Climate Change in U.S. National Parks

The National Parks system in the United States has often been referred to as "America's Best Idea". Pioneered by John Muir in the late 18th century, the U.S. National Parks system encompasses and protects the most beautiful parts of the United States. The National Parks System maintains and protects more than 85 million acres in all 50 states.

Unfortunately, National Parks have been heavily affected by anthropogenic-induced climate change, much like the rest of the United States and the rest of the planet. Since 1895, the U.S. National Park System has seen greater increases in heat and aridity than the country as a whole because extensive areas of the National Park System are located in extreme environments in Alaska and the American West.

Between 1895 and 2010, the mean annual temperature of the national park area increased at double the rate of the US as a whole. Seasonally, winter, spring, and summer showed similar rates of increase for the national park area, while the greatest temperature increase for the U.S. occurred in winter. Additionally, a greater fraction of the national park area (63%) experienced significant temperature increases than the US as a whole (42%) (Gonzalez et al. 2018).

Annual precipitation increased significantly in the US as a whole while annual precipitation in the national park area decreased, although the change was not statistically significant (Gonzalez et al. 2018).

The IPCC (International Panel on Climate Change) has identified major climate scenarios based on global emissions referred to as RCPs (Representative Concentration Pathways). Here the most common four RCPs are examined. RCP 2.6 is reliant on CO2 emissions starting to decline in 2020 and would result in global warming below 2°C by 2100. RCP 4.5 is reliant on emissions sharply declining after 2040 and would result in warming between 2°C and 3°C. RCP 6 is reliant on emissions declining after 2080 and would result in warming between 3°C and 4°C. Finally, RCP 8.5 is reliant on CO2 emissions continuing to rise by 2100 and would result in warming between 3°C and 5°C. With business as usual, RCP 8.5 is the path we are on.

The only way to avoid warming reaching RCP8.5 levels, drastic measures to reduce carbon emissions will be necessary. The vast majority of the global population relies on fossil fuels and natural gas so the first major step towards reducing emissions will rely on a green zero carbon emission infrastructure. Every nation has control over their own infrastructure and climate policy, which makes coming to a consensus decision much more difficult. There is no "one size fits all" climate policy that can be set in place to reduce carbon emissions.

Yosemite National Park in California is one of the Nation's Oldest Parks and is often the place credited with creating the National Parks System. Yosemite National Park was established on October 1, 1890, but has been preserved since President Lincoln signed the Yosemite Land Grant on June 30, 1864, protecting the Mariposa Grove and Yosemite Valley. Although conservation and stewardship have protected Yosemite in the past, there is no clear way to protect the park from climate change. Yosemite National Park has already been affected by climate change in many ways including shifting ecosystems, decreased snowpack, increased fire activity, and much more.

Yosemite National Park is the 16th largest National Park in the United States covering more than 750,000 acres of land in the Sierra Nevada Mountains. The park sits in four counties: Tuolumne, Mariposa, Mono, and Madera (Data: NPS Open Data Portal).

Alpine chipmunks have lost 60% of their range on the west slope of the Sierra Nevada Mountains. They were once found as low as 7,800 feet, but they are now only seen above 9,800 feet. The chipmunk's genetic diversity has fallen as its range has contracted, making the species less resilient to future changes (NPS 2020). Alpine chipmunks are just one example of a species whose range has been greatly reduced due to warming.

Throughout the Sierra Nevada, April 1 snowpack is decreasing at elevations below 8,500 feet but increasing slightly at higher elevations. This pattern is reflected inside Yosemite, where low-elevation snow surveys show that snowpack in the heaviest years is decreasing over time, while no trend appears at higher elevations (NPS 2020).

Yosemite has also seen a large increase in fire activity each summer. Past years have seen longer wildfire seasons and fires with larger and larger burn areas. Pictured on the left is an image of the 2022 Washburn Fire in Yosemite's famed Mariposa Grove. The grove is home to more than 500 mature Sequoia trees, some of the oldest and tallest trees on planet earth. An increase in fire mitigation tactics ended up keeping the vast majority of the grove safe, but the odds of losing these great Sequoias increase each year.

Under RCP2.6, 58% of national park area would experience a mean annual temperature increase >2°C from 2000 to 2100. This increase under 2°C is at the upper limit of the Paris Climate Accord and would require a substantial reduction in carbon emissions globally. Under RCP2.6, the fraction of the national park area located in areas of >2°C increase would be double the fraction for the US as a whole, indicating a disproportionate exposure of national park area. A majority of the national park area and most individual national parks would be located in areas of >2 °C increase under all four emissions scenarios (Gonzalez et al. 2018).

With continued greenhouse gas emissions, projected rates of 21st-century temperature increase under the highest emissions scenario (RCP8.5) would be six times greater than 20th-century rates for the national park area and the U.S. Under RCP8.5, 100% of the national park area would experience a mean annual temperature increase >2°C from 2000 to 2100. This would put 100% of national park area above the 2°C threshold set by the Paris Climate accord (Gonzalez et al. 2018).

More fires. Models project a 19% increase in the number of annual fires from 2020-2049 in Yosemite, leading to a proportionate increase in the annual area burned (NPS 2020).

Dramatic snowpack loss. The total annual snowpack in the Merced River basin may decline by 49% and across the Sierra Nevada, snowpack is likely to decline by 64%. Melting in the Merced River basin may also arrive around one month earlier (NPS 2020).

Non-native plants and animals could become more common while eliminating native ones. The lower edge of the conifer forest may creep upward from its current elevation of 3,000 feet, transforming low-lying areas of the park from pine-cedar forests into oak-chaparral scrubland. And, increasing fire activity may lead to permanent ecosystem turnover, as changing conditions prevent historically present species from returning to burned areas.

Different climate scenarios paint different pictures of an anthropogenic-induced warmer future. The only certainty is that the planet will continue to warm. Without drastic measures being taken in the coming decades, past warming trends indicate more than 3°C by 2100 throughout the continental United States, with national park areas predicted to warm more than 5°C. Climate Change will not only impact the outdoors, but will begin to have a large impact on day to day life. Water will become more expensive. Heating and air conditioning will become more expensive. Gas will become more expensive. Food will become more expensive, and so on. As the planet continues to warm, climate change will affect more facets of everyday life and will begin to affect every corner of the world. The future is uncertain. Not if the planet will warm, but rather how much will it warm.