Influence of Droughts on Mid-Tropospheric CO2

Using CO_2 data from the Atmospheric Infrared Sounder (AIRS), it is found for the first time that the mid-tropospheric CO_2 concentration is ~1 part per million by volume higher during dry years than wet years over the southwestern USA from June to September. The mid-tropospheric CO_2 differences between dry and wet years are related to circulation and CO_2 surface fluxes. During drought conditions, vertical pressure velocity from NCEP2 suggests that there is more rising air over most regions, which can help bring high surface concentrations of CO_2 to the mid-troposphere. In addition to the circulation, there is more CO_2 emitted from the biosphere to the atmosphere during droughts in some regions, which can contribute to higher concentrations of CO_2 in the atmosphere. Results obtained from this study demonstrate the significant impact of droughts on atmospheric CO_2 and therefore on a feedback cycle contributing to greenhouse gas warming. It can also help us better understand atmospheric CO_2, which plays a critical role in our climate system.