Atmospheric carbon dioxide concentration is expected to exceed 500 parts per million and global temperatures to rise by at least 2°C by 2050 to 2100, values that significantly exceed those of at least the past 420,000 years during which most extant marine organisms evolved. Under conditions expected in the 21st century, global warming and ocean acidification will compromise carbonate accretion, with corals becoming increasingly rare on reef systems.

The result will be less diverse reef communities and carbonate reef structures that fail to be maintained.

A century of phytoplankton decline suggests that ocean ecosystems are in peril.

Marine phytoplankton — the vast range of tiny algae species accounting for roughly half of Earth's total photosynthetic biomass — have declined substantially in the world's oceans over the past century, researchers report in Nature1 this week. The findings add to concerns that climate change is dangerously altering marine ecosystems.