Population Growth, Resource Debates, and Environmental Policy – Comprehensive Notes

Global human population surpassed 8 billion in 2023 and is still rising.
- Net annual addition ≈ 88 million people → ~2.8 persons s⁻¹.
- Real-time population counters: U.S. Census PopClock; visualization link provided in lecture.
United Nations 2100 projections (dependent on fertility scenarios):
- High: 15.6 billion
- Medium: 10.9 billion (most cited)
- Low: 7.3 billion
Historical milestones (billions reached): 1800 = 1, 1930 = 2, 1960 = 3, 1974 = 4, 1987 = 5, 1999 = 6, 2011 = 7, 2023 = 8.

Agricultural Revolution (∼10 000–8000 BCE)
- Shift from nomadic hunter-gatherers ➜ settled farming communities.
- Increased food production → better nutrition → lower death rates.
- Need for farm labor → higher birth rates.
- Population climbed to ≈100 million, then plateaued for centuries.
Industrial Revolution (≈1750 CE onward)
- Technological & energy breakthroughs: steam, coal, petroleum, dams, electricity.
- Transportation innovations: railroads, automobiles.
- Factory & assembly-line production, textile industry, Haber–Bosch ammonia synthesis.
- Haber–Bosch made $NH<em>3$ from $N</em>2$ and $H_2$ → nitrogen fertilizer → dramatic yield gains.
- Public-health advances (sanitation, medicine) → falling mortality; life expectancy more than doubled since 1800.

Exponential model (no limiting resources): $\frac{dN}{dt}=rN$
Logistic (density-dependent) model with carrying capacity $K$ :
$\frac{dN}{dt}=rN\left(1-\frac{N}{K}\right)$
Key question: Does human population ultimately face a planetary $K$ ? Resources, technology, and consumption patterns complicate simple ecological analogies.

Thomas Malthus (1798): food grows linearly while population grows exponentially → inevitable famine & poverty.
20ᵗʰ-century camps:
1. Neo-Malthusians (e.g., Paul Ehrlich, ecologist) – population growth causes scarcity & environmental degradation.
2. Cornucopians (e.g., Julian Simon, economist) – human ingenuity expands resource base; people are “the ultimate resource.”

Stakes: $\$1,000$ (inflation-adjusted) on the 1990 prices of five finite metals: chromium, copper, nickel, tin, tungsten.
Ehrlich prediction: prices rise (scarcity); Simon: prices fall or stay flat (innovation/substitution).
Outcome: All five metals fell in real price (up to −60 %); Simon won.
Follow-up debate:
- Was 10 years long enough to represent the “long run”?
- Metals may not capture broader environmental costs.
- A proposed second bet on 15 eco-metrics (pollution, soils, etc.)—11/15 trended as Ehrlich expected; Simon declined.
Contemporary consensus: resource distribution & access often matter more for human well-being than absolute scarcity.

≈60 % of humanity live in 10 countries; India overtook China as #1 in 2023.
Vital rates within a population:
- Birth rate (per 1 000 pop yr⁻¹)
- Death rate (per 1 000 pop yr⁻¹)
- Immigration (in-flow) & emigration (out-flow)
Demography = statistical study of population structure & change.
- Growth factors: clean water, nutrition, shelter, security.
- Resistance factors: disease, famine, war.
Crude birth rate variability (2020): ~10.6 (high-income) vs 20.1 (low-income) per 1 000.
Crude death rate less variable: global mean 7.5; low-income 7.0; high-income 10.2 (older populations).

Desired fertility reflects health, education, culture, religion, & economics.
Total Fertility Rate (TFR): avg. children per woman; 2019 global TFR = 2.5, highly uneven.
Pronatalist pressures increase TFR; antinatalist (education, contraception) lower it.
GDP vs Well-Being:
- GDP correlates loosely with TFR but is only production-based.
- Example analogy: post-hurricane rebuilding spikes GDP but not welfare.
Alternative indices:
- Human Development Index (HDI): life expectancy, education, income.
- Higher HDI → lower TFR; Kerala (India) cited as “HDI-driven demographic transition.”
- Gross National Happiness (GNH) – Bhutan’s multidimensional metric; faces emigration & job challenges.

More years of female schooling →
- Greater use/demand for contraception.
- Later marriage & delayed first birth.
- Labor-force participation & higher earnings → lower child mortality → smaller desired families.
Empirical observation: “As women become more educated, population growth slows.”

Carrying capacity ( $K$ ): max sustainable population given resource supply & per-capita consumption.
Overpopulation occurs when N>K locally or globally.
Ecological footprint: biologically productive land & water needed to supply resources + assimilate wastes for an individual/population.
- Larger footprint per capita → lower regional $K$ .

O₃ layer shields Earth from UV-B; loss means ↑ skin cancer, crop damage, phytoplankton decline, ecosystem disruption.
Cause: reactive chlorine from chlorofluorocarbons (CFCs); Antarctic vortex provides high radiation & PSC ice crystals that catalyze reactions.
Global response: 1987 Montreal Protocol phased out CFCs before all science was settled; a precautionary approach.
Climate-change parallels & contrasts:
- Both global, scientifically evident, anthropogenic.
- Ozone fix relatively simple (substitute chemicals); climate change entwined with energy, equity, regional winners/losers.
- Temporal dynamics: ozone hole appeared suddenly; climate warming gradual.
- Lobbying/policy complexity greater for fossil fuels than refrigerator coolants.

“Waste” is anthropogenic; natural systems cycle all matter.
Decomposers/detritivores (fungi, bacteria, worms, archaea):
- Aerobic decay → fast, odorless, $CO_2$ .
- Anaerobic decay → slow, odorous, $CH_4$ .

Engineered layers: soil cap, plastic liner, compacted clay, gravel, leachate pipes.
Anaerobic conditions suppress decomposition; produce landfill gas (~50 % $CH_4$ ).
Landfills are major anthropogenic methane sources.
- 500 / 2 600 EPA-tracked U.S. landfills capture & burn/use methane; 3 of top-10 emitters near Orlando, FL.

Hazardous = toxic, flammable, corrosive, explosive, radioactive.
- Common household items: paints, batteries, CFL bulbs.
E-waste contains rare-earth & precious metals + toxics; improper disposal → environmental & health harms; mining replacement metals damages ecosystems.

Controlled aerobic decomposition of organic waste → humus-like mulch.
Benefits: diverts biodegradable waste, enriches soil, mimics nature’s nutrient cycling.
Basic recipe (home scale):
- “Browns” (C-rich): dry leaves, straw, paper, wood chips.
- “Greens” (N-rich): grass clippings, food scraps, manure, tea bags.
- Avoid: meat, bones, oils, pet feces (odor, pests, pathogens).
Process requirements: oxygen (turn pile), water, proper C:N ratio; completion in weeks (home) to days (industrial).
Upcoming lab: compare decomposition rates (cherry plums, garlic clove, green tea bag) in two soil types.

Read textbook sections 6.1, 6.2, 7.1 before 24 Jul 2025.
Complete quiz on section 6.2.
Future lectures will revisit resource consumption, environmental policy, and sustainable materials management.