Earth's Resources, Hazards and Human Impact

Renewable vs. nonrenewable resources

In plain words: renewable means nature refills it fast. Think of a paycheck that comes every week versus savings that can run out.

The key question is how fast nature replaces the resource. It does not matter whether it is clean or cheap.

Watch for these two traps:

1. Nuclear power is nonrenewable. It gives off almost no carbon dioxide while running. But its fuel, uranium, is mined and will not be replaced.
2. Some "renewables" can be used up locally. Trees, fish, soil and groundwater are renewable only if we use them slowly enough. We must not take them faster than they are replaced. Cut a forest faster than it regrows, or pump an aquifer faster than rain refills it, and the resource shrinks.

Trade-offs. Fossil fuels are reliable but release carbon dioxide and air pollutants. Wind and solar are clean but work only when the wind blows or the Sun shines. Dams give steady power but block fish migration.

Natural hazards and how people reduce harm

In plain words: we can't stop storms or earthquakes, but we can get ready for them.

A storm over an empty ocean hurts no one. A natural hazard becomes a disaster when it meets people and property. Scientists cannot stop hazards. But they can predict them, prepare for them, and mitigate them — make the harm smaller.

Hurricanes in detail. The Saffir-Simpson scale ranks hurricanes from Category 1 (74–95 mph) to Category 5 (157 mph or more) by sustained wind. But the category describes only wind. Storm surge and rain flooding often cause more deaths. Hurricanes weaken over land or cold water because they lose their fuel: warm, moist air.

Human choices change risk. Building on floodplains or coastlines raises exposure. Paving over land increases runoff and flooding. Draining wetlands removes a natural sponge. Many GED questions ask which action would best reduce a specific hazard. So match the fix to the danger. Shutters stop wind damage, not floodwater.

Human impact and pollution

In plain words: what people put into the air, water and land comes back to affect us.

People change every part of the Earth system.

Air. Burning fossil fuels releases carbon dioxide. It is a greenhouse gas — a gas that traps heat, like a blanket — and it drives climate change. Burning also releases soot, sulfur dioxide and nitrogen oxides. Sulfur and nitrogen oxides form acid rain, which harms lakes and forests. Car exhaust and sunlight form ground-level ozone (smog), which irritates lungs. Note: ozone high in the stratosphere is helpful because it blocks ultraviolet light. Ozone at ground level is a pollutant.

Water. Fertilizer runoff causes eutrophication. The chain goes: extra nitrate and phosphate → algae bloom → algae die → bacteria decompose them and use up oxygen → fish suffocate (a "dead zone"). Sewage, oil spills, industrial chemicals and plastic trash also pollute water. Some toxins, such as mercury, build up in organisms and become more concentrated higher in the food chain.

Land. Clearing forests for farms and cities causes habitat loss and soil erosion, and it reduces biodiversity. Landfills and mining can leak chemicals into groundwater.

Solutions include:

• the "three R's" (reduce, reuse, recycle);
• switching to renewable energy;
• buffer strips of plants along streams to trap runoff;
• emission limits, protected habitats, and fishing quotas.

Sustainability: judging resource use from data

In plain words: it works like a bank account. If you spend more than you put in, the balance shrinks.

A resource is used sustainably when the amount taken is no more than the amount replaced. You can test this with simple numbers:

• Compare inputs and outputs. If an aquifer gains 2.0 km³ a year from rain and loses 3.0 km³ to pumping, it shrinks by 1.0 km³ a year.
• Find the break-even point. If a fish population adds 15% each year, catching more than 15% each year makes it shrink.
• Read trends carefully. A water table depth that increases means the water level is falling. Always read axis labels.
• Use percent change correctly. Percent change = \dfrac{\text{new} - \text{old}}{\text{old}} \times 100\%. A change in a share, such as from 45% to 18%, is a change of 27 percentage points. That is not the same as a 27% change.

The GED often pairs a data display with a claim, such as "the lake is polluted because of the factory." Then it asks which evidence supports or weakens the claim. Good evidence shows that the suspected cause changed when the effect changed. The best evidence also has a control — a site or group without the suspected cause, used for comparison.