When marine heatwaves and ocean acidity extreme events co-occur, it can have severe impacts on marine ecosystems. Researchers have determined for the first time the frequency and drivers of these compound events and have projected them into the future.When marine heatwaves and ocean acidity extreme events co-occur, it can have severe impacts on marine ecosystems. Researchers have determined for the first time the frequency and drivers of these compound events and have projected them into the future.