Topic 9.5 Notes – Global Climate Change

What Global Climate Change Is

Climate is the long-term pattern of conditions in a region. Weather is what happens over short periods like a day or a week. A snowstorm or cold snap does not cancel climate change because climate is about trends over time.

Global climate change includes shifts in:

• Temperature
• Precipitation
• Winds
• Ocean circulation
• Ice cover
• Sea level

Earth’s climate has always changed over geologic time. Past warming and cooling happened because of things like:

• Orbital changes in Earth’s path and tilt
• Solar variation in energy from the sun
• Volcanism that can cool climate by adding reflective particles
• Tectonics that move continents and reshape oceans
• Atmospheric composition changes, especially greenhouse gases

Today’s climate change sits on top of that natural variability, but the current shift is strongly tied to rapid increases in greenhouse gases from human activity. One of the biggest tested ideas here is that global change does not mean uniform change. The atmosphere and oceans redistribute heat and moisture, so some regions get warmer faster, wetter, drier, or stormier than others.

Evidence of Climate Change Through Time

A lot of past climate evidence comes from proxy records, which are indirect clues about earlier conditions.

Ice cores

Ice cores drilled from Greenland and Antarctica preserve yearly layers of snowfall. Tiny trapped air bubbles act like samples of ancient atmosphere.

Air bubbles in an ice core

Ice cores let scientists measure:

• Past CO$_2$ levels
• Past methane levels
• Past temperatures using isotopic and chemical data

These records show repeated glacial and interglacial cycles over hundreds of thousands of years. On graphs, CO$_2$ and temperature usually rise and fall together.

What AP loves you to notice from a graph:

1. Identify the pattern over time
   Example: CO$_2$ increases sharply near the present.
2. Connect it to a climate process
   More greenhouse gases strengthen heat trapping.
3. Explain the consequence
   Warmer temperatures melt ice, shift habitats, and raise sea level.

The major conclusion is not just “climate changed naturally before.” It is that recent CO$_2$ increase is much more rapid than the older natural swings shown in long records.

If they ask for percent change, use

$$\text{Percent change}=\frac{\text{new}-\text{original}}{\text{original}}\times 100$$

Major Physical Changes and Their Ecosystem Effects

Rising temperatures and cryosphere change

The cryosphere means Earth’s frozen water, including snow, glaciers, sea ice, and permafrost. As temperatures rise, more of it melts.

Important distinction:

• Melting land ice raises sea level
• Melting floating sea ice has little direct effect on sea level

Sea ice still matters a lot because it affects albedo and provides habitat.

Sea-level rise and marine habitats

Sea level rises because of:

• Melting land ice
• Thermal expansion of warmer seawater

Effects on coasts include:

• More flooding
• More erosion
• Saltwater intrusion into freshwater supplies
• Displacement of coastal populations

Marine ecosystems can be affected in two directions:

• Positive
  Newly flooded continental shelves can create new shallow habitats.
• Negative
  Benthic communities may end up below the photic zone, the sunlit layer where photosynthesis can happen.

Soil impacts

Climate change also changes soil by altering temperature and rainfall.

• Higher temperatures can increase evaporation and dry soils.
• Vegetation loss removes roots that hold soil in place.
• Heavier rain can increase runoff and strip away topsoil even if yearly rainfall stays similar.

How Heat Redistribution Changes Regional Climate

Atmospheric and ocean circulation move heat around the planet. That is why a global shift changes regions differently.

Atmospheric circulation

Hadley cells are large tropical circulation patterns that help set up wet equatorial zones and dry subtropical zones. Climate change can shift their position, width, or strength, which shifts rainfall belts too.

The jet stream can also change as temperature gradients change. That can redirect storm tracks and change regional temperature and precipitation.

Global atmospheric circulation

Ocean conveyor belt

The ocean conveyor belt is global circulation driven by surface currents and deep thermohaline circulation, which depends on temperature and salinity.

If warming and freshwater from melting land ice reduce water density in the North Atlantic, sinking can weaken. That means less heat may be delivered to nearby coasts, including parts of Europe, even as global average temperature continues rising.

Global ocean conveyor belt

Why the Arctic Changes Faster

This is polar amplification. The Arctic warms faster than the global average because positive feedback loops strengthen the original warming.

Ice-albedo feedback

1. Snow and ice reflect lots of sunlight because they have high albedo.
2. Warming melts ice.
3. Darker land or ocean is exposed.
4. Darker surfaces absorb more solar energy.
5. More absorption causes more warming and more melting.

The diagram below shows that self-reinforcing cycle.

Ice-albedo positive feedback loop

Permafrost feedback

Permafrost is ground frozen for at least two consecutive years.

1. Rising temperature thaws permafrost.
2. Frozen organic matter starts decomposing.
3. Decomposition releases CO$_2$ and methane.
4. Those greenhouse gases increase warming.
5. More warming causes more thawing.

Polar ecosystem effects

Species that rely on ice lose habitat and food access. The course specifically expects polar bears, seals, and walruses.

Sea-ice loss can disrupt:

• Hunting
• Breeding
• Resting
• Migration
• Food-web timing