Global Environmental Change, Biodiversity Crisis & Conservation – Detailed Lecture Notes

Global, System-Level Assessments (Millennium Ecosystem Assessment, 2005)

• Interviewed $1{,}300$ experts from $95$ countries.

• Overarching conclusion: humans have disrupted $\approx 60\%$ of Earth’s life-support systems.- Impaired ability to meet human needs for food, water, timber, fuel.

  • Population still rising while carrying capacity is now falling.

• Social takeaway: no societal problem (poverty, migration, inequality) can be solved if environmental degradation continues.

Major Planetary Stressors Identified

• Loss of biodiversity → collapse of life-support services.

• HIPPO mnemonic (drivers of diversity loss):

1. Habitat destruction / fragmentation

   2. Invasive species

   3. Pollution

   4. Population (human over-population/over-consumption)

   5. Over-exploitation (hunting, fishing, logging)

• Global-scale phenomena beyond local insults:- Climate change

  • Stratospheric ozone depletion

  • Planet-wide contamination by synthetic chemicals & heavy metals

  • Homogenisation of ecosystems (same few tolerant species everywhere)

Disrupted Biogeochemical Cycles

Disruption of the Hydrologic Cycle and Related Impacts

• Cycle Disruption

  • Human activities (e.g., excessive groundwater extraction, land-use changes) have disturbed the natural water cycle.

  • Resulting consequences include:

  • Desertification: Productive land → desert-like conditions because soil moisture is not replenished.

  • Groundwater Contamination: Pollutants infiltrate aquifers → degrades potable water supplies.

  • Salt-Water Intrusion: When too much freshwater is pumped from coastal aquifers, the hydraulic pressure balance flips:

    • Saline water from the ocean migrates landward and upward, permanently replacing the freshwater in the system. Once replaced, the damage is essentially irreversible without expensive remediation.

• System-Level Takeaway

  • Over-extraction is not a simple local mistake; it re-writes the entire hydraulic gradient of a region.

  • Ethical implication: communities downstream or down-gradient inherit the costs (loss of drinking water, farmland collapse) without reaping the extraction benefits.

Nitrogen Pollution and Its Biological Consequences

• Uneven Nitrogen Management

  • Some landscapes or farms remain deficient (“clean”), while others receive heavy fertilizer inputs (“over-supplement”).

  • Leads to spatially skewed nutrient cycles.

• Nitrite vs. Nitrate Dynamics

  • Intended pathway: $\text{NH}<em>3 \rightarrow \text{NO}</em>2^- \rightarrow \text{NO}_3^-$ (ammonia → nitrite → nitrate).

  • Excess nitrogen, coupled with sub-optimal microbial conditions, stalls the pathway at the nitrite stage rather than completing into nitrate.

• Health Concern

  • Elevated nitrite ($\text{NO}_2^-$) levels are problematic:

  • They can convert hemoglobin to methemoglobin, reducing oxygen transport.

  • They form nitrosamines, compounds linked to carcinogenesis in human and animal cells.

  • Relationship to public health: infants (“blue baby syndrome”), cancer clusters near runoff areas.

• Broader Significance

  • Illustrates how incomplete nutrient processing has direct medical implications.

  • Connects agriculture, ecology, and healthcare policy.

• Integrated Perspective: Disrupted water systems and nitrogen mismanagement are not isolated issues; both exemplify how anthropogenic imbalances in natural cycles (hydrologic and biogeochemical) cascade into environmental degradation and human health risks. Remediation requires holistic strategies: sustainable withdrawal limits, balanced fertilizer application, and restoration of natural microbial pathways.

• Carbon cycle: transfer from “unavailable organic” fossil pool to “available inorganic” $\text{CO}_2$ pool.

• Fire suppression, soil erosion & nutrient depletion hamper natural renewal loops.

Planetary Contamination & Pollution

• Synthetic molecules alien to Earth biochemistry now detectable everywhere (air, water, soil, polar ice, deep ocean).

• Ecotoxicology + infectious agents + eutrophication + physical alteration of habitats.

Quantifying the Biodiversity Crisis

• Current extinction rate $= 10^2 \text{ to } 10^3$ times pre-industrial background.

• Freshwater species: extinction $\times 5$ higher than terrestrial.

• Examples- $13\%$ of all bird species threatened.

  • US: >$200$ plant spp. lost, $730$ federally listed as endangered.

  • Songbird density in US ↓ $50\%$ in $40$ yrs ("shifting baselines").

  • Lake Victoria: $\sim 300$ endemic cichlids → $\approx 100$ after Nile perch introduction.

Local California Snapshots

• >$90\%$ of S.F. Bay salt-marshes destroyed; endemic salt-marsh harvest mouse imperilled.

• Burrowing owl colonies disappearing with urban sprawl.

• Invasives: yellow star-thistle, French broom, eucalyptus, mitten crab, zebra mussel, kudzu, feral pigs.

• Pollution case studies- California condor: lead shot & antifreeze (ethylene glycol) poisoning.

  • Atrazine herbicide → male frogs feminised (endocrine disruption).

Climate Change & Greenhouse Physics

Greenhouse Principle

• Glasshouse analogy: atmosphere transparent to visible light, greenhouse gases (GHG) absorb outgoing IR heat.

• Essential baseline warming; excess GHG ⇒ excess warming.

$\text{CO}_2$ Trajectory

• Ice-core record $\rightarrow$ pre-industrial $\approx 280\,\text{ppm}$ .

• Post-Industrial Revolution exponential rise: >$415\,\text{ppm}$ today.

• Highest in >$2\times 10^5$ yr of hominin history.

Other GHGs (concentrations far lower)

• $\text{CH}_4$ (~$1.8\,\text{ppm}$)

• $\text{N}_2\text{O}$ (~$330\,\text{ppb}$)

• CFCs (parts-per-trillion; potent but now banned)

Anthropogenic Sources (US fraction)

• $87\%$ of man-made $\text{CO}_2$ from fossil fuels.- Electricity $\approx 38\%$

  • Transportation $\approx 22\%$

  • Industry $\approx 20\%$

Model vs Observation

• Natural forcings alone predict cooling; add GHG gives observed warming.

• Oceans absorbing heat: 0$–$200\,\text{m} layer shows strongest anomaly.

Consequences

• Sea-level rise to date $\approx 8''$ ($\approx20\,\text{cm}$); by 2100 projected +30$–120\,\text{cm} .- $\sim 52\%$ from land-ice melt, $\sim 38\%$ from thermal expansion.

• Coastal megacities & deltaic agriculture at risk (US East & Gulf Coast, CA Central Valley).

• Shifting biomes: Eastern temperate forests migrate N. to Canada; US breadbasket → boreal Canada.

• Estimated: $47\%$ of threatened mammals & $23\%$ of birds may lack climate resilience.

Stratospheric Ozone Depletion

• Ozone (O$_3$) layer (~20 km) absorbs UV-B.

• CFC photolysis releases $\text{Cl}^-$ radicals: $\text{Cl}+\text{O}<em>3\rightarrow\text{ClO}+\text{O}</em>2$ (catalytic).

• Polar vortex concentrates CFCs → "holes" over poles.

• Health/ecology: higher UV → skin cancer, cataracts, phytoplankton DNA damage.

• Montreal Protocol (1987) phased out CFCs; layer stabilising but full recovery decades away.

Conservation & Management Approaches

Precautionary Principle

• "Above all, do no harm" — act before full proof because remediation > prevention.

Habitat Strategies

• Bigger > smaller reserves; compact shapes minimise edge effects.

• Corridors connect sources (net exporters) to sinks (net importers) → maintain gene flow.- Example: wildlife overpasses across $\text{US 101}$ .

• Fragmentation maths: identical area in many pieces ↑ edge/area ratio, ↓ viable interior.

Reintroduction & Captive Breeding

• Successes: Tule elk, Californian condor, Père-David’s deer, Przewalski’s horse, Arabian oryx.

• Genetic rescue: prairie-chicken males translocated → hatching success ↑ from <20\% to >90\% .

Foundation & Keystone Species

• Beaver dams create wetland mosaics.

• Juncus in salt-marsh aerates soil, halves salinity & doubles species richness.

Umbrella Species & Policy Tools

• Charismatic fauna (e.g., spotted owl, grizzly, panda) galvanise habitat protection for co-occurring biota.

• US Endangered Species Act (1973): legal framework—listing ⇒ mandatory habitat safeguards.

• Controversial example: regulated trophy hunting in Africa funds large-scale private reserves (wildlife > cattle value).

Bioremediation & Augmentation

• Metal-accumulating fungi/lichens extract Pb, Hg, Cd.

• Hydrocarbon-digesting bacteria seeded & fertilised in oil-spill zones.

• Example: eutrophic Finnish lake restoration needed dual intervention.- Stage 1: stop sewage → no change.

  • Stage 2: heavy fishing ↓ planktivorous fish → zooplankton rebound → algal blooms collapse.

Ethical, Philosophical, Practical Threads

• "Shifting baselines" dull public sense of loss; education key.

• Cultural practices (e.g., bear-gall trade, shark-fin soup) collide with conservation ethics.

• Sustainable development demands radical redesign of energy, agriculture, economic incentives.

• Option A: act on science, innovate, and mitigate.

• Option B: status-quo → cascading ecological & socio-economic failures.