A long-standing problem in state-of-the-art climate models is the Tropical Atlantic (TA) warm sea surface temperature (SST) bias, which goes along with major biases in large-scale atmospheric circulation. Here we show that TA-sector climate changes forced by increasing atmospheric carbon dioxide (CO₂) levels are sensitive to model resolution. Two versions of a climate model employing greatly varying atmospheric resolution and exhibiting very different warm bias strength are compared. The version with high atmospheric resolution features a small SST bias and simulates an eastward amplified SST warming over the equatorial Atlantic, in line with the observed SST trends since the mid-20th century. On the contrary, the version with coarse atmospheric resolution exhibits a large SST bias and projects relatively uniform SST changes across the equatorial Atlantic. In both model versions, the warming pattern resembles the pattern of interannual SST variability simulated under present-day conditions. Atmospheric changes also vastly differ among the two climate model versions. In the version with small SST bias, a deep atmospheric response is simulated with a major change in the Walker circulation and strongly enhanced rainfall over the equatorial region, whereas the atmospheric response is much weaker and of rather different character in the model with large SST bias. This study suggests that higher atmospheric resolution in climate models may enhance global warming projections over the TA sector.

在最新的气候模型中，长期存在的问题是热带大西洋（TA）暖海表面温度（SST）偏差，该偏差与大规模大气环流中的主要偏差一起出现。在这里，我们表明，由于大气中二氧化碳（CO ₂）级别对模型分辨率敏感。比较了两种版本的气候模型，这些模型采用了变化很大的大气分辨率并表现出非常不同的暖偏强度。具有高大气分辨率的版本具有较小的SST偏差，并且模拟了自20世纪中叶以来观测到的SST趋势，并向赤道大西洋向东放大了SST变暖。相反，大气分辨率较粗糙的版本表现出较大的SST偏差，并且在整个赤道大西洋上投射出相对均匀的SST变化。在两个模型版本中，变暖模式都类似于当前条件下模拟的年际SST变异性模式。两种气候模式版本之间的大气变化也存在很大差异。在SST偏差较小的版本中，在Walker环流发生重大变化并在赤道区域强烈增加降雨的情况下，模拟了深层大气响应，而在具有较大的SST偏差的模型中，大气响应要弱得多，并且具有不同的特征。这项研究表明，气候模型中更高的大气分辨率可能会增强TA部门对全球变暖的预测。