Human Impact

For most of Earth's history, rivers, glaciers, and volcanoes did the reshaping. Now there's a new force: people. With over 8 billion of us, humans move more rock and soil each year than all the world's rivers combined. Some scientists have even proposed naming a new time period after us, the Anthropocene ("age of humans").

That's not all bad news. Humans also clean up rivers, protect wildlife, and invent smarter ways to live. This chapter is about both sides.

It took all of human history until about 1804 to reach 1 billion people. Now we're over 8 billion. More people means more demand for food, water, energy, and land. The total impact depends on three things: how many people there are, how much each person uses, and the technology used to make it.

Your ecological footprint is the amount of land and resources needed to support your lifestyle: food, energy, housing, travel, and stuff you buy.

Air pollution comes from burning fuels in cars, factories, and power plants, plus natural sources like wildfires and volcanoes.

• Smog: a brownish haze formed when sunlight cooks car exhaust and other pollutants. It contains ground-level ozone, which hurts your lungs. (Ozone way up in the stratosphere is good. Down here, it's bad.)
• Particulate matter: tiny particles of soot, dust, and smoke that get deep into lungs. Wildfire smoke can make Idaho's air some of the worst in the country on bad days.
• Acid rain: sulfur dioxide and nitrogen oxides from burning coal mix with water to form acids, which damage forests, lakes, and buildings.
• Temperature inversions in Idaho's valleys can trap pollution near the ground for days in winter.

The Air Quality Index (AQI) tells you how safe the air is each day. The Clean Air Act (1970) has cut many major air pollutants in the U.S. dramatically.

• Point-source pollution comes from one clear spot, like a factory pipe or sewage plant. Easy to find and regulate.
• Nonpoint-source pollution comes from lots of spread-out places, like fertilizer washing off farms, oil from parking lots, and pet waste. It's harder to control and is now the biggest cause of water pollution in the U.S.

Extra fertilizer in water causes eutrophication: algae grow out of control, then die and rot, using up the oxygen and suffocating fish. Some of Idaho's reservoirs get toxic algae blooms in hot summers.

The Clean Water Act (1972) helped clean up many rivers. Idaho's Silver Valley shows how long cleanup can take: a century of mining left heavy metals like lead in the Coeur d'Alene River, and cleanup has been going on for decades.

• Deforestation: clearing forests for farms, cities, or lumber. Trees absorb CO₂, hold soil in place, and provide habitat, so losing them causes erosion and habitat loss.
• Urbanization: cities spreading into farmland and wild land. Idaho is one of the fastest-growing states, and the Boise area keeps expanding.
• Desertification: when overgrazing, drought, and poor farming turn dry land into desert.
• Soil erosion: remember the Dust Bowl from Chapter 8?
• Solid waste: the average American makes about 4.9 pounds of trash a day. Most goes to landfills. Plastic can last hundreds of years and breaks into tiny microplastics, now found everywhere from mountaintops to inside fish.

Biodiversity is the variety of life in an area. Healthy ecosystems with lots of species are more stable and give us food, medicine, clean water, and pollination.

Threats include habitat loss, pollution, overhunting and overfishing, climate change, and invasive species, plants or animals brought to a new place where they spread out of control. In Idaho, cheatgrass is an invasive grass that dries out early and fuels huge, fast-spreading range fires.

Idaho example: wild salmon used to return to Idaho by the millions, swimming over 900 miles from the Pacific. Dams, habitat changes, and ocean conditions have reduced their numbers, and people disagree about the best solutions, from fish ladders to hatcheries to removing dams.

As more people build in risky places, natural hazards cause more damage. Building homes in forests increases wildfire risk (the wildland-urban interface). Building on floodplains increases flood damage. Smart planning, such as hazard maps, building codes, and zoning, can save lives.

People are working on problems from many angles:

• Technology: cleaner engines, scrubbers on smokestacks, renewable energy, better batteries.
• Laws and policy: the Clean Air Act, Clean Water Act, Endangered Species Act, and the Montreal Protocol, which is healing the ozone layer.
• Conservation: national parks, wildlife refuges, and protected areas like Idaho's Frank Church Wilderness, the largest contiguous wilderness in the lower 48 states.
• Restoration: replanting forests, restoring wetlands, cleaning rivers, reintroducing species. Wolves were reintroduced to central Idaho in 1995.
• Individual choices: reducing waste, conserving water and energy, and learning the science so you can vote and decide wisely.

Every solution has costs and benefits, and reasonable people often disagree about which trade-offs are worth it. Good decisions come from good evidence.