Welcome to Unit 9: Global Change!
In this final unit of AP Environmental Science, we look at the "Big Picture." We’ve spent the year talking about local ecosystems and specific pollutants, but now we are looking at how human activities are changing the entire planet. We will cover everything from the hole in the ozone layer to the warming of our oceans and the loss of biodiversity. Don't worry if it feels like a lot of information—we will break it down into simple, manageable pieces!
9.1 & 9.2: Stratospheric Ozone Depletion and Recovery
First, a very important distinction: Stratospheric Ozone is "good" ozone. It sits high up in the atmosphere and acts like a giant pair of sunglasses for the Earth, blocking harmful Ultraviolet (UV) radiation. This is different from "tropospheric ozone" (smog), which is "bad" and found near the ground.
How the "Hole" Happens
Human-made chemicals called Chlorofluorocarbons (CFCs) were once used in aerosol cans and refrigerators. When they reach the stratosphere, UV light breaks them apart, releasing a Chlorine (Cl) atom. This chlorine atom is like a "chemical bully"—it steals an oxygen atom from ozone (\( O_3 \)), turning it into regular oxygen (\( O_2 \)).
Why it's scary: One single chlorine atom can destroy 100,000 ozone molecules before it's finally removed from the atmosphere!
The Solution: The Montreal Protocol
The Montreal Protocol (1987) is the most successful environmental treaty in history. Countries agreed to phase out CFCs. We replaced them with HFCs (Hydrofluorocarbons).
Important Note: While HFCs don't destroy the ozone layer, they are very strong greenhouse gases. We solved one problem but accidentally contributed to another!
Quick Review:
• Good Ozone: Stratosphere (blocks UV).
• The Problem: CFCs release Chlorine.
• The Consequence: Skin cancer, cataracts, and damaged plant photosynthesis.
• The Fix: Montreal Protocol.
9.3 & 9.4: The Greenhouse Effect and Warming
The Greenhouse Effect is actually a natural process that keeps Earth warm enough for life. Think of it like a blanket. However, humans are adding "extra blankets," making the planet too hot.
How it Works (Step-by-Step)
1. High-energy solar radiation (visible light) enters the atmosphere.
2. The Earth absorbs this energy and re-radiates it as lower-energy Infrared radiation (heat).
3. Greenhouse Gases (GHGs) in the atmosphere absorb that heat and send it back toward the surface.
The Key Players (GHGs)
• Carbon Dioxide (\( CO_2 \)): Released by burning fossil fuels and deforestation. It's the most abundant GHG from human activity.
• Methane (\( CH_4 \)): Released from cows (belching), landfills, and natural gas leaks. It is much more "potent" than \( CO_2 \).
• Nitrous Oxide (\( N_2O \)): Comes primarily from agricultural fertilizers.
• Water Vapor (\( H_2O \)): A natural GHG, but it increases as the planet warms (a positive feedback loop).
• CFCs/HFCs: Human-made chemicals with the highest Global Warming Potential (GWP).
Memory Aid: Think of GWP as the "strength" of the gas. If \( CO_2 \) is a tiny match, a CFC molecule is a giant bonfire.
9.5: Global Climate Change
Climate change is the long-term shift in temperature and weather patterns. It’s not just "Global Warming"—it’s everything that follows.
Key Impacts to Know
• Sea Level Rise: This happens for two reasons. First, Thermal Expansion (water expands as it gets warmer). Second, the melting of land ice (glaciers and ice sheets).
• Disease Vectors: As the planet warms, insects like mosquitoes move into new, previously cold areas, bringing diseases like Malaria or Zika with them.
• Changing Biomes: Plants and animals must migrate toward the poles or higher altitudes to stay in their "comfort zone."
Common Mistake: Many students think melting sea ice (like the North Pole) raises sea levels. It doesn't! Think of an ice cube in a glass of water—when it melts, the level stays the same. It’s the ice on land (Greenland/Antarctica) that adds new water to the ocean.
9.6 & 9.7: Ocean Warming and Acidification
The ocean is the Earth’s "heat sink"—it has absorbed over 90% of the extra heat from global warming.
Ocean Warming
When the water gets too warm, corals get stressed and kick out the colorful algae living inside them. This is called Coral Bleaching. Without the algae, the coral loses its food source and can die.
Ocean Acidification
This is often called the "Evil Twin" of climate change. It is not caused by warming; it is caused by \( CO_2 \) directly.
The Chemistry: When \( CO_2 \) dissolves in the ocean, it reacts with water to form Carbonic Acid (\( H_2CO_3 \)).
\( CO_2 + H_2O \rightarrow H_2CO_3 \)
This lowers the pH of the water.
The Impact: Acidic water makes it very difficult for "calcifiers" (like clams, oysters, and corals) to build their shells because the acid "steals" the carbonate ions they need. Analogy: Imagine trying to build a brick house while someone keeps stealing your bricks!
9.8, 9.9, & 9.10: Biodiversity and Human Impact
We are currently living through what scientists call the Sixth Mass Extinction. Unlike previous ones, this one is caused by humans.
HIPPCO: The Drivers of Extinction
This is the most important mnemonic for this section. It lists the main reasons we are losing species:
H - Habitat Loss (The #1 cause! Destruction, fragmentation, or degradation).
I - Invasive Species (Non-native species that outcompete locals, like Kudzu or Lionfish).
P - Population Growth (More humans = more resources used).
P - Pollution (Trash, chemicals, noise, light).
C - Climate Change (Shifting habitats too fast for species to adapt).
O - Overexploitation (Overhunting, overfishing, or poaching).
Specialists vs. Generalists
When the environment changes, Specialists (like Pandas or Koalas) are the first to die because they have very specific needs. Generalists (like Raccoons or Rats) and Invasive Species usually survive and thrive because they can eat almost anything and live anywhere.
Legislation to Remember
• CITES: An international treaty that bans the trade of endangered species (parts or whole), like elephant ivory.
• Endangered Species Act (ESA): A U.S. law that protects species at risk of extinction and their habitats.
Key Takeaway: Protecting biodiversity isn't just about saving "cute animals"—it's about maintaining the Ecosystem Services (like clean water and pollination) that humans need to survive!
Final Quick Tips for the Unit
• Don't mix up Ozone and Climate Change! Ozone depletion is about UV radiation and CFCs. Climate change is about heat and GHGs like \( CO_2 \). They are two different problems!
• Think Logically: If you get a question about how a species will react to global change, ask yourself: Is it an r-selected generalist (likely to survive) or a K-selected specialist (likely to go extinct)?
• Positive Feedback Loops: Remember that warming leads to more warming (e.g., melting permafrost releases methane, which causes more warming).