Methods for Measuring Past and Present Atmospheric Changes

Understanding how Earth’s atmosphere and climate have changed requires a range of scientific techniques, from ancient ice cores to real-time satellite monitoring. VCE Environmental Science requires knowledge of three key methods: ice core sampling, palaeoclimate records and direct atmospheric and ocean monitoring.

Ice Core Sampling

What Are Ice Cores?

Ice cores are cylindrical samples drilled from the ice sheets of Antarctica and Greenland. They are among the most powerful archives of past climate because:
- Snow layers accumulate year by year, preserving a continuous record
- Air bubbles trapped in the ice contain ancient atmosphere samples
- Chemical and physical properties of ice preserve temperature signals

What Ice Cores Record

Time Range and Resolution

• Antarctic ice cores (e.g. EPICA Dome C): Record extends back ~800,000 years
• Greenland ice cores (e.g. GRIP, GISP2): Higher temporal resolution but shorter record (~130,000 years)
• Annual layers visible in upper sections; resolution decreases with depth (ice flow compresses layers)

Key Finding

Ice cores demonstrate that current CO$_2$ levels (>420 ppm) are unprecedented in at least 800,000 years. During this period, CO$_2$ oscillated between ~180 ppm (glacial periods) and ~280 ppm (interglacials) — human emissions have pushed concentrations far above the natural range.

Palaeoclimate Records

Palaeoclimatology reconstructs past climates from multiple biological and geological proxies:

Limitations of Palaeoclimate Records

• Proxy uncertainty: Indirect measures may be influenced by multiple factors
• Incomplete records: Not all regions preserve high-quality proxy archives
• Calibration required: Proxies must be calibrated against instrumental records for accuracy
• Dating uncertainty: Some records have imprecise chronologies

Direct Atmospheric Monitoring

Instrumental Temperature Records

• Global land and ocean surface temperature records extend back to ~1850 (limited to ~1880 for reliable global coverage)
• Thousands of land-based weather stations provide daily maximum and minimum temperatures
• Records show global average surface temperature increased by ~1.1°C above pre-industrial baseline

Keeling Curve — CO$_2$ Monitoring

• Continuous CO$_2$ measurement at Mauna Loa Observatory, Hawaii since 1958 (Charles Keeling)
• Shows both annual seasonal cycle and long-term rising trend
• Currently records >420 ppm (2024), up from 315 ppm in 1958

Satellite Monitoring

• Earth-observation satellites measure land surface temperature, sea surface temperature, ice extent, snow cover, sea level, and atmospheric gas concentrations
• Provide truly global coverage since ~1979
• GRACE satellite: Measures ice sheet and glacier mass loss through changes in gravitational field
• OCO-2 satellite: Measures atmospheric CO$_2$ distribution globally

Ocean Temperature Monitoring

• Ship-based measurements: Historically taken with buckets (19th century) to thermometers mounted on ship hulls
• Argo floats: ~3,900 autonomous profiling floats drift globally, measuring temperature and salinity to 2,000 m depth
• Ocean heat content has increased substantially since the 1970s — oceans have absorbed ~90% of the excess heat from enhanced greenhouse effect
• Sea surface temperature (SST) records: Key indicator of El Niño/La Niña cycles and coral bleaching risk

Integrating Multiple Lines of Evidence

Climate scientists use multiple independent lines of evidence to detect and attribute climate change:

VCAA FOCUS: Exam questions may describe a climate measurement method and ask what it measures and what its limitations are. Focus on distinguishing between direct measurements (temperature, gas concentration) and proxy records (tree rings, ice cores), and always acknowledge limitations.