Climate Change

Science 123		Spring 2026
	Climate Change

Climate - what do we mean?

Temperature Record
- Surface Thermometer Record (1860 - present)
  - global average surface temperature increased by 0.4 - 0.8 degrees C in the 20th century
  - two distinct periods of increase: 1910 - 1945 and 1976 - present
  - the 1990s represent the warmest decade (current decade may be warmer yet)
  - warmest individual years : 2005, 1997, 2004, 2003, 2002
  - Decorah Temperature History
- Confidence - very strong
  - represents direct measurement of a climate variable
  - thermometer technology well known
- Weaknesses in the data
  - changes in how and where observations were made
  - some technical difficulties persist - e.g. bubbles in the thermometer
  - uneven surface distribution
- Proxy Data Records
  - ocean floor sediment
  - tree ring data
  - coral reef data
- Ice Core Record

Causes of Climate Change
- Natural Causes
  - Incoming solar radiation - earth's orbit
    - ellipticity (100,000+ year periodicity)
    - tilt (40,000 year periodicity)
    - procession (20,000 year periodicity)
  - Incoming solar radiation - sun spots (11 and 22 year periodicity)
  - composition of the earth's atmosphere
  - earth's surface
  - El Nino
  - volcanoes
  - ocean conveyor belts
  - plate movement
- Anthropogenic Causes

Feedback Effects

Solar Radiation : On average, over the surface of the earth : 164 Watts/m$^2$

Climate Sensitivity : 0.75 $\pm$ 0.25 degrees C per watt per square meter