How do we know what pre-industrial greenhouse gases and temperatures were?
Scientists have reconstructed past climate conditions through evidence preserved in tree rings, coral reefs and ice cores. For example, ice cores removed from 2 miles deep in the Antarctic contain atmospheric samples trapped in tiny air bubbles that date as far back as 650,000 years. These samples have allowed scientists to construct a historical record of greenhouse gas concentration and temperature stretching back hundreds of thousands of years.
