Snowmobiles in Yellowstone National Park:
An American right, or wrong?

Created by Jen Millner, Geoscience Education Web Development Team, Montana State University

This module includes information and resources about:
Impacts on Air Quality :: Impacts on Snowpack Chemistry and Water Quality :: Impacts on Wildlife :: Noise Level Impacts :: Economic Impacts :: Public Opinion :: Proposed Solutions and Alternatives :: Particulate Emissions

You will also findTeaching Activities to help teachers and students utilize and integrate the information into the classroom.

Snowmobiles in Yellowstone National Park. Details
More than three million people travel from around the world to visit Yellowstone National Park each year. Most people vacation during the summer months, when the air is warm, the days are long, and the roads are clear. But nearly 125,000 visitors prefer to wait until the coldest, darkest, snowiest time of year precisely because the weather is inclement and the roads are impassable. They go to experience the wonders of Yellowstone on a snowmobile.

About 640,000 years ago, a cataclysmic volcanic event of a scale not known in human history disgorged a volume of ash so immense that it covered all of the western U.S., as well as parts of the Midwest, northern Mexico, and some areas of the eastern Pacific. The colossal eruption left a massive caldera 30 miles wide and 45 miles long, an area we know today as Yellowstone National Park.

Once called "the place where hell bubbles up," interest in the region's astounding geothermal features led to the creation of the world's first national park in 1872. It continues to be most famous for its multitude of geysers, mud pots and hot springs, the total amount of which out number the rest of the world combined. The park also contains the greatest concentration of wildlife in the lower 48 states - mighty moose, great herds of elk, elegant swans, fearsome grizzly bears, elusive gray wolf, and the majestic bison, the only wild bison herd that has survived continuously since prehistoric times and the last free-ranging herd on earth.

What is the controversy all about?

Snowmobiling in the park is controversial on several fronts. Conservationists are concerned about how snowmobiles, and snowmobile emissions in particular, may impact wildlife, air and water quality, noise levels, and the pristine aesthetic of the Yellowstone wilderness. Another concern is for the health effects upon both snowmobile riders and park rangers who are exposed to exhaust and high noise levels for significant amounts of time. Supporters of snowmobiling point to other considerations such as the economic benefits to local communities and the importance of preserving access to public lands. They also contend that newer technologies make cleaner, quieter snowmobiles that mitigate the effects of snowmobile use on air, water and noise pollution.
Ultimately, the fundamental question is this: Is the park a place which is meant to "conserve the scenery and the natural and historic objects and the wild life therein," as stated in the Organic Act of 1916, or is it "a public park or pleasuring ground for the benefit and enjoyment of the people," as stated in the 1872 dedication of Yellowstone as the world's first national park?

When it comes to conservation versus public access, where do you draw the line?


Winter visitors at Old Faithful, Yellowstone National Park. Details

Snowmobiles were first allowed into the Park in 1963. At the time, the National Park Service (NPS) encouraged sensible snowmobile use in the Park as a way to increase winter visitation. But as snowmobile visitor numbers have grown to more than 75,000 each winter - up to 720 per day - so has concern for the effects that snowmobile emissions, noise, and crowds have on the health of the Greater Yellowstone Ecosystem and those who enjoy it.

Winter use first became a legal issue in 1997 when the animal rights organization Fund For Animals filed a lawsuit to ban all snow grooming of paved roads in the Park, effectively banning snowmobiles because they are only allowed to travel on groomed roads. Upon settlement of that suit, the Park and the NPS began to develop a new usability plan and environment impact statement (EIS) which led to a Record of Decision in 2000 to ban all snowmobiles within the park. This ban became effective in April 2001. A subsequent lawsuit filed by snowmobile manufacturers and supporters prompted a second, supplemental EIS (SEIS) and ultimately overturned that ban in 2003. Legislation continues to be hotly debated while public opinion remains strongly polarized. With both sides still actively pursuing their interests the issue remains unresolved.

Learn more:

Final Rule (more info) - provides background information about the legal events leading up the 2004 decision, a summary of responses to public comments, and economic analyses of proposed alternative management plans.

Yellowstone's Temporary Winter Use Rules

Environmental Issues

Impacts on Air Quality

Snowmobiler with filter mask. Details

One of the biggest concerns about snowmobiling in Yellowstone is whether or not snowmobile emissions cause air pollution. Those opposed to snowmobiles attest that emissions can lead to health problems for park employees who are subjected to prolonged exposure, while snowmobile supporters contend that the toxicity levels of emissions and exposure rates are not significant enough to cause harm.

Most snowmobiles currently in use have two-stroke motors that pass 20-33% of the fuel straight through the engine and out the tailpipe unburned. Standard two-stroke engines also require that lubricating oil be mixed with fuel, so lubricating oil makes up part of the exhaust. This creates most of the visible haze that snowmobiles produce in the form of particulate matter, which itself is composed primarily of volatile organic compounds and hydrocarbons.

Under Yellowstone's Temporary Winter Use Rules, snowmobiles must meet the NPS's Best Available Technology (BAT) standards for noise and exhaust emissions, including carbon monoxide, unburned hydrocarbons and volatile organic compounds, oxides of nitrogen, and particulate matter. These compounds are common mobile source emissions.

Carbon monoxide (CO) is a colorless, odorless gas produced from the incomplete combustion of carbon-based fuels. When inhaled, it hinders the oxygen-carrying capacity of blood and reduces delivery of oxygen to the body's organs and tissues. Carbon monoxide toxicity may cause cardiovascular and neurological impairments.

See more about carbon monoxide:

Oxides of nitrogen (NOx) cause a wide variety of health and environmental impacts because of various compounds and derivatives in the family of nitrogen oxides. It can be an irritant to eyes, nose, throat and lungs. In the environment, it contributes to air pollution, acid rain, and even global warming.

See more about oxides of nitrogen:

The potential health impacts of particulate matter (PM) are two-fold. Most PM is in the "ultrafine" range (less than 100nm) which means that it is respirable and may be deposited in the lungs. Additionally, volatile organic compounds (VOCs) are well-established as possible carcinogens.

See more about particulate matter and volatile organic compounds:

Particulate Matter Volatile Organic Compounds
Air Pollution and Health (more info) offers a summary of the above compounds.

What do you think? Compare the information you've just read with the graphs below.

Click on the image to see a chart of comparative HC, CO, and NOx emissions for different types of engines and vehicles.
Click on the image to see charts of carbon monoxide and hydrocarbon emissions by vehicle type.
Click on the image to see a comparison of emission ratios of selected compounds from two-stroke and four-stroke snowmobile exhaust.

Which type of engine emits the most toxins?
Inversion over the Grand Canyon. Details

Newer four-stroke engine technology reduces levels of some of these emissions, as well as reducing noise output of the snowmobile. Unfortunately, reducing emission levels does not necessarily reduce the concentrations of those emissions in the air in Yellowstone. The reason is weather. Concentrations may vary depending on wind, temperature, sunlight and inversion.
A temperature inversion occurs when a layer of cool air is trapped at ground level by an overlying layer of warm air, which can also trap pollutants. Many factors can lead to an inversion layer, such as temperatures that remain below freezing during the day, nighttime temperatures in the low teens to single digits, clear skies at night, and low wind levels - all common conditions during a Yellowstone winter.

What do you think?
  • How would an inversion effect the dispersion of snowmobile emissions?
  • How would this distribution influence health?

Impacts on Snowpack Chemistry and Water Quality

Snowmobiles in Yellowstone National Park.
Snowmobiles in Yellowstone National Park. Details
One of the least-studied aspects of the environmental impact of snowmobile emissions is their potential effect on snowpack and localized water quality through snowmelt runoff. Quantitative research is sparse and many questions remain unanswered.

In one study, samples taken from the on-road snowpack near West Yellowstone, the most heavily traveled snowmobile route into the park, contained several varieties of PAHs and VOCs known to be major ingredients in two-stroke engine lubricants. Samples taken in Gallatin Canyon where there is car traffic but no snowmobiles did not contain these compounds.

Click on the table to see concentrations of n-alkanes and n-alkyl acids (hydrocarbons) on snowmobile routes.

Table taken from Effects of Snowmobile Use on Snowpack Chemistry in Yellowstone National Park
Click on the graph to see ammonium and sulfate concentrations on snowmobile routes.

What do you think?
  • According to the first graph, how is the distribution of n-alkanes and n-alkyl acids (an expected oxidation product of n-alkanes) in the snowpack related to proximity to roads used by snowmobiles?
  • According to the second graph, how is the concentration of ammonium and sulfates related to proximity to roads used by snowmobiles?
  • Based on this research, do you think this distribution can be definitively attributed to snowmobile emissions?
Map of Yellowstone, snowmobile route map. Details
Read about the Impact of Two-Stroke Engines on Aquatic Resources (Acrobat (PDF) 36kB Apr3 06) to learn about the potential impacts of snowmobile emissions on aquatic organisms. (The full report is available below.)
  • There are 185 miles of paved roads groomed for snowmobile use in park, most of which are adjacent to rivers, streams and ponds (see snowmobile route map at right). Considering what you have learned about the distribution of pollutants in the snowpack and the effects of toxins on aquatic organisms, do you think there is potential for surface water contamination from snowmelt runoff? Consider factors such as distance of contaminated snowpack from waterbody, contaminant level versus dilution factor (how large is the water body, is it contained or free-flowing?) and so on.

Impacts on Wildlife

Snowmobiles passing bison in Yellowstone National Park. Details

Many studies have looked at how wintertime stress affects animal health and survival, but measuring the added stress of vehicle proximity and noise emissions is problematic. Aside from observed interactions between snowmobiles and animals, it is difficult to determine what kinds of long-term impacts snowmobiles may have on animal health from sources such as toxins in snow, water, or soil and the bioaccumulation effects of eating plants that may have taken up these toxins. Furthermore, even highly specialized biochemical studies that look for stress levels in animals may not be able to distinguish the sources of that stress.

Review some of the research:
Fox in Lamar Canyon in Yellowstone National Park. Details
What do you think?
  • What is the most common reaction animals have to snowmobiles? Do different animals have different reactions?
  • Can stress hormone levels measured in fecal matter be definitively attributed to snowmobile activity? What else may cause elevated stress levels during winter?
  • Do these studies indicate that snowmobiles are a danger to wildlife?

Human Landscape Issues

Noise Level Impacts

Sunset in winter over Yellowstone Lake. Details

While hearing impairment and high blood pressure are notable health concerns related to sustained high-level noise pollution, when it comes to snowmobiling in the Park the issue is also about how noise emissions affect the visitor experience.

See what those in the snowmobiling industry have to say:
See what opponents of snowmobiles have to say:
What do you think?
  • Do noise emissions from snowmobiles have a negative effect on animals?
  • Do snowmobile sound levels cause health problems or are they more just a nuisance?

Economic Impacts

Cooke City at Northeast entrance to Yellowstone National Park. Details
Snowmobiling is a $27 billion industry in the United States, and the average snowmobiler spends $4,000 annually on recreation. Many small towns in the Park's border states of Idaho, Montana and Wyoming depend upon revenues earned during the winter season. For example, more than half of the 65,000 snowmobiles that entered Yellowstone in 2001 accessed the Park through the town of West Yellowstone, Montana accounting for 75% of Montana's total revenue from the snowmobile industry that year. Read about how winter use regulations and a Lack of Snowmobiles Affect Montana Town.

According to a 1998 report on the Economic Importance of the Winter Season to Park County, Wyoming, 30% of local businesses said that nearly 80% of their total winter revenues came from winter visitors to Yellowstone National Park. This table from the report (Acrobat (PDF) 9kB Apr13 06) shows the economic impact to Park Country of YNP visitors. The Wyoming Department of State Parks and Cultural Resources reports that a ban on snowmobiles could cost Wyoming as many as 938 jobs, no small layoff considering the total state population is just under 494,000. Read the article Yellowstone Snowmobile Ban Leaves Working Families in the Cold for more details.

However, there are hundreds of miles of National Forest open to snowmobiles directly outside Yellowstone, so a ban on snowmobiles in the Park would not mean and end to the snowmobile-based economy altogether.

Furthermore, some would argue that the relative economic health of border towns should not be considered a priority when determining how best to preserve the ecosystem health of a national park. As Kevin Collins of the National Parks Conservation Association says, "It is also essential to note that the mission of the National Park System is NOT to provide economic benefits to nearby communities and businesses. Having a national park nearby is an economic asset for which any community would be grateful. Nevertheless, this fortunate byproduct of the park's existence must not be allowed to dictate park management policy."

Some locals believe that a ban on snowmobiles may lead to an increase in snow coach travel and overall visitation due to improved conditions. They are adding snowcoach tours to replace lost snowmobile business. Read more about how Yellowstone Guides and Visitors Praise Snowmobile Phaseout's Positive Impact on Park Conditions.

Visit the West Yellowstone Chamber of Commerce's "White Season" and the Cody, Wyoming Chamber of Commerce's "Outdoor Recreation" to see how the snowmobile industry effects the local economy in these border towns.

What do you think?
  • How are small, tourism-dependent towns affected by restrictions on snowmobile use in the Park?
  • Are their other options, such as snow coaches or the hundreds of miles of National Forest trails outside the Park, which could mitigate the effects of lost revenue if snowmobiles are banned from the Park?
  • Do economic benefits to local communities outweigh conservation concerns?

Public Opinion


According to the SEIS, more than 90% of winter visitors in Wyoming would not consider taking a snowcoach instead of riding a snowmobile.


The original EIS, the SEIS, the Clinton administration, and an overwhelming number of public comments supported banning snowmobiles from Yellowstone.

Proposed Solutions and Alternatives

Snowmobiles led by a guide in Yellowstone National Park. Details
In 2004, the National Park Service reviewed five alternatives to current snowmobile regulations ranging from banning snowmobiles entirely to allowing snowmobile use according to daily entrance limits and guided tour requirements. Find out more about snowmobile regulation alternatives: As of winter 2006, restrictions on snowmobile use allow for 720 machines in the Park daily, but all riders must be accompanied by a certified guide. Additionally, all snowmobiles must meet the Best Available Technology standards.

A snowmobile's impact on the environment and the scenery can be significantly reduced by using ethanol-blended fuels and new engine technologies, particularly four-stroke engines. Studies in Europe have found that biomass-based lube oil can reduce CO, PM, and HC emissions. Find out more:

Clean snowmobile challenge. Details
In response to the threat of a ban on snowmobiles in national parks, the Society of Automotive Engineers started the Clean Snowmobile Challenge in 2000. This annual competition challenges student designers to modify a stock snowmobile to make it cleaner and quieter, while still maintaining performance standards and cost-effectiveness. Find out more about the Clean Snowmobile Challenge:

Snowcoach in the Hayden Valley of Yellowstone National Park. Details
Another proposed solution is to increase snowcoach travel in the Park and eventually phase out snowmobiles. Many local retailers are already modifying their businesses to include snowcoach tours as well as snowmobile rentals.
Yellowstone Expeditions provides a brief overview of the mechanics and benefits of snowcoach travel.

What would you do?

There is an obvious need for more research on this topic. What types of questions still need to be asked and what kinds of experimental design would be required to answer them?
Check out the Role-Play Activity for a way to use this module in the classroom.