CO2-induced heat source changes over the Tibetan Plateau in boreal summer-part II: the effects of CO2 direct radiation and uniform sea surface warming

Under the global warming, the influence of increased CO2 on regional climate change is driven by two main effects: CO2 direct radiation and oceanic warming. Based on the outputs of CMIP5 (phase 5 of the Coupled Model Intercomparison Project), the present study found that CO2 direct radiation and uniform oceanic warming are mainly responsible for the heat source (HS) enhancement led by increased CO2 during June–September over the Tibetan Plateau (TP). As CO2 increases, the resulting uniform sea surface warming induces atmospheric warming and increased atmospheric moisture over the TP, which locally enhances the latent heating (LH). In addition, the uniform sea surface warming narrows the land-sea thermal contrast between the Asian continent and the Indo-Pacific and reduces the ascending motion of the air over the TP. This reduction of ascending motion is offsetted by the effect of CO2 direct radiation, which enhances the thermal contrast and the ascending motion. The combined effect of the two causes a generally mild change in ascending motion. Evaporation intensification led by uniform sea surface warming partly contributes to the LH increase. Thus, the changes in LH lead to the enhancement of the TP HS. Additionally, the net radiation of the atmosphere over the TP slightly increases and partly hinders the HS increase, which is mainly associated with the effect of uniform sea surface warming. The leading intermodel spread of the TP HS features an overall positive/negative deviation pattern relative to the multi-model ensemble (MME) mean response caused by the LH diversity, which stems from the uncertainties of uniform sea surface warming and the corresponding temperature response over the TP among the models.