Abstract. The mid-Pliocene Warm Period (mPWP; ~3.2 million years ago) is seen as the most recent time period characterized by a warm climate state, with similar modern geography and ~400 ppmv atmospheric CO₂ concentration, and is therefore often considered an interesting analogue for near-future climate projections. Paleoenvironmental reconstructions indicate higher surface temperatures, decreasing tropical deserts, and a more humid climate in West Africa characterized by a strengthened West African Monsoon (WAM). Using model results from the second phase of the Pliocene Modelling Intercomparison Project (PlioMIP2) ensemble we analyze changes of the WAM rainfall during the mPWP, by comparing with the control simulations for the pre-industrial period. The ensemble shows a robust increase of the summer rainfall over West Africa and the Sahara region with an average increase of 2.7 mm/day, contrasted by a rainfall decrease over the equatorial Atlantic. An anomalous warming of the Sahara Desert and deepening of the Saharan Heat Low, seen in > 90 % of the models, leads to a strengthening of the WAM and an increased monsoonal flow into the continent. A similar warming of the Sahara Desert is seen in future projections using both phase 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5), and though previous studies of future projections indicate a west/east drying/wetting contrast over Sahel, PlioMIP2 simulations indicate a uniform rainfall increase over Sahel in warm climates characterized by increasing greenhouse gas forcing.

中文翻译：

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在PlioMIP2集合中模拟的上新世中期西非季风降雨

摘要。上新世中期暖期（mPWP；〜320万年前）被认为是一个以温暖的气候状态为特征的最新时期，具有类似的现代地理环境和〜400 ppmv的大气CO ₂集中度，因此通常被认为是近期气候预测的有趣模拟。古环境重建表明西非季风（WAM）增强，西非的地表温度升高，热带沙漠减少，气候更加潮湿。使用上新世建模比较项目（PlioMIP2）第二阶段的模型结果，通过与工业化前期的控制模拟进行比较，分析了mPWP期间WAM降雨的变化。该集合显示西非和撒哈拉地区的夏季降水强劲增加，平均每天增加2.7毫米/天，而赤道大西洋的降水减少。撒哈拉沙漠的异常变暖和撒哈拉低气压的加深，在> 90％的模型导致WAM的增强和进入大陆的季风流量增加。使用耦合模型比较项目（CMIP3和CMIP5）的第三和第五阶段，在未来的预测中可以看到类似的撒哈拉沙漠变暖，尽管先前对未来预测的研究表明，萨赫勒地区的东西向干燥/湿润对比，PlioMIP2模拟表明，在温暖的气候下，萨赫勒地区的降雨均匀增加，其特征是温室气体强迫增加。