Use transform_first=True for contourf plots with Robinson projection

esmvaltool/cmorizers/data/formatters/datasets/cmap.py

@@ -25,8 +25,8 @@
 from pathlib import Path
 
 import iris
-from esmvaltool.cmorizers.data import utilities as utils
 
+from esmvaltool.cmorizers.data import utilities as utils
 
 logger = logging.getLogger(__name__)
 

esmvaltool/diag_scripts/monitor/multi_datasets.py

@@ -1169,6 +1169,9 @@ def _plot_map_with_ref(self, plot_func, dataset, ref_dataset):
             # Options used for all subplots
             projection = self._get_map_projection()
             plot_kwargs = self._get_plot_kwargs(plot_type, dataset)
+            if plot_func is iris.plot.contourf:
+                # see https://github.com/SciTools/cartopy/issues/2457
+                plot_kwargs['transform_first'] = True
             gridline_kwargs = self._get_gridline_kwargs(plot_type)
             fontsize = self.plots[plot_type]['fontsize']
 
@@ -1268,6 +1271,9 @@ def _plot_map_without_ref(self, plot_func, dataset):
             axes = fig.add_subplot(projection=self._get_map_projection())
             plot_kwargs = self._get_plot_kwargs(plot_type, dataset)
             plot_kwargs['axes'] = axes
+            if plot_func is iris.plot.contourf:
+                # see https://github.com/SciTools/cartopy/issues/2457
+                plot_kwargs['transform_first'] = True
             plot_map = plot_func(cube, **plot_kwargs)
             axes.coastlines()
             gridline_kwargs = self._get_gridline_kwargs(plot_type)

esmvaltool/diag_scripts/shared/plot/_plot.py

@@ -228,6 +228,7 @@ def global_contourf(cube,
     if cbar_range is not None:
         levels = np.linspace(*cbar_range)
         kwargs['levels'] = levels
+    kwargs['transform_first'] = True  # see SciTools/cartopy/issues/2457
     axes = plt.axes(projection=ccrs.Robinson(central_longitude=10))
     plt.sca(axes)
     map_plot = iris.plot.contourf(cube, **kwargs)