As a scientist who spent a career studying the ocean, I am alarmed, but not surprised, by the new United Nations report on the implications of climate change for oceans and Earth’s ice masses. As humankind increases concentrations of carbon dioxide and other greenhouse gases in the atmosphere, the world is warming. The oceans are storing most of this heat, resulting in more intense hurricanes, reduced oxygen levels and death of coral reefs. Polar ice sheets are now melting, raising ocean levels. The consequences will be very severe if we don’t act quickly to limit warming.