Response of atmospheric carbon dioxide to the secular variation of weakening geomagnetic field in whole atmosphere simulations

Responses of atmospheric carbon dioxide (CO 2 ) density to geomagnetic secular variation are investigated using the Whole Atmosphere Community Climate Model‐eXtended (WACCM‐X). Our ensemble simulations show that CO 2 volume mixing ratios (VMRs) increase at high latitudes and decrease at mid and low latitudes by several ppmv in response to a 50% weakening of the geomagnetic field. Statistically significant changes in CO 2 are mainly found above ~90 km altitude and primarily redetermine the energy budget at ~100‐110 km. Our analysis of transformed Eulerian mean (TEM) circulation found that CO 2 change is caused by enhanced upwelling at high latitudes and downwelling at mid and low latitudes as a result of increased Joule heating. We further analyzed the atmospheric CO 2 response to realistic geomagnetic weakening between 1978 and 2013, and found increasing (decreasing) CO 2 VMRs at high latitudes (mid and low latitudes) accordingly. For the first time, our simulation results demonstrate that the impact of geomagnetic variation on atmospheric CO 2 distribution is noticeable on a time scale of decades.