AP Environmental Science Unit 9 Study Guide

The Ozone Layer 

Ozone: A form of oxygen, O₃. Good ozone is in the stratosphere and traps and absorbs UV rays from the sun, protecting humans from cell damage and cancer. Bad ozone is produced in the troposphere and is a pollutant that leads to lung damage. 

Ozone Hole: There is significant thinning of the ozone layer over Antarctica because of polar stratospheric clouds that form in Antarctica because of the extremely cold temperatures during the Antarctic winter, providing surfaces for chemical reactions involving chlorine. 

Chlorofluorocarbons (CFCs): These are nontoxic, stable molecules that contain chlorine, fluorine, and carbon and are used in refrigerants, propellants, foam, and packing materials. 

Relevance: CFCs break down the ozone as when they are emitted in the atmosphere, UV rays cause a chlorine atom to break away from the CFC molecule which is highly reactive. The free chlorine reacts with ozone molecules, pulling away one oxygen atom from an ozone molecule; this yields ClO and O₂. The ClO molecules hit and react with other ozone molecules, yielding a free chlorine and 2O₂. So, in short, CFCs reduce the ozone which is bad as more UV rays will be being emitted to earth’s surface. 

Montreal Protocol: International agreement that banned the usage of CFCs. So, people started using replacements like HCFCs, HFCs, and HFOs which didn’t affect the ozone. Effective. 

Greenhouse Gasses (GHGs)

Background: Short wave, high energy UV rays from the sun are absorbed by ozone molecules; UV rays do not affect temperature. Temperature is dependent on the trapping of longwave, low energy infrared radiation emitted from the Earth’s surface. The “trapping” is done by GHGs. 

GHGs: Gasses that trap outgoing IR from the Earth’s surface - water vapor, carbon dioxide, methane, nitrous oxide, ozone, CFCs. 

Greenhouse Gas Effect: Occurs when GHGs absorb and trap heat in the Earth's atmosphere, preventing it from escaping into space. This process keeps the planet warm enough to sustain life but can lead to global warming if greenhouse gas levels increase excessively (which it is). 

Water: While water vapor is a greenhouse gas, it has a low residence time in the atmosphere (it turns into a liquid quickly), so it does not drive atmospheric temperature change. 

Global Warming Potential (GWP): Measure of how much a molecule can contribute to global warming over 100 years relative to a molecule of carbon dioxide. 

• How well does it absorb IR?

• How long does it persist in the atmosphere (resident time)? 

If you take GWP and combine it with the concentration, you can truly get the total effect. 

While HFCs and HCFCs were good replacements for CFCs in regards to ozone depletion, their GWP is still really high. Only HFOs have low GWP and low ODP (Ozone Depleting Potential). 

Carbon Dioxide: Has the largest total effect because of its high concentration. 

Anthropogenic Sources of Carbon Dioxide 

• Burning of fossil fuels

• Land use changes (deforestation)

• Industrial processes, vehicle emissions 

Anthropogenic Sources of Nitrous Oxide 

• Synthetic fertilizers and agricultural soils 

• Burning of fossil fuels

Anthropogenic Sources of Methane

• Drilling and distribution of fossil fuels

• Livestock 

• Landfills (aerobic decomposition)

Anthropogenic Sources of CFCs 

• Aerosol propellants 

• Refrigerants, foams  

Historic Climate Change 

Were There Changes Before: Yes, the earth’s climate changed in the past due to variations in the earth’s orbit around the sun. 

Obliquity: Tilt of Earth’s axis, which affects the intensity and distribution of sunlight, driving seasonal variations and influencing ice ages over tens of thousands of years.

Eccentricity: Shape of Earth’s orbit around the Sun, ranging from more circular to elliptical, which alters the amount of solar energy reaching Earth and contributes to long-term climate cycles.

These factors lead to predictable variation in the Earth’s climate called Milankovitch Cycles. 

Carbon Dioxide, Temperature Relationship: There is a historical, direct relationship between concentrations of carbon dioxide on the earth’s surface temperature. However, now, the concentration of carbon dioxide in the atmosphere has increased exponentially due to anthropogenic activities. 

Measuring Historical Carbon Dioxide Levels: This was done by analyzing ice cores, sediments, tree rings, and carbon bands. 

• Ice Cores: Provide data from 800K years ago due to bubbles trapped each year as layers of ice laid down. 

• Sediments: Different species prefer different temperatures. The Foraminifera species fossilizes very well and is found in sedimentary layers of the ocean floor. Analysis can tell the rough temperatures over millions of years based on the presence and abundance of different Foraminifera species.

• Coral Bands and Tree Rings: These are not as reliable but can still give data. 

Keeling Curve

This curve shows carbon dioxide measurements from Hawaii and was the first to accurately measure carbon dioxide. It showed how carbon dioxide levels vary seasonally and are increasing overall. The seasonal variation is due less photosynthesis occurring in the winter, leading to higher carbon dioxide levels then. 

Global Warming and Climate Change

Global Warming: Long-term increase in Earth's average surface temperature due to rising levels of greenhouse gases in the atmosphere. 

Weather v. Climate: Weather refers to the short-term atmospheric conditions in a specific place, while climate describes the long-term average patterns of weather over a region.

Global Warming (increase in average temperature) -> global climate change (change in temperatures, precipitation, wind, storms, currents) -> global change (changes in soil, oceans, life, air, atmosphere, humans) 

Effects of Global Warming 

Increased Heat Waves

Human Effects: Heatwaves are more likely due to global warming, increasing the risk of death for outdoor workers, the poor, the elderly, and the homeless. There will also be an increased energy demand, requiring us to burn more fossil fuels. 

Agricultural Effects: There will be more damage to crops and increased irrigation needs. 

Impact on Polar Vortex 

Polar Vortex: Large area of low-pressure, cold air that circulates around the poles, keeping frigid air contained in the Arctic region.

Effect: Rising temperatures weaken the vortex, causing it to wobble and spill icy Arctic air into lower latitudes, triggering extreme cold spells in unexpected regions.

Faster Warming of Polar Regions 

Unequal Warming: Polar regions of the earth are warming faster than other regions in a phenomenon known as polar/artic amplification. 

Albedo: Since the polar regions are filled with snow and ice, they have a very high albedo (can reflect sunlight); however, as the ice and snow melt, there is more exposed ocean water with lower albedoes, absorbing more heat. This is why there’s polar amplification in these regions. 

Effects: This leads to habitat loss for polar bears and algae. Seals use ice for resting and finding holes for breathing while polar bears use ice for hunting seals at breathing holes, so it disrupts this food chain. 

Melting of Permafrost 

Permafrost: Any type of soil, sediment, or rock that has been frozen continuously for a minimum of two years. 25% of the Northern Hemisphere is permafrost. 

Effects: As permafrost melts, organic matter trapped in the performance decomposes in the absence of oxygen forming methane gas. Also, there is more erosion with loss of structural support for buildings. 

Sea Temperature Rise 

Coral Bleaching: Higher water temperatures lead to coral bleaching, which occurs when stressed corals expel the symbiotic algae (zooxanthellae) that provide them with energy and color, leaving the corals white and vulnerable to starvation and disease.

Less Oxygen: Warmer water temperatures reduce the amount of dissolved oxygen leading to fish die-offs. 

Sea Level Rise

Thermal Expansion: Because of global warming, water temperatures are rising and water molecules move slightly further apart when they’re heated, leading to thermal expansion. 

Melting Ice Sheets and Glacier Ice: Land-based, continental ice sheets melt due to warming and the water flows into the ocean and leads to sea level rise. 

Effects: This leads to flooding of coastal ecosystems like estuaries and loss of habitat due to the melting of continental ice sheets. Increased floodings can lead to high insurance and repair costs and property loss. 100 million people live within 3 ft of the sea level, so there will be forced migration. 

Ocean Acidification 

Direct Exchange: With increased carbon dioxide in the atmosphere, there is increased carbon dioxide in the ocean. 

Formation of Carbonic Acid: Carbon dioxide combines with ocean water to from carbonic acid which dissociates into bicarbonate and H⁺ ions, which decreases the pH (more acidic). 

Effects: Marine organism that make shells use calcium ions and carbonate ions to build their calcium carbonate shells (calcification). However, the dissociated H⁺ ions bond with the carbonate ions, stealing it from the calcium and making bicarbonate ions. 

Impact on Atmospheric Currents 

Jets Streams: Global warming weakens the temperature gradient between the poles and the equator, disrupting jet streams, which can cause them to meander, leading to extreme weather patterns.

Hadley Cells: Global warming expands Hadley cells, pushing subtropical dry zones further poleward and intensifying droughts in some regions.

Increased Spread of Disease 

Disease Vectors: Living organisms (mosquitoes, fleas, ticks) that can transmit diseases from human to human or animal to human. 

Expanded Range: Warmer temperatures allow insect-transmitted diseases to spread to parts of the world previously too cold. 

Positive and Negative Feedback Loops 

Positive Feedback Loops: Climate change involves positive feedback loops that amplify changes, pushing the system further from its equilibrium state and making it increasingly unstable. Closed loop. 

• Warming → Melting ice → Reduced albedo (less sunlight reflected) → More heat absorbed → Warming

• Warming → Thawing permafrost → Release of stored methane and CO₂ → Increased greenhouse gases → Further warming

Negative Feedback Loops: These dampen or buffer changes, holding a system to some equilibrium state and make it more stable. Open loop. 

• Warming → More evaporation → Increased cloud cover → Clouds reflect more sunlight → Reduced warming

• As carbon dioxide levels in the atmosphere rise → Enhanced plant growth (CO₂ fertilization effect) → Less carbon dioxide (GHG) → less warming 

Kyoto Protocol and Paris Climate Agreement 

Kyoto Protocol: Set goals for global emissions of GHGs to be reduced by 2012. However, US (senate rejected) and China (developing country at that time) were not included, so the protocol was ineffective. 

Paris Climate Agreement: In 2015, this was signed by 197 countries and required all countries to do their part to slash greenhouse gas emissions. This was successful.