Issued in May 2015 ahead of the Paris climate summit later that year, Laudato Si, taking its title from a line of Francis of Assisi's Canticle of the Creatures praising God through Brother Sun and Sister Moon, was the first papal encyclical devoted entirely to the natural environment. Pope Francis argued that ecological degradation and human poverty were not separate problems but a single crisis, describing what he called an integral ecology in which care for the earth and care for the poor, who suffer environmental harm they did little to cause and have the fewest resources to escape, are inseparable moral obligations rather than competing priorities.
The encyclical drew explicitly on climate science, accepting the scientific consensus on human caused climate change as a starting point rather than a matter for theological dispute, a stance some political and religious commentators in various countries criticized as the church overstepping into a scientific and economic policy question, while others, including many scientists and environmental advocates outside the Catholic church entirely, welcomed it as a major moral voice entering the climate debate at a critical moment.
Laudato Si also criticized what Francis called a throwaway culture of excessive consumption, and market-first responses to ecological crisis that treat nature purely as a resource to be managed for profit rather than as a shared inheritance with its own claim on human responsibility, arguments he returned to and sharpened in a follow-up document, Laudate Deum, issued in 2023 as he judged the world's response to the original encyclical's warnings insufficient.