Ice cores from Antarctica and Greenland have been used to map the correlation between atmospheric greenhouse gases and atmospheric temperatures over (up to) the last 800,000 years.
The greenhouse gas (Carbon Dioxide (CO2) and Methane (CH4)) levels can be measured directly from the air bubbles trapped in the ice. Historical temperatures can be measured indirectly using a mass spectrometer to measure the ratios of the heavier non-radioactive isotopes of Hydrogen (2H) and Oxygen (18O) to the lighter (and more common) non-radioactive isotopes of Hydrogen (1H) and Oxygen (16O) in the melted ice (H2O).
There is less 2H and 18O when it is colder and more 2H and 18O when it is warmer. Seasonal oscillations in the 2H and 18O levels along the depth of the ice core are used to identify the sections of ice core belonging to each year, going back in time.
For the modern period, where temperatures and greenhouse gas have been measured directly from the atmosphere, the direct data matches the data from the ice cores.
The absolute level and the rapid rate of increase of greenhouse gases in the atmosphere (and the associated increase in temperature) during the last 200 years have no precedent in the last 800,000 years. The modern human industrial era (the last 200 years) is characterised by the burning of fossil fuels which creates the greenhouse gas CO2.
NASA satellites, using distance measuring lasers, have measured the net amount of ice that has melted in Antarctica and Greenland between 2003 and 2019. The melted ice has caused sea levels to rise 14mm in just 16 years.
Links to further reading
by Trevor Phillips
Extracted from FoGCV Newsletter 71, May 2020