The 2018 spring edition of Variations is themed "Expansion of the tropics" and focuses on the magnitude, cause, and impacts of the recent expansion of the tropical belt region. The articles present some of the most pressing research questions, ideas for standardizing methods, the role of anthropo... Show moreThe 2018 spring edition of Variations is themed "Expansion of the tropics" and focuses on the magnitude, cause, and impacts of the recent expansion of the tropical belt region. The articles present some of the most pressing research questions, ideas for standardizing methods, the role of anthropogenic and natural variability, and how widening varies by region with different impacts over land and the ocean. Show less