The world is in a period of rapid change. Climate chaos is leading to floods, droughts and exacerbating inequality. In this article, we ask, in such a context, what is the role of mathematics education and, in particular, what can mathematics teacher educators (MTEs) do in supporting teachers to respond to global challenges, and the associated injustices, within their mathematics classrooms? We review work done within critical mathematics education and develop a model for reflection on the role of the MTE. We report on work taking place in one university in the UK where, since 2015, MTEs have been encouraging teachers to address global issues in their classrooms. One role which has emerged for an MTE is in supporting the translation of scientific work on climate change into classroom tasks. In England, the spaces for such work are being squeezed in an education system increasingly subject to conservative political forces. We conclude the article by considering possibilities for MTEs to provoke a generic questioning of assumptions, which we argue is possible even within such constraints.