The world's oceans have reached their highest ever recorded temperature, with global average surface temperatures hitting 20.96C, well above the average for this time of year. Temperatures are likely to continue to increase, because the world's oceans are at their hottest in March.
Oceans have an essential role in regulating the planet's climate. They absorb heat, produce around half of the world's oxygen and have a key role in weather patterns too. As more excess heat is caused by the burning of fossil fuels, an increasing amount of heat is absorbed by the oceans. And warmer oceans have less ability to absorb carbon dioxide, making the impact of climate change even worse.
Ocean heatwaves cause marine species like fish and whales to look for cooler water, which can have serious impacts on marine food chains. Predators like sharks can become more aggressive in hotter water.
In the last 150 years - for which we have recorded ocean temperatures, global mean ocean temperatures have increased by 0.9C, with 0.6C of that increase happening in the last 40 years.
The previous record for ocean temperatures (20.95C) was set in 2016, when the last El Nino was at its most intense. El Nino is a natural phenomenon that occurs in cycles every two to seven years. Warm water rises to the surface to the west of South America, causing temperatures across the globe to rise.
But whilst 2016's temperatures were recorded at the height of El Nino, this year's new record comes as a new El Nino is just getting going. So it's quite possible that even higher ocean temperatures may be recorded in the coming months.
In waters around the UK, we saw sea temperatures 3C to 5C above the average, according to the European Space Agency and the Met Office. Meanwhile, waters off Florida recently reached 38C.