Answer to Question 1
When glacial ice forms from snow, bubbles of air are trapped inside the ice. These bubbles are archives of the past atmosphere composition. Scientists measure the carbon dioxide concentrations in the bubbles. The age of each analyzed sample is determined by observing the annual layering in the ice.
Answer to Question 2
The greenhouse effect refers to the observation that many gas molecules in the atmosphere absorb the long-wave radiation emitted by Earth's surface and radiate most of this energy back toward the surface, which keeps Earth's surface much warmer than the temperature at the top of the atmosphere. The principal greenhouse gases are water vapor, carbon dioxide, methane, ozone, and nitrous oxide.
Climate Controls: A Summary
Climate Change
Carbon Isotope ratio
Global climate change and CO2 concentration
Stakeholders on all sides of the climate debate
Coal pollutes the atmosphere