What is the relationship between temperature and CO2 concentration during glacial periods?

• A. Both temperature and CO2 concentrations are at their lowest levels.
• B. Temperature is high while CO2 is low
• C. Temperature is low but CO2 is high
• D. Temperature and CO2 are both at their highest levels

Answer: (A)

During glacial periods the climate is cooler and ice sheets are extensive. The ocean also holds more dissolved CO2 when it is colder, and changes in ocean circulation and biology reduce the amount of CO2 that escapes to the atmosphere. Ice-core records show atmospheric CO2 concentrations drop to low levels during these cold phases, while temperatures stay low. Because CO2 is a greenhouse gas, the lower atmospheric CO2 lowers the greenhouse effect, helping to maintain the cooler climate. Although the CO2 signal can lag behind initial temperature changes in the sequence of glacial cycles, the net state during a glacial period is a combination of low temperature and low CO2. This is why the best relationship to describe glacial periods is that both temperature and CO2 are at their lowest levels.