From widespread wildfire smoke to rising flood waters, and Alaskan heat waves to freezing temperatures in Texas, few communities haven't felt the effects of a changing climate. In particular, those who live in high elevation regions or depend on mountain ranges for fresh water may have a distinct perspective on climate change; for some researchers, mountains are considered climate “hotspots” that anticipate or amplify climate change impacts that occur at lower altitudes. Read on to explore a few of the environmental, ecological, and societal impacts of global climate change across mountain ranges—and to understand how the geographic features of mountainous regions affect and are affected by extreme weather.
How mountains affect precipitation
Mountain ranges have a major influence on the amount of precipitation that occurs on each side of a mountain—and whether it comes in the form of rainfall, ice, or snow. In scientific terms, these phenomena are referred to as the orographic effect and rain shadow.
The orographic effect
The orographic effect occurs when air masses are forced higher over mountains and form clouds that induce precipitation. As the air moves upward, its temperature decreases, and the air condenses to form clouds. Once these clouds can no longer hold any more moisture, they release precipitation, such as thunderstorms or snowstorms. The orographic effect occurs on the windward side of the mountain and results in a climate that includes heavy rainfall and lush green vegetation. Examples of areas that experience this effect include the Appalachian Mountains of West Virginia and the eastern seaboard of Australia.
Rain shadow
Rain shadow refers to an area of land on the leeward side of a mountain that experiences significantly less rainfall than the windward side. It occurs when dry, warm air travels over a mountain peak, which impedes cloud formation and results in desert-like conditions. A well-known example is Death Valley, between the Sierra Nevada and Pacific coast mountain ranges, which is one of the warmest and driest places on Earth. The Tibetan Plateau of the Himalayas is another prominent rain shadow, impacting multiple countries.
The connection between mountains, altitude, and temperature
Altitude refers to the distance above sea level, with areas at 8,000 feet or more generally considered to be high-altitude. At over 29,000 feet, Mount Everest is the point of highest altitude above sea level on Earth. High-altitude areas typically experience cooler temperatures, more precipitation, strong winds, and low air pressure and oxygen levels. Lower altitude areas are often characterized by warmer temperatures, little precipitation, less wind, and higher air pressure and oxygen levels.
Elevation-dependent warming
Elevation-dependent warming (EDW) refers to differential rates of warming dependent on a mountain’s height above sea level. As you move up a slope, vegetation and landscape tend to transition from farmland to forests, meadows, and, eventually, ice and snow. These different zones may also react to warming at different rates. For instance, melting ice can enhance warming as highly reflective snow is replaced with the dark soil underneath; however, this effect only occurs in areas where snow already exists, so it’s more prevalent at the poles or mid-latitudes.
How mountains respond to climate change
A recent study by geoscientist Jasper Knight of the University of Witwatersrand in Johannesburg found that mountain ranges respond in variable and complex ways to climate change—and that mountains with snow and ice function differently than those at low latitudes. Knight highlights the interconnectivity between the different spheres of sensitivity for a mountain environment. For example, mountain snow, ice, and glaciers are important sources for fresh water around the globe; snowpack can help protect mountain peaks from warming, but are also vulnerable to rapid melting as global temperatures increase. Mountain river systems feed delicate alpine ecosystems of rare plant and animal species; overflowing with snowmelt, they can endanger those ecosystems with floods and mudflows. Those hazards pose risks for human infrastructure—mines, communities, important sites for cultural heritage and protected landscapes—which, in turn, can accelerate erosion and temperature change.
Climate change in mountain ranges over the last century
In an article published in Reviews of Geophysics, the authors discussed how the effects of global warming and climate change are often intensified in higher mountain ranges. Since solid record-keeping began in 1950, mountains have been warming about 25 to 50% faster than the global mean, and there is increasing evidence that precipitation is not as high as it has been historically. According to the authors, this means that although precipitation is increasing in many mountain areas, the rate isn’t as fast as would be anticipated given the rising temperatures. Additionally, not only are nearly all mountain glaciers receding at an accelerating rate, but climate zones have also migrated upslope in a manner that is unsustainable for many species, potentially resulting in mass extinction.
Climate change by mountain region
How mountains affect climate around the world varies by location. This makes sense given that mountain ranges, such as Kilimanjaro of East Africa or the Andes of South America, are located in tropical zones, while the Alps, Himalayas, and the Denali of Alaska have vastly different climates. According to an Eos interview with the above-mentioned authors, increased warming via the melting and retreating of snow is now less pertinent in tropical mountains like Kilimanjaro because there are so few glaciers left. Climate change in the Andes varies substantially between the eastern and western slopes because moisture changes from the Amazon basin affect the former, and the Pacific Ocean influences the latter. Longer mountain ranges like the Rockies and Andes function as barriers, which means that different climate change impacts are felt on each side.
How human life is impacted by changing mountain climates
Even if you don’t live in a mountainous region, you may still depend on a distant range for resources and services. Below are three examples of how communities may be impacted by elevation-dependent warming.
Water supply
Mountains serve as water towers by redirecting air masses upwards, where they cool and eventually fall as rain or snow. 1.9 billion people living in or directly downstream from high mountain ranges—such as the Himalayas of India and China—rely on the water supply from gradually melting snow for drinking water and to prevent extreme drought. As global warming melts mountain glaciers at faster rates, bushfires could become more prevalent in these mountain forests that experience less winter snow and in dry climates such as those surrounding the Sierra Nevada Mountains in the western United States.
Energy sources
In many areas of the world, hydroelectric power is a necessity. For example, cloud forests that form in the high-altitude tropical mountain ranges of South America catch rainfall and fogs, so they reach surrounding rivers that flow to hydro dams downstream that power major Brazilian cities, including Sao Paulo and Rio de Janeiro. Cloud forests also filter sediment that flows in the water, which helps to prolong the efficacy of the dams. The effects of changing weather patterns in these mountain ecosystems could reduce rainfall and threaten power not only in Brazil but in other communities, cities, and countries around the globe.
Economic consequences
As a result of global warming and water scarcity, many traditional grazing areas for livestock are shrinking, endangering the livelihoods of farmers in mountain communities. Indonesia is one of the world’s largest coffee producers in the world due to the unique climate created by the surrounding mountains, but drier conditions and deforestation compromise the growth of this valuable crop. And for Nepalese and Tibetan people whose incomes rely on climbers at Mount Everest, increasing temperatures could impact tourism and threaten lives as the prevalence of avalanches and glacial outburst floods increases.
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Sources
https://sciencestruck.com/orographic-effect
https://education.nationalgeographic.org/resource/altitude/
https://ownyourweather.com/how-does-altitude-affect-climate/
https://eos.org/editors-vox/mountains-undergo-enhanced-impacts-of-climate-change
https://phys.org/news/2022-11-climate-impact-mountains-global-scale.html
https://www.conservation.org/blog/5-things-you-might-not-know-about-mountains-and-climate-change
