay? Great opportunities?

Participants in the conservation corps programs that preceded Biden’s executive order get what amounts to small stipends and perhaps room and board. The low pay, which ranges from about US$16,000-$30,000 a year, can mean that they’re not an option for many recent college grads who might otherwise be interested.

Full-time AmeriCorps volunteers are also eligible to apply for grants to pay for their education or to make student loan payments on top of their earnings. These awards provide $6,895 in the 2023 fiscal year.

American Climate Corps backers argue it should pay a living wage as a form of “climate justice.”

It’s unclear whether the American Climate Corps will do that.

That’s why it’s important that the Biden administration is promising pathways to a high-paid career. It has outlined future cooperation between Americorps, the National Oceanic and Atmosphere Administration and the departments of Labor, Interior, Agriculture and Energy to help build links between American Climate Corps service and federal employment.

Answers to operational questions TBD

On top of the lack of clarity about its cost and funding and what participants will earn, it’s not clear to what extent the American Climate Corps will operate independently, or if it will support similar programs in the Corps Network.

For example, California, Michigan, Maine, Washington and Colorado already have their own climate corps. Five more states – Arizona, Utah, Minnesota, North Carolina and Maryland – unveiled their own when Biden signed the executive order for a national one.

Perhaps most importantly, it’s yet to be determined whether the American Climate Corps’ service work will differ from those state initiatives and similar programs. If not, this could simply be the rebranding of conservation programs as climate action.

Christopher Staysniak does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.