AP Environmental Science Unit 9: Global Change Exhaustive Study Guide

Stratospheric Ozone: Formation and Importance

• Stratospheric ozone is referred to as the "good" kind of ozone ($O_3$).
• It resides in the stratosphere to absorb dangerous, high-energy ultraviolet (UV) radiation from the sun.
• UV radiation is the same type of radiation responsible for causing sunburns and can lead to skin cancer and eye damage over long-term exposure.
• Because of these risks, humans utilize sunblock and other protective measures.
• The formation of ozone involves a specific chemical reaction:
  • UV radiation strikes oxygen molecules ($O_2$).
  • This collision splits the $O_2$ molecule into two individual atmospheric oxygen atoms ($O$).
  • One of these single atmospheric oxygen atoms ($O$) then reacts with another oxygen molecule ($O_2$).
  • The result of this reaction is the formation of the ozone molecule: $O + O_2 \rightarrow O_3$.

Ozone Depletion and Chlorofluorocarbons (CFCs)

• Ozone depletion is considered a serious climate change issue that was first discovered in 1985.
• Scientists identified a "hole" or a significant thinning of the ozone layer over the Antarctic pole (the South Pole).
• This thinning occurs on a seasonal basis and is driven by anthropogenic (man-made) chemicals.
• The primary chemicals causing depletion belong to the halogen family, including:
  • Chlorine ($Cl$)
  • Fluorine ($F$)
  • Bromine ($Br$)
• Chlorine is the major damaging component of Concern, found primarily in Chlorofluorocarbons ($CFCs$).
• Sources of $CFCs$ include:
  • Aerosol propellants
  • Refrigerants
  • Manufacturing processes
• The chemical mechanism for ozone destruction is as follows:
  • UV radiation causes $CFCs$ to decompose, releasing a chlorine ($Cl$) atom.
  • The chlorine reacts with ozone: $Cl + O_3 \rightarrow ClO + O_2$.
  • The resulting chlorine monoxide ($ClO$) is unstable and continues to react with other ozone molecules.
  • This reaction breaks ozone down into standard oxygen: $ClO + O_3 \rightarrow Cl + 2O_2$.
  • This process regenerates the chlorine atom, allowing it to continue the cycle of destroying more ozone molecules.

International Agreements and Substitutes for CFCs

• The Montreal Protocol was written in the 1980s to protect the stratospheric ozone layer from further depletion.
• It aimed to phase out the production and use of $CFCs$ and replace them with less harmful chemicals.
• One primary replacement is Hydrofluorocarbons ($HFCs$).
• Characteristics of $HFCs$:
  • They do not cause ozone depletion because they lack chlorine.
  • However, they are exceptionally strong greenhouse gases that contribute to heat retention in the atmosphere.
• Protecting the ozone layer is vital for human and animal health to reduce the incidence of:
  • Sunburns
  • Skin damage and skin cancer
  • Eye damage, specifically cataracts.

The Greenhouse Effect and Greenhouse Gases

• The greenhouse effect is a naturally occurring process that is necessary to keep the Earth warm and hospitable for life.
• The Process:
  • Heat from the sun enters the atmosphere in the form of infrared radiation.
  • While some heat reflects back into space, greenhouse gases trap a portion of this heat within the atmosphere, warming the planet's surface.
• Problematic warming occurs when the concentration of greenhouse gases increases due to anthropogenic activities, primarily fossil fuel combustion.
• The Kyoto Protocol is an international agreement specifically designed to address the greenhouse effect by reducing greenhouse gas emissions worldwide.
• Major Greenhouse Gases and their properties:
  • Water Vapor ($H_2O$): Very low warming potential; cycles quickly through the atmosphere via the hydrologic cycle (precipitation and evaporation).
  • Carbon Dioxide ($CO_2$): The baseline for measuring other gases; has a Global Warming Potential (GWP) of $1$. It is released in massive quantities from burning fossil fuels.
  • Methane ($CH_4$): Significantly stronger warming potential than $CO_2$.
  • Nitrous Oxide ($N_2O$): Much stronger warming potential than methane.
  • $CFCs$: Possess the highest warming potential and can remain in the atmosphere for a very long time.

Global Warming Trends and Regional Impacts

• Global warming is the result of the intensification of the greenhouse effect.
• Carbon dioxide levels are monitored at locations like the Mauna Loa Observatory in Hawaii.
• $CO_2$ levels show a seasonal zigzag trend:
  • Levels drop when plants are highly productive and performing photosynthesis.
  • Levels rise when plants are dormant and not removing as much $CO_2$ from the air.
• Despite seasonal fluctuations, the overall trend is a steady increase, correlating with human fossil fuel use and the net destruction of vegetation (deforestation).
• Global temperatures are also increasing, but not evenly across the globe.
• Extreme northern latitudes, such as the North Pole, are warming faster than other regions, with temperature changes ranging from $1\,^{\circ}C$ to $4\,^{\circ}C$.

Positive Feedback Loops in Polar Regions

• Positive feedback loops are cycles of activity that encourage and accelerate the warming effect over time.
• Feedback Loop 1: Permafrost Thawing
  • Increasing temperatures cause the thawing of tundra permafrost (permanently frozen ground).
  • Thawing releases trapped methane ($CH_4$), a potent greenhouse gas.
  • Methane leads to more warming, which causes more thawing, creating a self-reinforcing cycle.
• Feedback Loop 2: Albedo and Ice Melt
  • Ice and snow have a high albedo, meaning they reflect most incoming solar heat back to space.
  • As ice melts, it exposes ocean water, which has a low albedo and absorbs heat from the sun.
  • This absorption increases water temperature, leading to more ice melt and further warming.

Broad Effects of Climate Change on Biodiversity and Geography

• Loss of Habitat: Melting ice reduces hunting grounds for species like polar bears.
• Species Migration: Biomes (like tropical rainforests or savannas) are spreading north and south away from the equator. Species move to follow these changing habitats or to escape increasing heat.
• Disease Spread: Disease vectors like mosquitoes are spreading into new northern and southern territories as temperatures rise.
• Soil Productivity: Changes in temperature and moisture affect the ability of soil to support agriculture.
• Ocean and Wind Currents: Climate change can cause shifts in global circulation patterns.
• Sea Level Rise: Caused by the melting of glaciers/ice caps and thermal expansion.
• Thermal Expansion: As water molecules ($H_2O$) get warmer, they gain more energy and move faster. This causes the molecules to move further apart, increasing the total volume of the ocean.

Ocean Warming and Acidification

• Ocean Warming: The ocean has a high heat capacity and absorbs much of the heat trapped by greenhouse gases.
  • This leads to metabolic and reproductive changes in marine species.
  • It causes coral bleaching, where the symbiotic algae living in coral leave or die, leaving the coral white.
• Ocean Acidification: Caused specifically by the absorption of atmospheric $CO_2$.
  • The chemical reaction: $CO_2 + H_2O \rightarrow H_2CO_3$ (Carbonic Acid).
  • Increased acidity lowers the ocean's pH.
  • Carbonic acid reacts with carbonate ions, effectively "stealing" them from shelled organisms.
  • Organisms that need carbonate to build their shells are unable to grow or maintain their structures in highly acidic water.

Biodiversity Loss and the HIPPCO Framework

• The major factors causing biodiversity loss can be remembered via the acronym HIPPCO:
  • H: Habitat destruction (including fragmentation).
  • I: Invasive species (which outcompete native species).
  • P: Population growth of humans.
  • P: Pollution (air and water pollution).
  • C: Climate change.
  • O: Over-exploitation (over-fishing, poaching, and trade of species).
• These factors lead to species becoming threatened or endangered, putting them at high risk of extinction.
• Traits of endangered species:
  • Often specialist species (picky about diet and habitat).
  • Easily outcompeted by invasive generalists.
  • Have very specific habitat requirements.

Legislative and Practical Methods for Protecting Biodiversity

• Endangered Species Act (USA): A domestic law that creates a list of protected species and protects their habitats from harm.
• CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora): An international agreement to regulate the trade of plants and animals to ensure it is not detrimental to their populations.
• Practical Protection Strategies:
  • Criminalizing poaching to discourage illegal hunting.
  • Protecting existing habitats.
  • Installing habitat corridors to connect fragmented areas (e.g., across roads/neighborhoods).
  • Reintroduction programs (e.g., gray wolves in Yellowstone National Park).
  • Sustainable land use monitoring.
  • Breeding programs in zoos.
  • Restoring compromised or lost ecosystems.
  • Reducing non-native/invasive species that compete with native specialists.