Aragonese castle - Castello Aragonese by pe_ha45 on Flickr.

A few hundred yards from the preceding scene, CO₂ bubbling from seafloor vents acidifies the water to levels that might one day prevail all over the oceans. Dull mats of algae replace the colorful diversity—"fair warning,“ says biologist Jason Hall-Spencer.

Read what anthropogenic acidification is doing to our oceans and how, by 2100, this scene could be widespread: The Acid Sea