Physical Landscape

North America is divided into several physical regions with distinct landforms. The western part of the continent is marked by north-south mountain ranges in the Rocky Mountains and Pacific Mountains and Valleys physiographic provinces, with the Intermontane Basins and Plateaus in between. The eastern portion of North America is defined by the ancient Appalachian Highlands, a mountain range that is much less rugged than the Rockies but with no less influence on the history and development of the United States. The interior of the continent is characterized by plains, the Interior Lowlands and the Great Plains. To the north is the Canadian Shield, geologically the oldest part of North America, and a sparsely populated area with poor soils. At the southern and eastern edge of the continent is the Gulf-Atlantic Coastal Plain, a relatively flat zone that extends from New York to Texas.

Traditionally, the continent of North America extends from the Canadian Arctic through the United States and Mexico to the narrow Isthmus of Panama. When considering the “region” of North America, however, that is, the area united by common physical and cultural characteristics, there are distinct similarities between Canada and the United States in terms of language and a shared history that are quite different from their Spanish-speaking neighbors to the south. Although the narrow strip of land that typically divides North and South America makes for an easy way to divide these two regions, in many ways, Middle America is mostly a transition zone between more powerful economies to the north and south. Mexico, for example, culturally resembles countries like Guatemala and Honduras to the south while physiographically, it resembles the southwestern United States. Thus, the United States and Canada are discussed in the North America chapter while Mexico and Central America are considered alongside the chapter on South America.

The physiographic regions of North America are well-defined and are commonly recognized by its residents. Someone might say he is from “Appalachia,” for example, or that she grew up in the “Rocky Mountains.” In general, the physiographic regions have a strong north-south alignment. Climatically, the region is quite diverse, ranging from tundra in northern Canada and Greenland to semi-arid desert in the southwestern United States. These diverse physical conditions have enabled North America to have a wide variety of natural resources, but have also contributed to significant regional differences.

Climate and Biomes

As with the physical landscape, the climate zones of North America are diverse. In general, North America has a relatively simple weather system. As you increase in latitude north, the temperature decreases, and as you travel west to east, the precipitation increases. Thus, California, on the west coast, is relatively warm and dry, while Florida on the east coast is hot and wet.

The climates of the United States and Canada include the frigid type E climate of the tundra of northern Canada and Alaska, the tropical type A climate of southern Florida and Hawaii, the type C climates of the humid eastern United States, the seasonal type D climates of the northern United States and most of Canada, and the arid type B climates of the Southwest and Great Plains. In general, there are two different climate patterns common in North America. The first pattern is that temperatures get warmer from north and south, towards the equator. The second pattern is that there is a decrease in precipitation as you move from east to west across the continent until you reach the Pacific Coast, where rainfall is abundant again.

The second climate pattern is created by the rain shadow effect of the western mountain ranges. As wet air masses move from the Pacific Ocean over the North American continent, they run into the Cascades and the Sierra Nevada. The Cascade ranges of Washington State and Oregon cut off moisture from falling on the leeward side of the mountains; thus eastern Washington State and eastern Oregon are semiarid. The western United States experiences a strong rain shadow effect. As the air rises to pass the mountains, water vapor condenses and is released as rain and snow. This means that west of these mountain ranges there is much more precipitation than to their east, resulting in arid and semiarid lands. The entire Great Plains of the western United States are affected by the rain shadow effect and have a semiarid type B climate.

The giant redwoods that stretch over California’s Redwood National Park are the tallest trees on Earth, towering to over 100 meters (328 feet). These trees are also ancient. One such tree, known as “General Sherman,” is the largest in the world by volume and is believed to be over 2,000 years old. At the time General Sherman first emerged from the ground, North America was settled by several indigenous groups. It would be 1,000 more years until Europeans would make contact with the Americas. Today, though many of the redwoods remain, both the physical and human landscape of North America have profoundly changed.

Most of Canada’s land area consists of the boreal forest, known as taiga in Russia. This boreal forest area consists of coniferous trees, such as spruce and pine, and is characterized by a cold climate. For Canada’s indigenous communities, in particular, this vast stretch of woodland has been a valuable resource. The rocky landscape of the Canadian Shield extends from the Arctic regions of Central Canada west through Quebec and is among the oldest geologic formations on Earth. It also has some of the world’s most abundant mineral areas.

Geology

Most of North America, to include Mexico, Greenland, and some of the Caribbean, is situated on the North American plate and is thus relatively geologically stable. One notable exception, however, is the Juan de Fuca Plate, which is subducting under the North American plate near California and Vancouver Island, an area known as the Cascadia subduction zone. Severe earthquakes, generating tsunamis, have occurred here roughly every 500 years; the last major earthquake in the area was in 1700 CE. Just to the south, the San Andreas Fault running along the edge of California forms the boundary between the Pacific Plate and the North American Plate. This is a transform plate boundary, with the two plates sliding past each other horizontally. San Francisco is located on this fault line, and the area has experienced numerous earthquakes.

Hydrology

North America has several significant rivers, some of which are used for shipping and others for hydroelectric power. The longest North American river is the Missouri, which forms in Montana and flows into the Mississippi River. The Mississippi River is primarily considered to be the most crucial waterway in terms of commercial transportation. The Port of South Louisiana, located along the Mississippi, is the largest port in the United States in terms of tonnage.

Below North America lies several aquifers, or underground layers of permeable rock that hold groundwater. The largest of these aquifers is the Ogallala Aquifer located in the central United States stretching from South Dakota down to Texas. This aquifer supplies water to much of the Great Plains, it supplies about one-third of all groundwater used for irrigation in the United States. While aquifers are beneficial for irrigation, they replenish their water supplies relatively slowly through rainfall. The depletion of the Ogallala Aquifer has accelerated over the past few decades, and currently, water is being taken out of the aquifer at a faster rate than it can be replaced. Once all of the water is depleted, it will take around 6,000 years to replenish naturally. Groundwater conservation initiatives in the area have aimed to slow the depletion rate by encouraging farmers to practice sustainable irrigation methods.

While farmers have been encouraged to conserve water, groundwater depletion is just one of the many environmental concerns currently facing North America’s farmers. Sustainable agriculture more broadly remains an important initiative. This type of agriculture looks at farming’s effect on the broader ecosystem and seeks to produce agriculture in a way that does not negatively impact the ecosystem in the long-term. It is essentially farming that can be sustained and seeks to minimize water use, soil erosion, and harmful chemicals. Globally, over one-third of all agricultural land has become degraded due to poor land and resource management. Soil is a finite resource, and topsoil can take over 500 years to form. Traditional forms of agriculture, where you might see vast stretches of tilled land, can often lead to topsoil erosion. Through sustainable agricultural practices, soil erosion rates have slowed in the United States over the past several decades.

Environmental Issues

Environmental Pollution

Many environmental problems like topsoil erosion and groundwater depletion affect a wide area and can have far-reaching effects beyond areas where the environment is not being sensitively managed. Acid rain, for example, formed from sulfur dioxide and nitrogen oxide emissions can have damaging effects far beyond the areas that are emitting these gases. When cars or factories burn fossil fuels, those nonrenewable sources of energy formed by the remains of decayed plants or animals, they release several chemicals including sulfur and nitrogen. These gases react with water in the atmosphere to form a highly acidic rain that can damage plants and animals. The lower the pH value, the more acidic a substance is; pure water has a pH of 7. Acid rain can have a pH of around 5.0, or even below 4.0 in some areas. Pickles, by comparison, have a pH of around 5.20, so imagine the devastating effects of this acidic precipitation on the environment. The strict regulation of fossil fuel emissions since the 1970s has dramatically reduced instances of acid rain in the United States, but some argue that further regulation is needed to address changes in global climate and other pollution concerns.

Anthropogenic Climate Change

More importantly than acid rain is the causes and potential consequences of anthropogenic climate change across North America. In 2017, the United States produced a scientific report titled Fourth National Climate Assessment, Volume I. Within that report, it focused on how climate will impact temperatures, water resources, sea-level rise, and other natural systems across the nation. More specifically, the report highlighted:

• Global and U.S. temperatures continue to rise
• Many temperature and precipitation extremes are becoming more common
• Oceans are rising, warming, and becoming more acidic
• Climate change in Alaska and across the Arctic continues to outpace global climate change
• Limiting global average warming to 2 degrees Celsius (3.6 degrees Fahrenheit) will require major reductions in fossil fuel emissions
• There is a significant possibility for unanticipated changes

In 2018, the U.S. government released the next volume of the Fourth National Climate Assessment, titled Volume II: Impacts, Risks, and Adaptation in the United States. Within that report, it highlights:

• Communities: Climate change creates new risks and exacerbates existing vulnerabilities in communities across the United States, presenting growing challenges to human health and safety, quality of life, and the rate of economic growth.
• Economy: Without substantial and sustained global mitigation and regional adaptation efforts, climate change is expected to cause growing losses to American infrastructure and property and impede the rate of economic growth over this century.
• Interconnected Impacts: Climate change affects the natural, built, and social systems we rely on individually and through their connections to one another. These interconnected systems are increasingly vulnerable to cascading impacts that are often difficult to predict, threatening essential services within and beyond the Nation’s borders.
• Actions to Reduce Risks: Communities, governments, and businesses are working to reduce the risks from and costs associated with climate change by taking action to lower greenhouse gas emissions and implement adaptation strategies. While mitigation and adaptation efforts have expanded substantially in the last four years, they do not yet approach the scale considered necessary to avoid substantial damages to the economy, environment, and human health over the coming decades.
• Water: The quality and quantity of water available for use by people and ecosystems across the country are being affected by climate change, increasing risks and costs to agriculture, energy production, industry, recreation, and the environment. 
• Health: Impacts from climate change on extreme weather and climate-related events, air quality, and the transmission of disease through insects and pests, food, and water increasingly threaten the health and well-being of the American people, particularly populations that are already vulnerable.
• Indigenous Peoples: Climate change increasingly threatens Indigenous communities’ livelihoods, economies, health, and cultural identities by disrupting interconnected social, physical, and ecological systems.
• Ecosystems and Services: Ecosystems and the benefits they provide to society are being altered by climate change, and these impacts are projected to continue. Without substantial and sustained reductions in global greenhouse gas emissions, transformative impacts on some ecosystems will occur; some coral reefs and sea ice ecosystems are already experiencing such transformational changes.
• Agriculture: Rising temperatures, extreme heat, drought, wildfire on rangelands, and heavy downpours are expected to increasingly disrupt agricultural productivity in the United States. Expected increases in challenges to livestock health, declines in crop yields and quality, and changes in extreme events in the United States and abroad threaten rural livelihoods, sustainable food security, and price stability.
• Infrastructure: Our Nation’s aging and deteriorating infrastructure are further stressed by increases in heavy precipitation events, coastal flooding, heat, wildfires, and other extreme events, as well as changes to average precipitation and temperature. Without adaptation, climate change will continue to degrade infrastructure performance over the rest of the century, with the potential for cascading impacts that threaten our economy, national security, essential services, and health and well-being.
• Oceans and Coasts: Coastal communities and the ecosystems that support them are increasingly threatened by the impacts of climate change. Without significant reductions in global greenhouse gas emissions and regional adaptation measures, many coastal regions will be transformed by the latter part of this century, with impacts affecting other regions and sectors. Even in a future with lower greenhouse gas emissions, many communities are expected to suffer financial impacts as chronic high-tide flooding leads to higher costs and lower property values.
• Tourism and Recreation: Outdoor recreation, tourist economies, and quality of life are reliant on benefits provided by our natural environment that will be degraded by the impacts of climate change in many ways.