Figure 6.15
Atmospheric CO2 concentrations since 1000 CE. (A) Scientists take ice cores from the Greenland and Antarctic ice sheets in segments (shown here). When the segments are placed end to end, the cores are up to 3 km (2 mi) long. Scientists then carefully analyze ancient gas bubbles preserved in the ice. (B) Ancient air from ice cores provides a basis for comparison with the chemistry of today’s atmosphere.