The breakthrough

The Paris Agreement was ratified in 2016, making it a pivotal year for the world's climate

The Paris Agreement happened in December 2015 in a blur of diplomatic activity - and you might think climate slipped down the agenda in the months after. Not so. To ensure the treaty enters legal force and starts as scheduled in 2021, the pact needed to be signed and then ratified by member states. Getting that done took up much of 2016. First came the signatures. At a UN event in April, leaders from 175 nations put their names to the deal. Their number has since risen to 197. Ratification was the next priority. The Paris Agreement was to take legal effect 30 days after at least 55 nations representing 55% of global emissions had ratified it, though provisions only become binding from 2020,