With the release of his encyclical “Laudato Si” on Thursday, Pope Francis made headlines for recognizing the threat of human-caused climate change.
But the encyclical also called attention to the world’s oceans, affirming just how vital they are to “our common home.” In Laudato Si, Francis talked about the unique threats marine environments face in a planet changed by humanity.
Below are six warnings from the Pope about the health of our oceans. Quotes from the encyclical are shown in italics, along with their corresponding passage number.
The polar plight
“The melting in the polar ice caps and in high altitude plains can lead to the dangerous release of methane gas, while the decomposition of frozen organic material can further increase the emission of carbon dioxide.” 
Global warming is happening at a greater degree at Earth’s poles in a dangerous positive feedback cycle advanced by the high reflectivity of ice. As white, energy-reflecting snow and ice melts, it becomes darker, energy-absorbing water and land. If left uncurbed, warming will melt polar permafrost, unlocking frozen, ancient carbon and accelerating climate change.
Sea level rise
“A rise in the sea level…can create extremely serious situations, if we consider that a quarter of the world’s population lives on the coast or nearby, and that the majority of our megacities are situated in coastal areas.” 
Scientists say sea level rise could reach as much as six feet by the end of the century. Rising sea levels have already encroached upon island communities like Kiribati, leaving little land to live on and leaving citizens faced with the likelihood of becoming the world’s first climate refugees. And here in the U.S., sea level rise also leads to more frequent flooding and more severe coastal storm damage.
“Carbon dioxide pollution increases the acidification of the oceans and compromises the marine food chain. If present trends continue, this century may well witness…an unprecedented destruction of ecosystems, with serious consequences for all of us.” 
The ocean absorbs at least one quarter of emitted carbon dioxide, which increases the acidity of seawater through chemical reactions. Many marine species are highly sensitive to these changes, as they can only tolerate narrow ranges of pH. Oysters, clams and other shellfish are especially vulnerable because acidification make it more difficult for them to form the calcium carbonate that comprises their shells. Corals also struggle to build their skeletons in acidified water, to the detriment of the highly diverse array of species that depend on coral reefs.
Ocean-bound water pollution
“Underground water sources in many places are threatened by the pollution produced in certain mining, farming and industrial activities, especially in countries lacking adequate regulation or controls. It is not only a question of industrial waste. Detergents and chemical products, commonly used in many places of the world, continue to pour into our rivers, lakes and seas.” 
The eight million tons of plastic waste entering our oceans each year can entangle, starve or poison marine life, while agricultural pollution has led to downstream nutrient and bacterial contamination at levels unsafe for human exposure, also causing massive dead zones in coastal waters around the globe in which sea life cannot exist. Chemical and heavy metal pollution from household or industrial products, mining, and emissions from burning fossil fuels threaten human and marine health, too.
Overfishing and seafood bycatch
“Marine life in rivers, lakes, seas and oceans, which feeds a great part of the world’s population, is affected by uncontrolled fishing, leading to a drastic depletion of certain species. Selective forms of fishing which discard much of what they collect continue unabated. Particularly threatened are marine organisms which we tend to overlook, like some forms of plankton; they represent a significant element in the ocean food chain, and species used for our food ultimately depend on them.” 
According to the World Wildlife Foundation, roughly three billion people depend on seafood as their primary source of protein, particularly in developing countries. That’s why fishing practices like overfishing, dynamite fishing, and bycatch — the incidental catch of non-target species — are so destructive. Pope Francis’ effort to call attention to this problem reflects his understanding that sustainable fishing is, at its root, a food security issue as much as an environmental one.
Loss of marine biodiversity
“In tropical and subtropical seas, we find coral reefs comparable to the great forests on dry land, for they shelter approximately a million species, including fish, crabs, mollusks, sponges and algae. Many of the world’s coral reefs are already barren or in a state of constant decline.” 
“Wetlands converted into cultivated land lose the enormous biodiversity which they formerly hosted. In some coastal areas the disappearance of ecosystems sustained by mangrove swamps is a source of serious concern.” 
Biodiversity is a mark of a healthy, productive, and balanced ecosystem. Coral reefs and coastal mangrove ecosystems are among the most biodiverse environments on the planet, but as pollution, acidification, warming, and habitat destruction take their toll, the resources these special ecosystems provide deteriorate too. Healthy mangroves, for example, protect against storm surges, serve as habitat for commercially important seafood, and fight climate change by storing carbon.
With a reminder that “the oceans not only contain most of the planet, but also most of the wide variety of living things,” Pope Francis’s encyclical is a wake up call for all humanity to serve as responsible stewards not just of our lands and atmosphere, but of our vast blue realm as well.
Elise Shulman is a communications associate for Oceans at the Center for American Progress. Michael Conathan, also of the Center, contributed to this report.