APES 9.5 Global Climate Change

Evidence of Climate Variability

Natural Factors Affecting Climate

  • Earth's orbit is not fixed; it changes over time.

  • Key factors influencing orbit:

    • Eccentricity:

      • Describes the shape of Earth's orbit; varies from circular to elliptical.

      • Cycle duration: approximately 100,000 years.

      • Affects distance from the sun and therefore solar insulation.

    • Obliquity:

      • Refers to the tilt of Earth's axis.

      • Greater tilt results in more direct sunlight to northern latitudes, causing warmer periods and ice cap melting.

      • Less tilt leads to cooler periods and reduced insulation.

Milankovitch Cycles

  • Combination of eccentricity and obliquity affects Earth's climate.

  • Predictable cycles responsible for ice ages and warm periods over approximately 100,000-year intervals.

Lines of Evidence

  1. Foraminifera Shells:

    • Tiny ocean floor organisms provide sediment layers indicating historical temperatures based on species prevalence.

  2. Ice Core Air Bubbles:

    • Trapped air bubbles in ice cores allow scientists to measure historical carbon dioxide levels; layers represent different time periods.

  3. Oxygen Isotopes:

    • Analysis of oxygen-18 to oxygen-16 ratio helps determine historical temperatures; higher ratios suggest warmer periods.

Correlation Between CO2 and Temperature

  • Consistent patterns of temperature and CO2 levels over 800,000 years.

  • Increasing CO2 contributes to immediate warming; complex feedback between temperature and CO2.

  • Current CO2 levels are unprecedented in history, raising concerns.

Impacts of Climate Change

Global Warming

  • Continued increase in Earth’s average surface temperature expected.

  • Specific consequences for ecosystems:

    • Loss of Habitats:

      • Certain habitats may become too dry due to altered precipitation patterns.

    • Rapid Extinction Rates:

      • Current extinction rates exceed background rates; possibility of a sixth mass extinction.

    • Drought and Soil Desiccation:

      • Regions may experience prolonged drought conditions impacting agriculture and natural flora.

Rising Sea Levels

  • Caused by melting polar ice and thermal expansion.

  • Implications for marine and coastal ecosystems:

    • Coastal communities may face displacement.

    • Barrier Islands Loss:

      • Rising waters inundate barrier islands, losing habitat and protective functions.

Melting Permafrost

  • Leads to anaerobic decomposition releasing methane and CO2, creating positive feedback loops.

  • Contributes to further warming and permafrost melting.

Future Projections and Risks

Risks Associated with 2°C Increase

  • Predicted by IPCC for 2100:

    • High threat to ecosystems and significant risks including:

      • Extreme weather events.

      • Coastal flooding.

      • Coral die-off and bleaching.

Impacts on Coastal Communities

  • Wealthier areas may construct barriers, but many low-income communities may displace due to rising sea levels.

  • Loss of barrier islands affects shoreline protection and habitats.

Changes in Atmospheric Circulation

Hadley Cell Changes

  • Expected to weaken and expand due to reduced temperature differential between poles and equator.

  • Consequences include:

    • Shift in subtropical weather patterns leading to dryness throughout 30-60° ranges.

Polar Jet Stream Implications

  • Weakened polar jet stream due to decreased temperature differential leads to erratic weather patterns.

  • Notable effects:

    • Unusual weather events such as the polar vortex of 2014 linked to destabilized jet stream.

Impact of Climate Change on Marine Ecosystems

  • Expansion of Marine Ecosystems

    • Rising sea levels flood low-lying coastal areas, transforming them into aquatic ecosystems.

    • This leads to an expansion of ranges for certain organisms that can thrive in new marine environments.

  • Shifting Photric Zone

    • The photic zone, which is the layer of the ocean where sunlight penetrates, will shift with rising sea levels.

    • Areas that become too deep will no longer receive sunlight, forcing reliant organisms (like producers) to migrate upwards in the water column.

  • Altered Ranges of Organisms

    • Many species, especially fish, will be forced to migrate towards cooler waters to find optimal conditions for oxygen and temperature.

    • Fishery Impact

      • The maximum sustainable yield (MSY) for several fish species may decline due to increased water temperatures and decreased oxygen levels.

Impact on Thermohaline Circulation

  • Understanding Thermohaline Circulation

    • This is the global movement of warm and cold water, crucial for distributing heat, nutrients, and oxygen throughout the oceans.

    • Warm water expands and moves away from the equator, while cold, salty water sinks at the poles.

  • Disruption from Climate Change

    • Melting ice from the Greenland ice sheets introduces cold fresh water into the North Atlantic, preventing the normal sinking of denser salt water.

      • This disrupts the thermohaline circulation and impacts nutrient and heat distribution globally.

    • Potential Consequences

      • Colder weather in Europe, which relies on the Gulf Stream for warmth.

      • Stopped cycling of nutrients and oxygen throughout oceans.

Polar Warming and Polar Amplification

  • Polar Regions Warming Faster

    • Polar Amplification: Refers to the phenomenon where polar regions experience more pronounced warming effects compared to the rest of the Earth.

    • Reasons for Polar Amplification

    1. Geographical Consideration:

      • More landmass in the Northern Hemisphere compared to the Southern Hemisphere, leading to increased heat transfer to ice.

    2. Albedo Effect:

      • Ice and snow reflect sunlight, while open ocean absorbs heat. Melting ice exposes more ocean, absorbing more heat (positive feedback loop).

    3. Thermohaline Circulation:

      • Warm water from the equator is transferred to both poles, contributing to warming effects in polar regions.

  • Impact of Soot and Pollution

    • Particulate matter like soot decreases the albedo effect of ice, causing it to absorb more heat and accelerate melting.

Impacts on Polar Ecosystems

  • Loss of Habitat

    • Melting Arctic ice reduces habitats available for animals, disrupting their feeding and resting behaviors.

    • Example: Seals

      • Depend on ice for resting and hunting.

  • Importance of Algae in Polar Regions

    • Algae use ice as a substrate, performing crucial roles at the base of the food web; ice loss diminishes these habitats.

  • Challenges for Polar Bears

    • Depend on ice to hunt seals; with less ice, they face increased difficulty in locating and capturing prey.