Differing responses of precipitation in Northern Hemisphere mid-latitudes to increased black carbon aerosols and carbon dioxide

As the most important contributors to global warming in recent decades, anthropogenic carbon dioxide (CO₂) and black carbon (BC) play significant roles in driving the global/regional hydrological cycle. Most of previous studies on the climate effects of CO₂ and BC focused on tropics and monsoon regions. The influences and their differences of CO₂ and BC on the precipitation in Northern Hemisphere mid-latitudes (NHML) have not been paid enough attention. Here we investigate the NHML precipitation responses to a tenfold increase in BC and a doubling of CO₂ by analyzing the multi-model simulation results from the Precipitation Driver Response Model Intercomparison Project (PDRMIP). Our results show that the NHML precipitation changes induced by BC and CO₂ distinctly differ in trends and seasons. The increased BC will reduce the NHML precipitation, especially in summer, whereas the doubled CO₂ will enhance the regional precipitation, mainly in winter. The differences between the BC and CO₂ induced NHML precipitation changes are most distinct in Central Asia and central North America. Further analyses reveal the underlying mechanisms of the distinct responses of precipitation: the decrease in NHML precipitation induced by BC aerosols mainly results from the dynamic effect by reducing the temperature gradient, thereby weakening the zonal wind, while the increased precipitation by CO₂ is caused by the increase in atmospheric water vapor through the thermodynamic effect. The results of these simulations are helpful for understanding the mechanism of anthropogenic precipitation changes in mid-latitudes.