9.5 Global Climate Change

Global climate change shifts both short term and long term conditions in ways that reshape ecosystems on land, in the ocean, and at the poles. In AP Environmental Science, you should be able to explain how warming changes sea level, ocean and air circulation, soil, and polar ice, and why the poles warm fastest because of positive feedback loops.

Expect diagrams and data, such as temperature or sea ice trends over time, that you have to read and explain in terms of the climate process behind them.

Feedback Loops Drive Faster Warming and Habitat Change

• Ice cores trap old air bubbles that let scientists track past CO2 levels and link high CO2 to warmer climates.
• The poles warm faster than the rest of the planet because of the ice-albedo positive feedback loop.
• Melting polar ice and snow means less solar energy reflected back to space, which causes even more warming.
• Thawing tundra and permafrost release methane, a greenhouse gas, speeding up climate change further.
• Climate change can shift atmospheric circulation (Hadley cells, jet stream) and ocean currents (the ocean conveyor belt), affecting climate especially in coastal regions.
• Sea level changes reshape marine habitats, creating some new shallow habitats on flooded shelves while pushing deeper communities out of the photic zone.

Heating and Cooling Climate Cycles

Earth has gone through large-scale climate shifts naturally over time. Scientists track past climate by studying CO2 trapped in ice cores. In very cold places, snowfall compacts and turns to ice. Tiny bubbles in that ice are samples of the atmosphere from when the snow first fell, so they can be analyzed for past levels of gases like carbon dioxide and methane.

Some ice in Antarctica is hundreds of thousands of years old. These samples reveal historic atmospheric CO2 concentrations, and periods of high CO2 line up with a warmer climate.

Earth naturally moves heat from the equator toward the poles through atmospheric and oceanic circulation. These currents carry warm water and air toward the poles and cooler water and air back toward the equator. Climate change can disrupt these patterns, which has large effects on global climate, especially in coastal regions.

Atmospheric and Ocean Circulation

Winds generated by atmospheric circulation help spread heat across the planet. As temperatures change, climate change may shift these circulation patterns, including Hadley cells and the jet stream.

Ocean currents, often described as the ocean conveyor belt, also carry heat around the world. When these currents change, the impact on global climate can be significant, and coastal regions tend to feel it most.

Soil Effects

Climate change affects soil through changes in temperature and rainfall. Shifts in these conditions can reduce soil viability and potentially increase erosion, especially where rainfall becomes more intense.

The Poles and Positive Feedback Loops

Polar regions respond faster to climate change than most of the planet. Ice and snow reflect the most energy back out to space, so when they melt, the change feeds on itself. This is the ice-albedo positive feedback loop.

Here is the cause-and-effect chain:

1. The poles warm and ice and snow start to melt.
2. Less solar energy is reflected by white surfaces back into space.
3. The darker land and ocean surfaces absorb more solar energy.
4. The poles warm even faster, melting more ice and snow.

The Arctic also has another feedback loop tied to thawing tundra and permafrost. As frozen ground thaws, previously frozen biomass decomposes and releases greenhouse gases like methane, which adds even more warming.

Losing ice and snow also removes habitat and food sources for species that depend on the ice, such as seals, walruses, and polar bears.

Sea Level and Marine Ecosystems

As polar ice melts, more water enters the ocean. Combined with the expansion of warming seawater, this raises sea level and can flood low-lying coastal areas.

Marine ecosystems respond to these sea level changes in mixed ways:

• Positive: Newly flooded continental shelves can create new shallow-water habitats.
• Negative: Deeper communities may end up below the photic zone, the sunlit layer of seawater where photosynthesis happens, and can no longer survive there.

Matching Causes to Effects and Explaining Climate Impacts

MCQ:

• Match cause to effect quickly. If a question describes melting ice leading to more absorbed sunlight and more warming, that is the ice-albedo positive feedback loop.
• Watch for vocabulary traps that swap climate change with ozone depletion. They are separate issues.

Free Response:

• When asked to explain an impact, write a full cause-and-effect chain rather than a single sentence. For example: warming melts ice, less sunlight is reflected, more is absorbed, the poles warm faster.
• If a prompt gives data or a graph, describe the trend first, then connect it to the climate process it shows.
• Be specific about which system you are discussing: atmospheric circulation (Hadley cells, jet stream), ocean currents (the ocean conveyor belt), soil, or polar ice.

Common Trap:

• Saying sea level rise is only harmful. The flooding of continental shelves can create new shallow marine habitats, even as deeper communities lose access to the photic zone. Show both sides when the question asks for impacts.

Common Misconceptions

• Misconception: Climate change and ozone depletion are the same thing.
  Actually: They are not. Climate change comes from excess greenhouse gases trapping heat, while ozone depletion involves chemicals like CFCs breaking down stratospheric ozone. Keep them separate.
• Misconception: Water vapor drives long-term climate change the way CO2 does.
  Actually: Water vapor is a greenhouse gas, but it has a short residence time and its concentration responds to temperature, so it acts as a feedback rather than the main driver of long-term human-caused climate change.
• Misconception: The whole planet warms at the same rate.
  Actually: The poles warm faster because of positive feedback loops involving melting ice and snow.
• Misconception: Sea level rise has only negative effects on marine life.
  Actually: Some flooded shelves create new habitat, while deeper communities can be pushed out of the sunlit photic zone.
• Misconception: A positive feedback loop is a good thing.
  Actually: Positive here means the change reinforces itself, not that the outcome is beneficial. The ice-albedo loop speeds up warming.

Related AP Environmental Science Guides

• 9.1 Stratospheric Ozone Depletion
• 9.3 The Greenhouse Effect
• Major Environmental Disasters
• 9.8 Invasive Species
• Unit 9 Review: Global Change
• 9.4 Increases in the Greenhouse Gases