Earth's Interconnected Systems: Resources, Climate, and Impact

Earth Science Final Exam Review

April 14, 2025 – Lecture 18: Natural Resources – Energy and Mineral Resources

Natural Resources: An Introduction

Natural resources are materials or substances that occur in nature and can be used for economic gain. Humanity cannot create natural resources; they take millions, even billions, of years to form within Earth. Therefore, we are limited to what nature provides. Natural resources are broadly classified into eight groups: wildlife, air, wind, soil, water, fossil fuels, sunlight, and minerals (including precious metals like copper, gold, silver, nickel). Mineral resources, by definition, are inorganic, meaning they are not derived from living things (for example, coal is considered organic because it formed from ancient plant matter, so it isn’t classified as a mineral). Resources are widely distributed, but often in forms too dispersed to be immediately useful. Geologic processes concentrate materials into economically valuable deposits. A resource rarely “runs out” on Earth; instead, it becomes “too expensive to produce” once easily accessible deposits are depleted. As a resource becomes scarce, extraction costs rise, and we turn to alternatives. Mineral and energy resources are fundamentally important to modern standards of living; economies depend on them, and a growing population increases demand.

Energy vs. Mineral Resources

Earth’s natural resources can be grouped by origin: some are energy resources (like oil, gas, coal), some are mineral resources (metals, non-metallic minerals), others are biological resources (forests, fisheries), and so on. An “economic reserve” refers to the portion of a resource that is known and feasible to extract with current technology. This lecture focused on energy and mineral resources, with an emphasis on fossil fuels as energy sources.

Fossil Fuels: Usage and Trends

Fossil fuels (coal, oil, and natural gas) are energy-rich substances formed from the buried remains of ancient organisms. The mix of energy sources used by humans has changed over time, but total energy use has continually increased with civilization’s growth. Fossil fuel usage, in particular, expanded dramatically in the 20th century, becoming the dominant energy source of our industrial world. Even today, fossil fuels supply the majority of the world’s energy (around 80% as of 2022). This has huge implications for resource management and the environment. The concept of energy density was introduced: this is the amount of energy stored per unit mass of a fuel. Fossil fuels have relatively high energy densities, but nuclear fuel (like Uranium-235) contains far more energy per kilogram than any common fossil fuel. High energy density is one reason nuclear power is significant (though its use involves other considerations like safety and waste).

Oil and Natural Gas (Hydrocarbons)

Oil and gas are part of a class of chemicals called hydrocarbons – molecules made of hydrogen and carbon arranged in chains or rings. These hydrocarbons originate from the remains of plankton and other organisms that settled in mud on ancient sea or lake bottoms. Oil and gas form in a stepwise process:

• Organic matter accumulation: Dead microscopic organisms (like algae) and plant debris accumulate on the seafloor or lakebed, mixing with clay and mud. If the water is low in oxygen, this organic matter doesn’t fully decay.
• Kerogen formation: As layers of sediment bury this organic-rich mud, increasing heat and pressure slowly transform the organic material into a waxy substance called kerogen within a rock called organic shale. Kerogen is essentially fossil organic matter – a precursor to oil.
• Oil and gas generation: With deeper burial and temperatures above roughly 90°C, kerogen molecules break down into liquid and gaseous hydrocarbons – oil and natural gas. This typically happens between ~2–4 km depth in what geologists call the “oil window” of temperature. Oil is mostly generated at 90–160°C, and natural gas can form at slightly higher temperatures.
• Migration and trapping: Oil and gas, once formed in the source rock (the organic shale), are buoyant and tend to migrate upward through porous rock layers (they are less dense than water). They can move through permeable rocks until they get trapped by an impermeable barrier. A rock with sufficient pore spaces to hold oil/gas and with connections between pores to let fluids flow is called a reservoir rock (for example, a porous sandstone can serve as a good reservoir). A layer of rock that is impermeable (no connected pores) can act as a seal or cap rock, forming a trap that prevents the hydrocarbons from rising further. Common traps include folded layers (anticlines), faults, or salt domes that create a blocked pocket where oil and gas accumulate beneath the seal. When a significant quantity of oil or gas becomes concentrated and trapped in one place, we have a hydrocarbon reserve that can be drilled and extracted.

The lecture stressed the properties of porosity (the percentage of void space in the rock) and permeability (how well those voids connect) in creating a good oil/gas reservoir. High porosity means the rock can hold a lot of fluid; high permeability means fluids can flow through it easily. Sandstone, for example, often has both and is a typical reservoir rock. An impermeable shale or clay could serve as a seal above the reservoir.

Extracting Oil and Gas

Once a trap containing oil/gas is located, wells are drilled to extract it. Originally, wells were drilled vertically straight down into the reservoir (vertical drilling). Modern technology allows directional or horizontal drilling, where the well can be steered to travel laterally through the rock layer, increasing contact with the oil-bearing layer. Horizontal drilling is especially useful in shale or other reservoirs that are spread out horizontally but thin vertically. After drilling, if natural underground pressure is not enough to push the oil out, pumps are installed to pull it to the surface. In offshore reservoirs, large drilling platforms are used to drill through ocean water and into the seabed. Extracted crude oil is then transported (pipeline networks, tanker ships, etc.) to refineries, where it’s processed into fuels like gasoline, diesel, etc.

A significant technique in modern oil extraction is hydraulic fracturing (hydrofracking). In hydrofracking, a fluid (mostly water, mixed with sand and some chemicals) is pumped at high pressure into the rock formation to crack it open further. This creates new fractures and pathways, especially in rocks that had low natural permeability (like dense shale). The sand carried in the fluid stays behind in the cracks to prop them open, so that oil or gas can flow out more freely. Hydrofracking has unlocked large amounts of oil and especially natural gas from “tight” reservoirs (like shale gas in formations such as the Marcellus Shale). However, the method has environmental considerations (water usage, potential for groundwater contamination, induced seismicity, etc.).

Unconventional Reserves

The class distinguished conventional vs. unconventional hydrocarbon reserves. Conventional oil/gas reserves are those where the hydrocarbons are in a porous reservoir rock and readily flow into a well (making them relatively easy to extract by traditional drilling). Unconventional reserves are those where oil or gas cannot be simply pumped out using a standard well because the hydrocarbons are trapped in less permeable rocks or other forms. Examples of unconventional resources include: oil shale (rock that contains kerogen which hasn’t fully turned into oil; oil can be produced by heating the rock), tight oil/gas (oil or gas locked in low-permeability reservoirs like shale, requiring fracking to extract), and tar sands (also known as oil sands, where heavy oil called bitumen is mixed with sand and must be mined or steamed out). These resources often require specialized extraction techniques (mining, heating, fracturing) to produce oil or gas. Unconventional resources have become increasingly important in recent decades; for instance, shale fracking has made the U.S. one of the top oil and gas producers in the world in the 2010s.

Coal: Formation and Types

Coal is a fossil fuel, often described as “energy from the swamps of the past.” Coal forms from ancient plant material – mainly woody vegetation (trees, ferns, etc.) that died and accumulated in swampy, waterlogged environments. In such settings, the fallen plant matter is submerged in stagnant water where oxygen is low. Because there isn’t much oxygen, the usual decay and rotting of the wood is slow and incomplete. Instead of fully decomposing, the plant debris is gradually compacted and chemically altered. Initially it becomes peat – a brown, soft, spongy mass of compressed plant remains. As peat gets buried by more sediments over geologic time, heat and pressure drive out water and volatile compounds, transforming it into coal. The coal formation process is essentially a concentration of carbon: the deeper and hotter the burial, the more carbon-rich (and energy-rich) the coal becomes.

Coal is classified by rank, which reflects its degree of metamorphism (how much it has been altered by burial heat and pressure) and its carbon content:

• Peat: Not yet true coal, peat is the precursor – it forms at the surface in bogs/swamps. It has relatively low carbon content and still shows plant fibers. Peat can be dried and burned as a fuel, but it’s not very energy-dense.
• Lignite: Often called “brown coal,” this is the lowest grade of true coal. It forms from compressed peat. Lignite is soft, brownish, with ~25-35% carbon. It has relatively low energy content and is often used near where it’s mined.
• Bituminous coal: A mid-rank coal (sometimes just called “soft coal”), bituminous is formed under higher pressures and temperatures than lignite. It is darker, harder, and contains a higher percentage of carbon (around 60-80% carbon). Bituminous coal is widely used for electricity generation and in industry because it burns with a higher heat output than lignite.
• Anthracite: The highest rank of coal, anthracite (sometimes called “hard coal”) forms under the highest temperatures and pressures, approaching metamorphic conditions. It is glossy black, very hard, and has the highest carbon content (over 90% carbon) and energy density of any coal. Anthracite burns the cleanest (least smoke) and hottest, but is less common in nature than bituminous.

The progression is essentially peat → lignite → bituminous → anthracite as burial depth and heat increase. Each step drives off more water and volatile substances, concentrating the carbon. Thus, energy content per kilogram increases with rank.

Coal Resources and Distribution

Coal was formed in many parts of the world during past geologic periods (notably the Carboniferous Period ~300 million years ago, when lush swamp forests were widespread). As a result, large coal deposits exist on every continent. Worldwide coal deposits tend to accumulate in mid-continent basins, such as the Illinois Basin in the U.S. or the Kuznetsk Basin in Russia. In the United States, major coal regions include the Appalachian coal fields (bituminous coal), the Illinois Basin, and Powder River Basin (which produces a lot of sub-bituminous coal). Globally, countries like the United States, Russia, China, India, and Australia have some of the largest proven coal reserves. Coal remains an abundant resource (on the order of hundreds of billions of tons globally), but its usage is in decline in some regions due to a shift toward cleaner energy and climate change concerns.

Real-World Context of Energy Resources

While it’s unlikely we will literally run out of fossil fuels imminently, the easiest-to-obtain oil (from big conventional fields) has been largely tapped. Industry has moved increasingly to unconventional sources (fracking tight formations, mining tar sands, deep-water drilling) to meet continuing demand. This means the economics of extraction are critical; oil prices drive which resources are viable to exploit. Technology (like fracking or oil sands processing) has extended the life of the fossil fuel era, but also at environmental cost (greenhouse gas emissions, habitat disruption, etc.). It’s a balance between resource availability and the consequences of using those resources.

The reliance on fossil fuels also links to climate change. Fossil fuels still dominate the energy supply – roughly 80% of global energy consumption in recent years comes from coal, oil, and gas – meaning that transitioning to sustainable alternatives is a major challenge. This heavy use of fossil fuels is the primary source of carbon dioxide emissions driving global warming. This lecture set the stage by describing key Earth resources, how they form, and the limits and issues around their use, providing a foundation for understanding human impacts on Earth’s systems.

April 16, 2025 – Lecture 19: Freshwater Systems: Streams, Lakes, and Groundwater

Importance of Water and the Hydrologic Cycle

Water is absolutely essential for life, economies, and ecosystems. About 70% of Earth’s surface is covered by water (mostly oceans), yet freshwater is limited. Only about 2.5% of Earth’s water is freshwater, and most of that is locked up in glaciers/ice or hidden as groundwater; only a tiny fraction (less than 1%) is readily available in lakes, rivers, and the atmosphere for human use. Water is needed for domestic use, agriculture, industry, and energy production. Water also plays a critical role in regulating climate and weather patterns.

The hydrologic cycle (water cycle) is the continuous movement of water through Earth’s reservoirs: ocean, atmosphere, land, and living things. Key processes include evaporation, transpiration from plants, condensation forming clouds, precipitation (rain, snow), and runoff flowing back to oceans. Water also infiltrates into the ground to become groundwater, and can later return to the surface via springs or be taken up by plants. The cycle is powered by the sun (driving evaporation) and gravity (pulling water downhill). Monitoring components of the hydrologic cycle – precipitation, stream flows, groundwater levels, etc. – is important to manage water resources and predict hazards.

Problems in the Water Cycle

Disruptions or extremes in the water cycle lead to problems. Flooding is a natural part of the cycle (excess runoff when rainfall is too intense or snowmelt is rapid), but floods can devastate communities. Droughts are the opposite extreme – extended periods of low precipitation – which can dry up water supplies and ruin crops. Both floods and droughts are examples of hydrologic hazards that seem to be increasing or becoming more intense in many regions. Factors like climate change causing heavier downpours and land-use changes (urbanization creating fast runoff) contribute to increasing flash flood frequency. A warmer atmosphere holds more moisture, contributing to more extreme rainfall events in some areas, while shifting climate patterns can also exacerbate droughts elsewhere. Other issues include water contamination (floods can spread pollution or cause sewage overflows) and epidemics (stagnant floodwaters breeding disease, or drought forcing use of unsafe water).

Surface Water: Streams, Lakes, and Wetlands

Freshwater contains very low concentrations of dissolved salts (less than 500 parts per million salts). It exists as surface water (rivers, lakes, wetlands) and groundwater. Although freshwater is a small fraction of Earth’s total water, it is critical for drinking water, agriculture, and habitats. Most freshwater is either frozen in glaciers/ice caps or stored as groundwater beneath the surface, with only a small part on the surface as liquid.

Erosion and Deposition by Water

Water is a powerful geologic agent shaping Earth’s landscapes. Erosion is the process of water (or wind, ice) picking up and carrying away soil and rock, and deposition is when water drops the material it was transporting. Even in many desert environments, water causes more erosion than wind because when rare heavy rains do occur, the lack of vegetation means flash floods can quickly scour and move large amounts of sediment. Generally, flowing water in rivers erodes the land (especially when moving fast or in floods), and then deposits sediment when it slows down (for example, along a river’s inside bends or on floodplains). Water can slowly erode a canyon over millennia or rapidly strip away soil in a single storm. Deposition occurs when the water’s energy decreases – e.g., when a river overflows onto a flat plain, it deposits sand and mud, or when it reaches the ocean, forming a delta.

Stream Formation and Behavior

A stream (a term that includes rivers, creeks, etc.) forms from water flowing downslope under gravity. When rain falls or snow melts, some water runs off over the land surface (as opposed to infiltrating). Initially, water may flow as a thin sheet (sheetwash) across the ground. As it finds low spots, it begins to concentrate into small channels. Over time, flowing water downcuts into the substrate, carving a deeper channel by erosion. This process, combined with tributaries joining, leads to an organized drainage network of streams. Streams carve valleys and can create features like meanders – looping curves that migrate over time. A classic feature of meandering rivers is the formation of oxbow lakes. As a river’s meanders become extreme, sometimes during a flood the river will cut a new, shorter channel and cut off the meander loop, leaving behind a curved lake where the river used to flow.

River Flooding and Flood Control

Rivers naturally experience periods of high discharge (volume of water flow) that can overflow banks – floods. Two types of floods are slow-onset floods, which develop over days or weeks (often from prolonged rain or snowmelt upstream), and flash floods, which come on very quickly (within hours or even minutes) and can be very dangerous. A flash flood typically occurs due to intense rainfall over a small area (or dam/levee breaks) and can catch people off guard because of its suddenness. It may be impossible to escape the path of a flash flood in some cases. Flash flood frequency is increasing due to climate change (heavier short-duration rain events) and urbanization (paved surfaces cause rapid runoff).

To mitigate flood risks, humans have employed various flood control measures. Examples include artificial levees and floodwalls, which are embankments or walls built along rivers to keep water contained. Wetland restoration is also mentioned – wetlands act as natural sponges and storage areas for floodwater, so preserving or restoring them can help blunt the impact of floods. However, all these measures have limits; if a levee is overtopped or breached, the sudden release of pent-up water can be catastrophic.

Groundwater and Aquifers

A significant portion of this lecture dealt with groundwater – water that resides under Earth’s surface in pore spaces of soil and rock. Key terms:

• Aquifer: a geological formation (rock or unconsolidated sediment) that can store and transmit water readily – in other words, a water-bearing layer with high porosity and permeability. Good aquifers are often composed of sand, gravel, or fractured rock where water can flow.
  • Unconfined aquifer: one that is open to receive water from the surface, usually with the upper surface of the groundwater (the water table) forming its top.
  • Confined aquifer: one that is bounded above (and often below) by impermeable layers (aquitards). Confined aquifers are pressurized; water in a well tapping a confined aquifer can rise above the aquifer level (artesian well) due to that pressure.
• Aquitard: a layer of rock or sediment with low permeability that slows or prevents water movement (also called a confining layer). Clay or unfractured shale are good examples of aquitards. They may hold water, but it doesn’t transmit well.
• Water Table: the boundary in the ground between the unsaturated zone above (pores contain air and water) and the saturated zone below (pores fully filled with water). The water table depth fluctuates with rainfall and pumping – it rises with recharge (addition of water) and falls with extraction or drought. Below the water table, groundwater flows (slowly) from high-pressure areas to low-pressure areas, often eventually discharging into streams, lakes, or the ocean.

Groundwater is a crucial freshwater reservoir; in many regions, more water is stored in aquifers than in surface bodies. It supplies drinking water via wells and is used heavily for irrigation. However, groundwater is being depleted in many areas due to overuse (pumping out faster than natural recharge can replenish). Groundwater is depleting everywhere, raising the issue of groundwater recharge problems, especially due to pollution (if recharge water is contaminated, it pollutes the aquifer).

Groundwater also plays a role in forming geological features like caves. Most caves form in limestone rock by a process of chemical erosion: as slightly acidic groundwater percolates through limestone bedrock, it dissolves the rock, carving out cavities. Caves typically form just below the water table. When the water table later drops, these cavities drain and become air-filled caves. Water dripping in caves can precipitate calcite to create stalactites, stalagmites, and other cave deposits (speleothems). If a cave grows large and its roof becomes too thin, it can collapse, causing a sinkhole at the surface. A dramatic example shown was a sinkhole in Florida, where such collapses are relatively common due to abundant limestone and pumping of groundwater.

Threats to Freshwater Supplies

Human activities threaten both water quality and quantity. Key threats include:

• Pollution: Introduction of harmful substances into water. This can be industrial chemicals, agricultural fertilizers/pesticides, sewage, or other pollutants. Pollution can make water unsafe to drink and harm aquatic life.
• Eutrophication: An oversupply of nutrients (especially nitrogen and phosphorus, often from fertilizer runoff or sewage) in a water body causes excessive algae growth. When the abundant algae die and decompose, the process consumes oxygen, leading to oxygen depletion in the water (hypoxia). This can kill fish and create “dead zones.” This is a common problem in lakes and coastal waters (e.g., the Gulf of Mexico dead zone from Mississippi River runoff). This is also called cultural eutrophication.
• Dam construction: Dams alter the natural flow of rivers, which can trap sediments and affect ecosystems downstream. Dams provide benefits (water storage, electricity, flood control) but they change sediment transport and can starve downstream deltas of sediment, impacting fish migration.
• Water depletion: Excessive withdrawal of water for human use can deplete rivers, lakes, and groundwater. Examples include lakes drying up from diversion (the Aral Sea) and groundwater aquifers dropping (e.g., the Ogallala Aquifer). If more water is taken out than nature puts back (recharge), the resource is effectively mined and can run out locally.
• Changes in infiltration and runoff: Urbanization (paved roads, buildings) prevents water from soaking into soil, increasing surface runoff and reducing groundwater recharge. The loss of vegetation (from deforestation or overgrazing) also means more runoff and erosion, because plant cover normally helps water soak in and holds soil in place. Human land use can exacerbate flooding, erosion, and reduce the natural resupply of groundwater.

A vivid real-world example is the recurring toxic algal blooms in lakes (like the algae bloom that shut down Toledo, Ohio’s water supply in 2014 due to fertilizer runoff in Lake Erie) or the dead zones in coastal oceans each summer.

In summary, this lecture covered how water moves through the environment (the hydrologic cycle), how water shapes landscapes, and how crucial freshwater is – along with the hazards and challenges of too much water (floods), too little water (droughts), and degraded water (pollution). Understanding these concepts is key for managing water resources sustainably, a theme that connects to later discussions on climate change and human impacts on Earth systems.

April 21, 2025 – Lecture 20: Drought, Groundwater, and Desert Landscapes

Continuing Groundwater (Local Context)

This lecture began by wrapping up water resources and moving into the topic of desert landscapes. A local perspective on water issues was provided, especially focusing on drought and water supply in California. Southern California’s water supply is a complex system, as the region has a dry climate and relies on water imported from elsewhere (like Northern California and the Colorado River) as well as local groundwater. The Orange County Groundwater Replenishment System (GWRS) was referenced – a project that takes treated wastewater and further purifies it to recharge the aquifer (effectively recycling water). This is an innovative water management method to conserve water in a semi-arid region facing recurrent drought.

Drought and Its Consequences

Drought – an extended period of deficient rainfall – is a recurring challenge in California and many parts of the world. Repercussions of drought include:

• Economic impacts: Water shortages can reduce hydroelectric power generation. Farmers may have to fallow fields, driving up food prices. Industries can face higher costs if water is scarce, and prolonged drought can even cause job losses in agriculture and related sectors.
• Environmental impacts: Drought stresses ecosystems. Habitats like wetlands shrink; rivers run low or dry, affecting fish and wildlife. Lack of water and food can lead to wildlife population declines or force animals to migrate. Vegetation dies back, which can lead to soil erosion and dust storms when winds pick up.
• Social impacts: Droughts can trigger depression in farming communities due to economic hardship. Water shortages can cause public health issues if water quality degrades (e.g., concentration of pollutants in dwindling water supplies, or lack of clean water for sanitation). Drought also increases the risk of wildfires, which then degrade air quality. Competition for water between cities, farms, and the environment intensifies, sometimes leading to political conflict.

Globally, drought is one of the costliest natural disasters; for example, multi-year droughts in the Horn of Africa have led to food insecurity for millions. Climate change is expected to make dry areas drier in many cases and alter precipitation patterns.

California Drought Example

California’s recent drought history was examined, comparing a wet year (2019) with a very dry year (2022). California went from relief in 2019 (after a major drought from 2012-2016) to extreme dryness by 2022 (the 2020-2022 drought). Most water infrastructure was built pre-1970, highlighting that California’s water storage and conveyance system is aging and wasn’t designed for today’s climate challenges or population. Climate change is projected to decrease snowpack (critical for California’s water supply), prolong droughts, and also create flashier floods when rain does come. This presents 21st-century problems for water management, as the state’s historical system is being strained by more extreme swings.

Transition to Deserts

After covering drought, the lecture transitioned into desert landscapes. A desert is commonly thought of as a region that receives very little precipitation. A key point is that deserts are defined by aridity, not temperature. A desert is an area that is extremely dry – typically defined as receiving less than 25 cm (10 inches) of rain per year. It can be hot (like the Sahara) or cold (like the Gobi in winter or the polar deserts). Deserts cover about 25% of Earth’s land surface. Cold deserts have average temperatures below ~20°C, while hot deserts have summertime temperatures around 35°C or more. The presence of low precipitation is the defining factor.

Deserts are sources of dust that can be transported globally and have impacts on air quality and health. With climate change and human land misuse (overgrazing, deforestation), desertification (the expansion of desert-like conditions) is a concern, so monitoring changing desert areas is important.

Nature of Deserts

Summarizing the nature of deserts:

• Very low rainfall (<25 cm/year).
• Vegetation is sparse or adapted to drought (cacti, shrubs, etc.).
• High evaporation rates often mean even moisture that comes can evaporate quickly.
• Deserts can be hot or cold, but all share water scarcity.
• Often clear skies and intense sunshine, which causes big temperature swings between day and night because dry air doesn’t retain heat.

Identifying Desert Regions

Deserts can form under different climatic and geographic circumstances:

• Subtropical Deserts: These are the big hot deserts around 20°–30° latitude (north and south). They form under global circulation patterns where air that rose near the Equator descends around the subtropics. Descending air is dry and warms, causing high evaporation and clear skies. Examples include the Sahara, Arabian, Kalahari, and Australian Outback.
• Rain-Shadow Deserts: These occur on the downwind side of mountain ranges. Moist air rises over mountains, cools, and drops rain on the windward side, becoming dry by the time it passes over the crest. Examples: the Mojave Desert and Great Basin in the U.S. (in the rain shadow of the Sierra Nevada and Cascades); the Gobi Desert (in the rain shadow of the Himalayas).
• Coastal Deserts: Some deserts lie along coasts where cold ocean currents chill the air and inhibit evaporation, leading to very little precipitation inland. The cold currents often induce a temperature inversion that suppresses rainfall. Examples: the Atacama Desert in Chile (next to the cold Humboldt Current) and the Namib Desert in Namibia (next to the cold Benguela Current).
• Continental Interior Deserts: Places far from oceans can become very dry because most moisture rains out before reaching deep inland. Examples include the interior of Asia (e.g., parts of Kazakhstan, or the Gobi in Mongolia/China).
• Polar Deserts: Cold polar regions get very little precipitation (cold air holds little moisture). Antarctica and parts of the Arctic are technically deserts in terms of precipitation. They are frigid deserts of ice.

This lecture introduced desert definitions and types, setting up for deeper coverage of desert geology and the introduction of glacial landscapes in the next lecture. The key takeaway was understanding why certain areas become deserts and recognizing drought as both an episodic hazard and a window into desert climate conditions. California’s struggles with drought offered a contemporary example of water scarcity, which in extreme could lead to desert-like conditions if not managed.

April 23, 2025 – Lecture 21: Desert Processes and Glacial Landscapes

Causes of Deserts (Recap)

This lecture continued the desert topic, reiterating the various causes of deserts worldwide: subtropical highs, rain shadows, coastal cold currents, continental interiors, and polar cold. For each cause, an example was discussed (Sahara for subtropical, Mojave for rain shadow, Atacama for coastal, Gobi for interior, Antarctica for polar). Recognizing these helps predict where deserts occur on the globe.

Desert Weathering and Soil

In deserts, physical weathering often dominates over chemical weathering because of the scarcity of water. Desert weathering might include intense heating and cooling that cracks rocks (thermal stress), and occasional rainstorms that cause flash floods doing abrupt erosion. Desert soil tends to be thin, with little organic matter, often a coarse sand or dust.

Erosion by Water in Deserts

Even though deserts are dry most of the time, water is still a major force in shaping them. When rain does fall, it often comes as short, heavy bursts. With sparse vegetation to hold the soil, runoff is rapid and can carve the landscape quickly. Over geological time, infrequent but intense water flows create features like dry stream channels (arroyos), alluvial fans (cone-shaped deposits of sediment at the mouths of canyons), and playas (dry lake beds where water occasionally ponds and evaporates, leaving salt crusts).

Erosion by Wind

Wind is another significant agent in deserts due to the lack of plant cover and dry, loose sediments. Wind transports sediment as suspended load (fine particles like clay and silt lifted high in the air, staying aloft for long distances, forming dust storms) and surface load (sand grains and larger particles moving by saltation – a hopping, bouncing motion along the ground – or by rolling in strong winds). This surface creep forms sand dunes when sand accumulates in mounds.

Wind Erosional Features

Wind can abrade surfaces, sandblasting rocks and creating ventifacts (rocks polished or faceted by wind-driven sand). It can also selectively remove finer particles, leaving a surface of gravel behind called desert pavement. Over time, wind erosion can carve interesting rock shapes.

Desertification

A critical topic was desertification – the process by which semi-arid land is transformed into desert in a matter of decades. Causes include drought, overpopulation, overgrazing by livestock, intensive farming (which can deplete soil), diversion of water (rivers or groundwater pumping that dries out land), and climate change. An example given was the Sahel region on the southern edge of the Sahara in Africa, which has experienced desertification due to drought combined with overuse of land. Desertification is a global concern because it can render once-productive lands infertile and displace populations. Managing grazing, planting drought-resistant vegetation, and sustainable water use are key to preventing it.

Another striking example was the Aral Sea in Central Asia. Once one of the world’s largest lakes, it has shrunk dramatically since the 1960s due to diversion of rivers for irrigation. The exposed lakebed became a salty desert, and dust storms blow toxic, salty dust from it, affecting local climates and health. This is a human-caused “desert” where a water body used to be – a cautionary tale of unsustainable water management.

Glaciers: An Introduction

After covering deserts, the lecture shifted to the other end of the spectrum: glaciers. Glaciers are essentially “rivers of ice” – large masses of ice that flow under their own weight. The formation of glaciers was outlined as follows:

• Glaciers form in places where snow accumulates year after year without completely melting in summer. Over time, layers of snow compress into firn (granular snow) and then solid ice.
• Snow and ice build up to sufficient thickness (typically at least ~50 meters thick) and the pressure causes the base ice to become ductile. At that point, the mass of ice begins to flow outward or downhill under gravity. This flow is very slow.
• Glaciers can develop in polar regions (very high latitudes) and on mountains at any latitude, as long as it’s cold enough for snow to persist.

Two main types of glaciers are continental glaciers (ice sheets) like those covering Antarctica and Greenland, which are huge and cover entire landmasses, and alpine (mountain) glaciers which flow down valleys in mountainous areas (also called valley glaciers).

Glaciers store the largest source of freshwater on Earth. The majority of the world’s freshwater is locked up in glacial ice. If all this ice melted, sea levels would rise dramatically. Glaciers are also important because they are sensitive indicators of climate – when climate warms, glaciers retreat; when climate cools, they advance.

Modern Relevance: Glacial Retreat

Glaciers have significant impacts on landscapes through glacial erosion and deposition. Glacial erosion can carve out U-shaped valleys (unlike the V-shaped valleys of rivers) as glaciers grind down bedrock. They pluck and abrade rock, often leaving polished surfaces and grooves (striations). Glaciers can carry rocky debris of all sizes and deposit them as moraines (ridges of till at the glacier’s sides or end) when the ice melts.

Many mountain glaciers worldwide are currently retreating due to global warming, visibly altering landscapes and threatening water supplies for some communities. The importance of glaciers as freshwater sources also ties to concerns that their loss will impact irrigation and hydropower in places like the Andes or Himalayas. All these issues bridge into the next topics of climate change.

In conclusion, this lecture juxtaposed two very different environments – deserts, shaped by dryness and often by wind, and glacial landscapes, shaped by ice. Yet, both environments can tell us about climate (deserts expanding with warming/drying, glaciers retreating with warming). Both also pose challenges: desertification threatens livelihoods in arid regions, while glacial melting poses risks like sea-level rise. Understanding the natural processes in these systems gives insight into past climate changes and helps us anticipate future changes in a warming world.

April 30, 2025 – Lecture 23: Ocean Systems and Sea-Level Rise

Oceanic Life and Nutrients

This lecture shifted focus to the oceans – covering their physical structure, life, and pressing issues like sea-level rise. Oceans are teeming with life, especially in surface waters where sunlight allows photosynthesis. Tiny phytoplankton (microscopic algae) form the base of the marine food web. Phytoplankton use sunlight and nutrients (like nitrate, phosphate, iron) to grow, and in turn feed zooplankton and larger organisms. Nutrients in the ocean are not evenly distributed; they tend to be scarce at the surface and more abundant in deep water. Upwelling areas, where deep water rises, bring nutrients to the surface and create rich fisheries.

Dissolved Oxygen

The ocean also has varying levels of dissolved oxygen. Near the surface, water is oxygenated by exchange with the atmosphere and by photosynthesis. But at mid-depths, there are often oxygen minimum zones where respiration of organic matter by bacteria uses up oxygen and there’s little mixing to replenish it. These low-oxygen layers can be problematic for marine life. The deep ocean is oxygenated in places where cold surface water sinks, like around Antarctica and Greenland – a concept related to thermohaline circulation.

Global Ocean Circulation

The lecture likely touched on ocean circulation, as the mention of nutrients and chlorophyll distribution suggests understanding where high productivity is (like around Antarctica, in equatorial upwellings, etc.) which ties to currents. Chlorophyll distribution maps (satellite data) show ocean color as a proxy for phytoplankton concentration – typically high at high latitudes and in upwelling zones, low in the central ocean gyres (desert-like regions of the ocean).

Bathymetry: Mapping the Seafloor

The lecture then covered aspects of ocean geology. Bathymetry is the study of the depths and shapes of the seafloor (underwater topography). It involves mapping underwater features using reflected waves (like sonar). For example, the Turneffe Seamount was mentioned. Ships and satellites use sonar and altimetry to measure ocean depths, revealing mid-ocean ridges, trenches, seamounts, etc. Additionally, seismic reflection surveys involve sending sound waves that penetrate the seafloor and reflect from different sediment and rock layers, helping geologists infer the structure beneath the seafloor (useful for oil exploration, studying plate boundaries, etc.).

Deep-Sea Drilling

The lecture highlighted scientific ocean drilling, e.g., the JOIDES Resolution research vessel. This ship drills into the seafloor to retrieve core samples of sediment and rock. Scientific drilling has been crucial in discovering Earth’s climate history (through sediment layers), the age of the ocean crust, and the presence of resources. The JOIDES Resolution is part of the International Ocean Discovery Program (IODP). By drilling into the seafloor, scientists can directly study the composition and history of ocean basins.

Sea-Level Rise

A critical modern issue covered was global sea-level rise. The ongoing sea-level rise is estimated to be about 3.2 mm per year (a rate that has edged upwards recently to closer to ~3.7 mm/yr as of the 2020s). Sea-level rise occurs due to thermal expansion of ocean water as it warms and the melting of land ice (glaciers and ice sheets adding water to the oceans). Although a few millimeters per year sounds small, it adds up: ~3.2 mm/yr means ~32 cm (over a foot) per century, and it may accelerate. Low-lying coastal regions, small island nations, and coastal cities are at risk. The threat is not abstract: we are already seeing increased coastal erosion and more frequent high-tide flooding. Major cities worldwide will face greater flood risks. Sea-level rise is a significant consequence of global warming and a challenge for the coming decades.

Estuaries

An estuary is a coastal water body where freshwater from rivers mixes with seawater. Estuaries are river valleys flooded by sea-level rise. Many estuaries formed at the end of the last Ice Age, when sea level rose dramatically as ice sheets melted, and ocean water invaded river valleys. Example: Chesapeake Bay in the USA is a drowned river valley that filled with ocean water, creating a rich estuarine ecosystem. Estuaries are typically nutrient-rich and productive (they often support fisheries and abundant wildlife) because they receive sediments and nutrients from land but also have tidal flushing from the ocean. They are brackish (mixed salinity). With ongoing sea-level rise, estuaries may penetrate further inland, and new areas may become estuarine in character.

Coastal Wetlands

Coastal wetlands include salt marshes in temperate zones and mangrove swamps in the tropics – flat, vegetated coastal areas that are regularly flooded by tides but are sheltered from strong waves. Coastal wetlands are incredibly important: they serve as nurseries for fish, protect shorelines from erosion by damping waves, and store carbon. However, coastal wetlands are threatened by development and sea-level rise. If sea level rises faster than wetlands can build up sediment or migrate landward, they can be submerged and lost. The lecture likely touched on the importance of these wetlands and the need to preserve them as natural buffers.

Ocean and Climate: Phytoplankton and Carbon

The professor provided deeper insight into how oceans and climate are interconnected via the carbon cycle, focusing on phytoplankton. Marine phytoplankton play an outsized role in the global carbon cycle by absorbing CO₂ from the atmosphere during photosynthesis. When phytoplankton bloom, they draw down CO₂, some of which can eventually sink to the deep ocean as organic matter – this is sometimes called the biological pump. The carbon that sinks can be stored in deep waters or sediments for long periods, keeping it out of the atmosphere. This process helps regulate climate by sequestering carbon.

Satellites can monitor surface chlorophyll and thus estimate phytoplankton abundance from space. However, satellites only “see” the surface layer; what happens below is harder to track. Carbon storage isn’t uniform across the oceans: it’s highest in the North Atlantic and North Pacific and lowest in subtropical regions. Subtropical gyres are nutrient-poor and have less biological productivity, hence less carbon drawdown. As the climate warms, subtropical areas may expand, potentially reducing the ocean’s efficiency at storing carbon. Warming can increase stratification (layers in the ocean) that prevent nutrients from mixing up, thus starving surface plankton and weakening the biological pump.

The next lecture would delve into the atmosphere and climate explicitly, a logical flow after covering oceans.

In summary, this lecture underscored that the oceans are a dynamic system: they harbor life, influence climate, and are changing (sea levels rising, possibly less capable of absorbing carbon if stratification increases). The take-home lessons include understanding sea-level rise and its causes/effects, knowing what estuaries and wetlands are (and why they matter), and recognizing the oceans’ role in the carbon cycle and climate regulation.

May 5, 2025 – Lecture 24: Atmospheric Structure and Processes

Atmospheric Composition and Structure

This lecture moved into Earth’s atmosphere – its layers, composition, and phenomena like aerosols and weather elements. The atmosphere is roughly 78% nitrogen (N₂), 21% oxygen (O₂), and small amounts of argon, CO₂ (~0.04%), and other gases. The structure of the atmosphere is divided into layers defined by temperature gradients:

• Troposphere: the lowest layer, where we live and where weather happens. It extends ~8 km at the poles to ~15 km at the equator. Temperature decreases with elevation in the troposphere because the surface is heated by the sun and then warms the air above. The top of the troposphere (tropopause) is the coldest point.
• Stratosphere: above the tropopause (~15 to 50 km). In the stratosphere, temperature actually increases with height. This inversion is due to the ozone layer, which absorbs ultraviolet (UV) radiation from the sun and warms up. The presence of ozone (O₃) is critical as it filters out most of the sun’s harmful UV-B rays, protecting life on Earth. The inversion also makes the stratosphere very stable.
• Mesosphere: above ~50 km up to ~80–85 km. Here, temperature again decreases with height (the coldest atmospheric temperatures, around -90°C, occur near the top of the mesosphere). The mesosphere is where meteors burn up.
• Thermosphere: above ~85 km, going hundreds of km up (includes the ionosphere). In the thermosphere, temperature increases with height (very high temperatures, hundreds to thousands of degrees, but the air is extremely thin). This is where the auroras occur and also where the International Space Station orbits.
• Ionosphere: Not a distinct layer, but a region (mostly in the thermosphere) where solar radiation ionizes gases, creating charged particles. It’s important for radio communication and for auroras.

Each boundary (tropopause, stratopause, mesopause) is where the temperature trend flips.

Atmospheric Aerosols

The lecture introduced aerosols, which are tiny solid or liquid particles suspended in the air. Aerosols can come from natural sources or human activities. Examples given:

• Inorganic aerosols: e.g., mineral dust (like dust from deserts), sea salt (from sea spray), sulfates (from volcanic SO₂ or industrial emissions), volcanic ash, soot (black carbon from fires or combustion).
• Organic aerosols: e.g., pollen, bacteria, molds, viruses.

Aerosols affect air quality (harming health), visibility (haze), and even climate (aerosols can cool Earth by reflecting sunlight, or warm it if they’re soot that absorbs sunlight). Dust from the Sahara can blow across the Atlantic, fertilizing ocean and rainforest ecosystems, but also causing respiratory problems downwind. Smoke from forest fires is another major aerosol.

Photochemical Smog

The lecture discussed smog, specifically photochemical smog as seen in cities like Los Angeles. Photochemical smog is a brownish haze caused by the reaction of sunlight with pollutants like nitrogen oxides (NOx) and volatile organic compounds (VOCs) from car exhausts and industrial processes. These reactions produce ozone (O₃) at ground level (which is harmful to lungs and plants) and a mix of other irritating compounds. Smog includes a load of aerosols too, contributing to poor visibility.

Natural vs. Anthropogenic Pollution Sources

Natural sources of atmospheric pollution include:

• Breathing (exhaling CO₂).
• Dust storms (natural events that loft dust).
• Volcanic emissions (volcanoes release sulfur dioxide, ash, etc.).
• Biological decay (rotting matter releases methane, for instance).
• Wildfires (emit smoke, CO₂, CO, etc.).

Anthropogenic (human) sources include burning of fossil fuels (power plants, vehicles), industrial processes, agricultural activities, and waste burning. The distinction is that human activities have greatly increased the amount of pollutants and introduced some that are not significant naturally. Many air pollutants are also greenhouse gases or lead to their formation.

Key Atmospheric Properties

The lecture highlighted main properties we measure to describe weather and climate:

• Air temperature: measure of how hot or cold the air is.
• Atmospheric pressure: the weight of the air column above, which decreases with altitude. It influences weather.
• Relative Humidity (RH): the amount of water vapor in the air relative to the maximum it could hold at that temperature. Warm air can hold more moisture. At 100% RH, the air is saturated and condensation can occur (dew or rain). RH is highest in cool mornings and lowest in hot afternoons if moisture is constant.
• Wind speed and wind direction: wind is simply air moving horizontally. Direction is reported from where the wind blows (e.g., a north wind blows from north to south). Speed is measured with an anemometer.
• Visibility: how far one can see (affected by aerosols, fog, etc.).
• Cloud cover: amount of sky covered by clouds.
• Precipitation: any water falling from the sky (rain, snow, etc.), measured in amount.

These factors are the basis of a weather report and crucial for understanding climate (long-term averages of these).

Wind

Horizontal movement of air is wind, and winds are named for where they come from. Wind exists because of pressure differences: air moves from high-pressure areas to low-pressure areas, deflected by Earth’s rotation (Coriolis effect) and friction with terrain.

Weather vs. Climate

The lecture likely clarified the difference between weather (day-to-day state of the atmosphere) and climate (long-term average patterns of weather). This sets up the next lecture on climate change.

Air Pollution and Health

The lecture might have begun touching on air pollution problems, such as smog’s health impact (asthma, respiratory issues). Air pollution can cause lung disease, heart problems, etc., and improving air quality has been a major success in some places. The focus on aerosols and pollution indicates an integrated approach to atmosphere science, bridging into human impacts and climate.

To summarize this lecture: it provided a foundation in how the atmosphere is built (layered structure, composition), what particles/aerosols exist in it, and what variables characterize weather. This knowledge is crucial for understanding how phenomena like the greenhouse effect or ozone depletion work, and underpins understanding of climate change.

May 7, 2025 – Lecture 25: Climate Change and Global Environmental Issues

Atmospheric Pollution Recap

This lecture likely finished any remaining notes on air pollution. Specific human sources of pollution include crop residue burning, biomass burning, forest fires, and aviation. Their effects are poor visibility, dense haze/fog/smog, poor air quality, and threats to health. Burning crop residue and biomass produces a lot of smoke and particulates. Forest fires also emit smoke and greenhouse gases. Aviation contributes CO₂ and also contrails and NOx at high altitudes, which can affect climate and produce visible haze. These pollution sources result in smog and haze that reduce visibility and degrade air quality, as well as causing respiratory and cardiovascular health problems. Human actions are altering atmospheric composition both in terms of air quality and climate.

Climate Change Basics

The lecture then fully delved into climate change – primarily the current global warming trend.

A key figure introduced was the Keeling Curve. This is the famous record of atmospheric CO₂ concentration measured at Mauna Loa Observatory, Hawaii, started in 1958. It shows a steady upward climb of CO₂ from about 315 ppm (1958) to over 420 ppm today, with seasonal oscillations. The Keeling Curve is iconic evidence that CO₂ is rising due to human activities (burning fossil fuels, deforestation). Currently (2025) CO₂ is around 420 ppm – about 50% higher than pre-industrial levels.

The lecture defined terms:

• Climate change: a significant change in the set of weather conditions (temperature, precipitation, etc.) that becomes the new norm for a region or the planet. Essentially, a long-term shift in climate.
• Global warming: specifically refers to an increase in the average global temperature (both atmospheric and sea-surface). It’s a subset of climate change.
• Global cooling: a decrease in average global temperature.

These definitions make clear that climate change could be warming or cooling, but currently we are concerned with warming. The cause of current global warming is the enhanced greenhouse effect – excess greenhouse gases (CO₂, methane, etc.) from human activities trap more heat.

Long-Term Climate Change Controls

This portion addressed factors that can change Earth’s climate over geologic time. Long-Term Climate Change Controls included:

• Sea-level change: Higher sea levels and flooded continental areas can change heat distribution, altering climate.
• Volcanic activity: On very long timescales, more volcanism adds CO₂ to the atmosphere (a greenhouse gas), which can warm climate. Over short timescales, a single big volcanic eruption can actually cool climate by injecting aerosols (sulfur) that reflect sunlight.
• Uplift of land surfaces: When land is uplifted (mountain building) and fresh rock is exposed, chemical weathering increases. Weathering of silicate rocks consumes CO₂ from the air, causing cooling.

This holistic view shows that Earth’s climate has changed in the past due to natural factors. But those factors are too slow or not aligning with the rapid warming observed now, which points to human GHG emissions as the culprit for current climate change.

Volcanic Aerosols Example

The lecture gave the case of Mt. Pinatubo (Philippines, 1991) which erupted massively, injecting sulfur dioxide and ash into the stratosphere. This created a veil of sulfate aerosols globally, which reflected sunlight and caused a measurable cooling (~0.5°C globally) and altered precipitation patterns for a couple of years. This example shows how a large volcanic eruption is like a natural “geoengineering” that cools climate temporarily.

Evidence of Recent Climate Change

Multiple lines of evidence indicate that climate is currently warming:

• Observed temperature change: Thermometer records over the last century+ show ~1.1–1.2°C rise in global average temperature since the late 19th century. Each of the last few decades has been warmer than any decade before.
• Observed sea-level change: Tide gauges and satellite altimeters show that global sea level has risen ~20 cm since 1900, and the rate has accelerated in recent decades. This is due to melting ice and thermal expansion.
• Global glacial retreat: Mountain glaciers almost everywhere are retreating as the world warms. Photographic evidence, glacier mass balance measurements, and the shrinking of Arctic sea ice and ice sheets all confirm warming.
• Distribution of organisms: Many plant and animal species are shifting their ranges toward poles or to higher elevations as climate zones move. Coral reefs bleaching is another biological indicator.
• Changes in global weather patterns: Increased frequency of extreme weather events – more heat waves, heavier downpours, more intense hurricanes, etc., consistent with a warming climate.

All these evidence streams reinforce that warming is happening now and affecting natural systems. The scientific consensus attributes this warming to human causes.

Earth Systems Coupling

The climate system is an interplay of all Earth’s “spheres”: Land-Ocean-Atmosphere-Biosphere-Cryosphere. Changes in one component can feedback to others. For instance, a warming atmosphere melts ice, which changes ocean circulation and sea level and reduces habitat for polar species. The climate system is interconnected, so all parts must be considered together.

Impacts of Pollution/Aerosols

Adverse impacts of pollution or increasing atmospheric aerosols include:

• Health: Air pollution shortens lives (e.g., 7 million deaths a year due to air pollution, causing respiratory and heart diseases).
• Weather conditions: Pollution can influence rainfall patterns.
• Monsoon: Heavy aerosol pollution can weaken monsoon circulations.
• Snow/Glaciers: Deposition of black carbon on snow reduces its albedo and accelerates melting.
• Visibility: Haze and smog reduce how far we can see.
• Ocean ecology: Some aerosols deposit nutrients, but pollution also causes ocean acidification via CO₂.
• Agricultural productivity: Ozone pollution can damage crops and reduce yields.
• Acid Rain: Sulfur and nitrogen emissions lead to acid rain, harming forests, lakes, and infrastructure.

These impacts show that increasing aerosols and pollutants have wide-ranging effects beyond climate warming alone.

Global Environmental Issues Summary

The final part of the lecture offered a broader context of global environmental challenges:

• Global Warming: rising temperatures, with consequences like extreme weather, sea-level rise.
• Water/Air/Land Pollution: chemical pollution, water contamination, and land pollution.
• Resource Depletion: Humanity is depleting natural resources – fossil fuels, fresh water, soil fertility, minerals, fish stocks.
• Ozone Depletion: thinning of the stratospheric ozone layer by CFCs (mitigated by the Montreal Protocol).
• Reduction of Biodiversity: Species are going extinct at a high rate due to habitat loss, climate change, pollution, invasive species, and overexploitation. This is sometimes called the sixth mass extinction event.

The concluding message ties climate change into a suite of global issues that all interconnect. It’s a call for understanding the broad impact of human activities on Earth’s systems.

May 12, 2025 – Coral Reefs and Climate Change Impacts

Background: Coral Reefs

Coral reefs are diverse underwater ecosystems built by reef-building corals, which are tiny animals (polyps) that secrete calcium carbonate skeletons. Reefs thrive in warm, shallow tropical oceans and are often called the “rainforests of the sea” for their high biodiversity – they provide habitat for roughly a third of all marine species. Reefs also protect coastlines from waves and support fisheries and tourism.

Climate Change Pressures on Reefs

Climate change and human activities are putting intense pressure on reef ecosystems. Key stressors include rising ocean temperatures, ocean acidification, pollution, and excessive sunlight/UV exposure.

• Rising ocean temperatures: The greatest threat is warming of sea water due to global climate change. Corals have a narrow temperature tolerance. When water gets even a few degrees Celsius above the usual summer maximum, corals become stressed.
• Coral Bleaching: This is a phenomenon where corals expel their symbiotic algae (zooxanthellae) under stress (often heat stress). Those algae live in coral tissues and give corals much of their color and, importantly, provide food via photosynthesis. When corals bleach, they turn white (“bleached”) because their white calcium skeleton shows through their transparent tissues after losing the pigmented algae. Bleaching is essentially the coral starving; if the stressful conditions persist or repeat frequently, the corals can die. Coral bleaching is a major sign of reef stress. The main cause of mass bleaching is increased sea temperature. Other local stressors can also cause corals to bleach: disease, sedimentation, changes in salinity, or severe storms.
• Ocean Acidification: This refers to the ocean absorbing excess CO₂ from the atmosphere, which lowers pH (makes seawater slightly more acidic). Acidification makes it harder for corals to deposit calcium carbonate skeletons.
• Pollution: This can be agricultural runoff causing algal overgrowth, sewage, or chemical pollution that harms corals. Pollution (along with overfishing) can upset the ecological balance, making reefs more susceptible to disease and algal domination.
• Excessive sunlight: High UV can further stress corals, especially if water quality is too clear or low winds lead to very calm water that overheats.

Recent Bleaching Events

The Great Barrier Reef (GBR) underwent its sixth mass bleaching event since 2016 during the summer of 2024–25. This unprecedented frequency means reefs do not have time to fully recover. Around 84% of the world’s coral reefs have been exposed to bleaching-level heat stress between January 2023 and April 2025, affecting at least 83 countries/territories. This indicates the current global bleaching event (2023-2025) is the most widespread on record. In 2024, the average annual sea surface temperature in non-polar oceans reached 20.87°C (69.57°F), which is extremely high by historical standards and beyond many corals’ comfort zone. These statistics underscore that climate change is happening now in our oceans, with record heat causing unprecedented coral damage.

Impacts of Bleaching

When corals bleach and potentially die, reef structures degrade. This leads to loss of habitat for fish and other reef organisms, reducing biodiversity. If enough of the reef dies, the structure can erode, compromising coastal protection.

Scientists and Communities Taking Action

Research and global efforts aim to understand bleaching and protect coral reefs for the future. Actions include:

• Monitoring and research: Organizations like NOAA’s Coral Reef Watch use satellites to monitor ocean heat stress and predict bleaching.
• Marine Protected Areas (MPAs): Many countries are establishing MPAs to reduce local stress on reefs.
• Restoration efforts: Coral farming involves growing corals in nurseries and then planting them onto degraded reefs to speed recovery. Artificial reefs can provide new surfaces for corals to colonize.
• Selective breeding or assisted evolution: Some projects try to breed or foster heat-resistant corals.

However, these efforts, while helpful locally, cannot by themselves counteract the global threat of warming seas; that ultimately requires reducing greenhouse gas emissions.

Deep Sea Corals and Ocean Impacts

Deep sea corals (and other deep ocean ecosystems) are also affected by climate change. Deep-sea corals live in cold, dark waters and do not have symbiotic algae, so they don’t bleach. However, they are affected by ocean warming, and as CO₂ acidifies the ocean, it becomes harder for them to build and maintain their calcium carbonate skeletons. So, deep-sea corals are suffering silently from climate change and acidification.

Human Impact on the Sea (Beyond Climate)

Other human impacts include:

• Overfishing: Removing too many fish disturbs the ecosystem balance. If herbivorous fish are overfished, algae can overgrow and smother corals.
• Pollution: Ranges from physical trash (like plastic) to chemicals. Plastics can entangle or be ingested by marine life. Chemical pollutants degrade water quality and reef health.

Climate change, overfishing, and pollution are a deadly trio for coral reefs. Mitigating these threats requires global action on carbon emissions and local action on conservation and pollution control.

Coral Reef Before-and-After

Slides showed a “Before and After” of coral reefs, illustrating a vibrant reef vs. a bleached/dead reef, driving home what is at stake. The current global bleaching event is the worst on record – truly “uncharted territory” for corals. The fear among scientists is that as warming continues, we could lose a majority of coral reefs within decades.

Hopeful Note

The presentation ended with the notion that people are taking action (reef restoration, international efforts). It underscores that while the situation is dire, increased awareness and scientific attention are being directed at saving what can be saved.

May 14, 2025 – Air Pollution: Sources, Effects, and Solutions

Sources of Air Pollution

This presentation addressed air pollution, going into causes, case studies, and mitigation. Sources are categorized into indoor vs. outdoor and natural vs. human-made:

• Indoor air pollution: Common indoor pollutants include cleaning agents, paints, and sprays that release VOCs (Volatile Organic Compounds). VOCs can off-gas from household products and cause health issues. Indoor pollution (like smoke from indoor cooking with wood/coal in developing countries) causes about 3.2 million deaths globally each year.
• Natural outdoor sources:
  • Volcanoes: Emit sulfur dioxide and ash, which can cause global cooling or severely affect local air quality.
  • Dust storms: Occur in dry regions and blow fine dust, worsening air quality over large areas.
  • Wildfires: Release a lot of pollutants: carbon dioxide, carbon monoxide, and PM2.5 (fine particulate matter). PM2.5 from wildfire smoke is a major health hazard.
• Anthropogenic outdoor sources: Include vehicles (cars, trucks emit NOx, CO, PM, and VOCs), industry and power plants (burn fossil fuels releasing SO₂, NOx, PM, heavy metals), agriculture (burning fields, livestock releasing ammonia, methane), and waste burning.

The distinction is that human activities have greatly increased the amount of pollutants and introduced some that are not significant naturally.

Effects of Air Pollution

Effects are broken down into Health effects and Environmental impacts.

• Health Effects:
  • Short-term: irritation of eyes, nose, throat; coughing; respiratory infections; headaches.
  • Long-term: extended exposure increases risk of asthma, lung cancer, cardiovascular diseases (heart attacks, strokes). Particulate matter, especially PM2.5, can penetrate deep and even enter the bloodstream.
  • About 7 million deaths yearly are linked to air pollution (WHO figure), making it one of the leading global health risks.
• Environmental Impacts:
  • Acid Rain: Pollutants like SO₂ and NOx can transform into sulfuric and nitric acid in the atmosphere and fall as acid rain. Acid rain acidifies soils and water bodies, damages forests, and erodes man-made structures.
  • Agricultural effects: Ground-level ozone (from smog) harms crops and reduces productivity.
  • Climate Change: Air pollutants include greenhouse gases (CO₂, methane) and others that contribute to global warming. Black carbon (soot) warms by absorbing sunlight. Certain pollutants drive climate change, linking these environmental issues together.

The overlap of air pollution and climate is significant; cutting fossil fuel use will both reduce harmful smog and reduce CO₂.

Case Studies of Cities

The presentation gave real-world case studies demonstrating air pollution issues and solutions:

• Delhi, India: Known for some of the world’s worst air quality, especially each winter, due to vehicle emissions, industrial smoke, and crop burning. In 2019, the AQI (Air Quality Index) exceeded 500 (“hazardous”). Measures include the “odd-even” car license plate system and temporary school closures.
• Los Angeles, USA: Historically (1950s-70s) had terrible smog due to many cars, industrial emissions, and geography that traps pollution. The introduction of catalytic converters on cars, cleaner fuel requirements, and the U.S. Clean Air Act regulations led to dramatic improvements. LA still struggles with ozone on hot days but is a success story in policy and technology.
• Beijing, China: Before the 2008 Olympics, Beijing’s air was extremely polluted. The government took drastic temporary measures (closing factories, restricting cars) and invested in public transport. Beijing’s air has improved significantly due to sustained policies (including nationwide coal power plant emission controls).

These case studies highlight that policy and technology can make huge differences. Developed countries largely cleaned up worst pollution in the latter 20th century, and developing countries are now working on it.

Solutions and Actions

Solutions at individual and community levels:

• Individual Actions: Use clean energy at home (solar panels, green power). Monitor local air quality and avoid strenuous outdoor activity on bad air days.
• Community & School Actions: Organize tree planting or green space restoration. Start or join environmental clubs to raise awareness and push schools to adopt greener practices. Work with local leaders to advocate for clean air policies and anti-idling zones near schools. Promote carpooling or no-drive days.

These grassroots efforts complement government policies. Recent U.S. policy includes the EPA’s 2024 updated particulate standards, the 2022 Inflation Reduction Act, and the EPA 2023 Good Neighbor Plan for cross-state ozone pollution. Air pollution is a solvable problem with known technology and policy, and efforts often align with climate change mitigation.