"....to conserve the scenery and the natural and historic objects and the wild life therein and to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations." – The Organic Act of 1916, which established the National Park Service
What does it mean to conserve and protect a place during a time of large-scale environmental change?
Yosemite’s climate is changing. While changes in weather take place over minutes, hours, or days, changes in climate are measured over years, decades, or centuries. Weather data have been collected in Yosemite since 1895, giving us a window into long-term shifts in the park’s climate:
Rising temperatures: Over the period 1895–2016, the total area within park boundaries warmed at a rate of 1.6°F per century. That rate more than doubled in more recent decades; over 1950–2010, Yosemite warmed at the rate of 3.4°F per century.
Higher lows: Nighttime minimums measured in Yosemite Valley have risen faster than average temperatures, increasing by 7.6°F over 1915–2012.
Longer growing season: By 2012, Yosemite Valley was experiencing around 88 more frost-free days than it was in 1907.
These local patterns reflect larger shifts in the world’s climate. While Earth does go through natural warming and cooling cycles lasting tens of thousands of years, evidence shows that we are currently in a natural cooling period. The vast majority of scientists agree that recent changes in Earth’s climate are caused by human-produced greenhouse gases that trap heat close to the planet’s surface. Like a sleeping bag on a cold night, natural greenhouse gases perform the essential function of trapping enough heat in the atmosphere to support life on Earth. However, fossil fuel burning, deforestation, and large-scale farming have produced historically high levels of carbon dioxide, methane, and other greenhouse gases in the atmosphere—carbon dioxide levels today are at their highest in three million years. Without a major reduction in global greenhouse gas emissions, scientists project the following trends in Yosemite’s climate over the next century:
Faster warming: Average temperatures in the park may rise by 6.7–10.3°F between 2000 and 2100.
More hot days: Days per year with temperatures above 90°F may quadruple from around 12 in 2016 to 48 by 2100 (days above 100°F may jump from 1 to 13).
Extreme weather: Average precipitation may not change significantly, but central California is likely to experience extreme storms more frequently (storms that historically broke 20-year precipitation records may occur every five–six years).
Climate change is already altering Yosemite’s ecosystems and the experience of visiting the park—but projecting the impacts of these changes is a complex science. Some natural cycles like wildfire, seasonally dry waterfalls, and tree death already take place but are exacerbated by climate change. Small shifts can set off domino effects; for instance, warming temperatures melt snow in the mountains and expose darker-colored ground that in turn absorbs more heat, leading to more snowmelt. Still other changes are driven by complex interactions between climate and fire management practices, natural drought, animal behavior, invasive species, and human use of the park. By studying the shifts we are already seeing in Yosemite, we can better understand the meaning of conservation in a time of change.
Climate change may impact hikers, backpackers, and sightseers as summers heat up, high-elevation streams dry, and smoke becomes more common.
National parks take on new roles in a time of large-scale change. They provide refuge to threatened species, protect critical water supplies, and serve as outdoor laboratories for scientists to study changes and impacts. They are also centers of teaching and learning, where millions of people come together to connect with the natural world, our history, and each other.
Although climate change presents local challenges, it is a global issue. No one person, park, or country can manage its impacts alone. Many visitors leave the park inspired by Yosemite’s iconic waterfalls, vistas, and wildlife, but our ability to conserve, protect, and teach doesn’t end at the park boundaries. What changes are taking place in your neighborhood, state, or country? As we continue to share the unfolding stories of climate change, what part will you play?