Global Climate Change 1

Average Temperature of the Earth

Mechanism of the Greenhouse Effect

  • Absorption and re-emission of infrared radiation:

    • Water vapor absorbs and re-emits IR radiation

    • Comparison of Earth with an atmosphere and without an atmosphere

    • Temperature differences

Natural Greenhouse Gases (GHGs)

  • Natural GHGs effectively trap heat:

    • Primary GHG: Water vapor (H2O) contributes significantly to warming

    • Second most important: Carbon dioxide (CO2)

    • GHGs absorb solar radiation, creating a net warming effect

Earth’s Natural Energy Budget

  • Energy input versus energy output in Earth's climate system

Historic Temperature Changes

  • Earth's temperature changes over time:

    • Four glacial and interglacial periods every 100,000 years in the last 450,000 years

    • Milankovitch Cycles explain these temperature oscillations

Milankovitch Cycles and Their Effects

Changes in Eccentricity

  • Variations in Earth's orbit shape influence climate

  • Earth currently in low-eccentricity orbit

Changes in Obliquity

  • 41,000-year cycles of axial tilt

  • Low obliquity leads to increased sunlight at the Equator

Precession of Earth's Axis

  • 26,000-year cycles impacting seasonal climate dynamics

  • Influence of gravitational forces from other celestial bodies

Measurement of Historic Temperatures

Ice Core Analysis

  • Air bubbles in ice cores preserve historical atmospheric compositions

  • Analysis of trapped air provides estimates of past temperatures

Ocean Floor Sediment Analysis

  • Calcium carbonate shells from ocean sediments provide information on historical seawater temperatures

Recent Temperature Records

Types of Datasets for Temperature Measurement

  1. Surface Station Measurements

    • Over 7,500 stations gather temperature data near Earth's surface.

  2. Radiosonde Measurements

    • Balloon-based measurements at various altitudes twice daily

  3. Microwave Sounding Unit (MSU) Satellite

    • Provides temperature data from the lower atmosphere since 1979

Findings from Recent Temperature Records

  • Strong evidence of global warming observed through datasets;

  • Near-surface stations and radiosonde indicate warming;

  • Satellite data shows cooling in the upper stratosphere

Comparison of Recent and Historical Records

  • Current high temperatures, while not unprecedented, have increased at a higher rate than historical averages

  • Anthropogenic global warming characterized by rapid temperature increases driven by human activity and excess GHG emissions.