Climate change is likely to be one of the defining global issues of the 21st century. The past decade—the hottest in recorded history—has witnessed countries around the world struggling to deal with drought, heat waves, and extreme weather. The sheer scale of the problem also makes it hard to understand, predict, and solve. Climate science journals regularly publish special issues on specific climate models, typically timed to present results from a major new release of a given model. However, these tend to focus on the new science that the model enables, rather than to describe the software and its development. This special issue of IEEE Software magazine focuses on the "software" behind climate change models.