The California wildfires of October 2017 were one of the largest wildfires in the state's history. Using surface temperature, surface pressure, cloud liquid and ice water contents, precipitation data, and wind data, we explore possible reasons for the wildfires. It is found that the mean surface temperature in California has increased, while mean cloud water contents and mean precipitation in California has decreased over the past 39 years. Higher temperatures, higher surface pressures, lower cloud water contents, lower precipitation, enhanced surface Santa Ana winds, and enhanced sinking air have set up favorable meteorological conditions for stronger wildfires in California, such as the October 2017 wildfires. Furthermore, the CO2 data from the Orbiting Carbon Observatory 2 satellite have, for the first time, made it possible for us to quantitatively characterize the impact of wildfires on atmospheric CO2 in California, which revealed that atmospheric CO2 increased by 2 ppm after the October 2017 California wildfires. Analyses in this study can help us better understand the causes and impacts of wildfires.