The rise of the seas is one of the most reliably measured consequences of global warming. Since satellite measurements began in 1993, the global average has risen by around ten centimeters – and the pace is accelerating: while the annual rate of increase was around 2.1 millimeters in the early 1990s, it will have doubled to around 4.5 millimeters by 2024. In the long term, two thirds of this is due to the melting of ice sheets and glaciers, and one third is due to the expansion of water as it warms up. In the exceptional year of 2024, this relationship was reversed because the ocean warmed unusually.
