Dry ice is frozen Carbon Dioxide, or CO2, which is a gas under standard temperature and pressure conditions. The atmosphere contains about .035% of this gas. CO2 is a greenhouse gas, which means it absorbs light at infrared wavelengths. An increase in the concentration of this gas would, some scientists believe, cause an increase in the atmosphere's average temperature. The high concentration of CO2 in the atmosphere of the planet Venus is said to contribute to that planet's high average temperature.