Environment & Sustainability: Climate Change, Water, and Biodiversity

Climate change — the mechanism

The greenhouse effect is the natural process by which certain atmospheric gases (water vapor, CO₂, methane, N₂O) absorb outgoing longwave radiation from Earth's surface and re-emit it — keeping the surface warmer than it would be without an atmosphere. Without the natural greenhouse effect, Earth's average surface temperature would be well below freezing.

Human activities — burning fossil fuels, land-use change (especially deforestation), and some agricultural practices — have increased atmospheric greenhouse-gas concentrations. This enhances the natural effect, warming the planet at rates and to levels unusual in the recent geologic record. Consequences include:

• Rising global average temperatures
• Sea-level rise from thermal expansion + melting land ice
• Shifting precipitation patterns (some regions wetter, others drier)
• More intense heat waves and heavier extreme precipitation events
• Ocean acidification (as oceans absorb ~1/3 of emitted CO₂)
• Ecological shifts — species ranges moving poleward and upslope

Mitigation vs adaptation

Two categories of response:

• Mitigation — reducing emissions or increasing carbon uptake (renewable energy, EVs, reforestation, carbon capture)
• Adaptation — reducing vulnerability to changes already underway (seawalls, drought-resistant crops, air conditioning, revised zoning)

Most countries pursue both, in varying mixes based on capacity and vulnerability.

The Paris Agreement (2015)

Nearly all UN member states adopted the Paris Agreement, committing to limit global warming "well below 2 °C" above pre-industrial levels, ideally 1.5 °C. Countries submit voluntary Nationally Determined Contributions (NDCs) — pledges of emission reductions, updated every 5 years. Not a treaty in the strict sense, but the most-signed climate agreement in history.

The Montreal Protocol (1987) — the success story

Addressed depletion of the stratospheric ozone layer caused by CFCs and related chemicals. Phased out production and use worldwide. The ozone layer has since been recovering. It is widely cited as the most successful international environmental agreement — a template for other issues (though climate has proven more difficult).

Water stress and scarcity

Water stress = demand approaches or exceeds sustainable freshwater withdrawal. Highest-stress regions: Middle East and North Africa, parts of South Asia, US Southwest, Northern China, and Australia's Murray-Darling basin.

Aquifer depletion is a specific concern where groundwater is being extracted faster than it recharges (Ogallala in US Great Plains, North China Plain, northwestern India).

Transboundary river disputes intensify with water stress — Nile (GERD dam), Tigris-Euphrates (Turkish upstream vs Syria/Iraq downstream), Mekong (Chinese and Lao dams), Central Asian Amu Darya and Syr Darya (Aral Sea catastrophe).

Deforestation

Main drivers vary by region:

• Amazon — cattle ranching (largest), soybean expansion, roads, colonization
• Congo Basin — subsistence agriculture + charcoal + selective logging
• Southeast Asia — oil palm expansion (Indonesia, Malaysia)

Consequences: biodiversity loss, carbon release, soil erosion, altered water cycles. Remote-sensing systems (INPE/PRODES in Brazil) monitor deforestation rates.

Desertification

Progressive degradation of dryland ecosystems from combined climate variability and human land pressures (overgrazing, unsustainable cropping, deforestation of woodland margins). Reduces vegetation cover and biological productivity. Sahel, Central Asia, northern China are canonical case regions.

Biodiversity hotspots

Regions containing very high concentrations of species (especially endemic) AND under significant threat from habitat loss. Recognized hotspots include Mediterranean Basin, Tropical Andes, Sundaland (Southeast Asian islands), Madagascar, California Floristic Province. The concept helps prioritize conservation attention geographically.

Coral bleaching

Elevated sea-surface temperatures stress coral, causing them to expel the symbiotic algae that provide most of their color and energy. Prolonged bleaching kills the coral. Great Barrier Reef, Caribbean, and other coral regions have experienced multiple large-scale bleaching events in recent years.

Marine plastic and gyres

Ocean gyres — large systems of circulating currents in each ocean basin — accumulate floating debris in their central regions. The "Great Pacific Garbage Patch" in the North Pacific Subtropical Gyre is the most-cited example. Microplastic (<5 mm fragments) is now present throughout ocean surface waters, seabeds, and marine food chains.

The energy transition

21st-century transition scales up solar, wind, hydropower, nuclear, and battery storage, displacing fossil fuels. Geographic implications: lithium and cobalt mining regions (Chile/Argentina/Bolivia lithium triangle, DRC cobalt), battery manufacturing hubs (China, South Korea, Japan, growing EU/US), grid infrastructure, and legacy petroleum-producer economies facing long-run revenue erosion.

Sustainable Development Goals (SDGs, 2015-2030)

The UN's 17 SDGs cover poverty, hunger, health, education, gender equality, water, energy, work, industry, inequality, cities, consumption, climate, oceans, biodiversity, peace, and partnerships. They set the current global development-and-sustainability policy framework. Successor to the 2000-2015 Millennium Development Goals (MDGs).