MADRID — On the opening day of this year’s United Nations climate summit, or COP25, U.N. Secretary General António Guterres delivered a gut punch: “We are knowingly destroying the very support systems keeping us alive.”

One of those vital systems are the world’s oceans, which generate at least 50% of all oxygen in Earth’s atmosphere and have absorbed an estimated 93% of the excess heat from human-caused climate change. In September, the U.N.’s Intergovernmental Panel on Climate Change, or IPCC, published a groundbreaking report warning that warming poses a dire threat to our oceans.

The year’s summit is the first-ever “Blue COP,” a nod to the key role oceans play in regulating global climate. Chile, a leader in protecting ocean resources through the establishment of marine protected areas, gave the COP the official designation when it was still planning to host the event in Santiago. The South American country ultimately backed out amid civil unrest. Although Spain stepped in as host, Chile is still presiding over the conference, where parties to the landmark 2015 Paris climate agreement are working to finalize rules and technical details of the deal.

“For the first time, we bring the oceans to the table,” Carolina Schmidt, president of COP25 and Chile’s environmental minister, said during a press conference. “Oceans cover two-thirds of our planet. The only way we will increase ambition is if we consider how we protect our oceans.”

Madrid might be a landlocked city some 200 miles from the coast, but that hasn’t kept oceans from being a primary focus. The “Blue COP” label highlights a growing recognition that protecting marine environments is essential to tackling the climate crisis, and vice versa. Oceans and the many threats they now face ― warming, acidification, overfishing and pollution, to name a few ― have been front and center at the two-week summit, which runs through Dec. 13.

And it could be the first time the parties adopt a decision that includes a section on oceans.

Climate change is already wreaking havoc on ocean ecosystems and the coastal communities that rely on them. In Australia, for example, ocean heat waves triggered back-to-back bleaching events in 2016 and 2017 that wiped out an astonishing 50% of corals in the Great Barrier Reef.

The impacts will only worsen as atmospheric carbon dioxide levels climb. Countries like Egypt, Indonesia, Mexico and Thailand could lose over 95% of coral reef tourism revenue by 2100 under high emissions scenarios, while fish stocks in some West African countries could decline by 85%, according to a study released Friday at COP25 and commissioned by the High Level Panel for a Sustainable Ocean Economy, a group of government heads from 14 countries. The oceans are also rapidly losing oxygen, as detailed in a separate landmark report this week from the International Union for Conservation of Nature. This phenomenon, known as deoxygenation, is largely attributed to climate change and nutrients from pollution runoff. The number of ocean regions with low oxygen levels has soared from 45 in the 1960s to 700 today, with potential impacts ranging from fish mortality events and shifting migration patterns to the loss of entire ocean species, the IUCN found.

“There is no such thing as a healthy planetary ecosystem without a healthy ocean ecosystem,” Peter Thomson, the U.N. secretary general’s special envoy for the ocean, said at an event Saturday. Greenhouse gas emissions are “the enemy” of ocean health, and therefore of human existence, he said.

The Madrid summit has brought together thousands of ocean experts and advocates from dozens of countries. It features more than 100 side events and exhibits on the sea. At the start of the summit, Chile launched a new international initiative to put the ocean, the largest carbon sink on the planet, to use in the fight against rapidly worsening climate change. The European Union and Spain each held an “Ocean Day” at their conference pavilions. International leaders touted their own countries efforts to better safeguard marine areas. And scientists and NGOs have rolled out several new ocean reports and initiatives.

Scientists and advocates say this year’s event has helped elevate oceans to their proper place in the climate conversation. But a bigger push is to integrate ocean issues into the United Nations Framework Convention on Climate Change and have countries use oceans as a tool to meet emissions reduction targets.

Ahead of the talks, Indonesia, Fiji, Costa Rica and other countries proposed ocean-specific language that could end up in a final COP decision. The document calls on an advisory body of the UNFCCC to “convene a dialogue on the ocean-climate nexus” during its upcoming session in June ― a move that could officially bring oceans into future party negotiations.

Draft text of this year’s agreement released on Sunday includes language from the Indonesia proposal, although that could change as conversations are ongoing. Gwynne Taraska, director of the climate program at the Washington, D.C.-based nonprofit Ocean Conservancy, said she’s optimistic it will remain, as the proposal has so far had broad support.

“Government for a long time have overlooked the importance of ocean issues in the global climate effort,” Taraska said Monday. “I think it is starting to change though. Even over the past year or two, we’ve seen a kind of burgeoning ocean climate movement.”

Of course, what oceans need most is for world governments to rapidly move away from fossil fuels.

Our understanding of ocean ecosystems has come a long way since climate change came into clearer focus in the 1970s and ’80s. For a long time, the perception was that oceans were simply too vast to be altered by human activity, said Ove Hoegh-Guldberg, a climate scientists and coral reef expert from Australia.

Hoegh-Guldberg co-authored the new ocean economy impacts analysis, which builds upon an IPCC report last year that found 70 to 90% of the world’s tropical reefs could be wiped out if the planet warms 1.5 degrees Celsius (2.7 degrees Fahrenheit) above preindustrial levels. (Earth temperature has already climbed 1.1 degrees Celsius). At 2 degrees warming, upward of 99% of remaining corals could perish. The IPCC estimates that climate-induced ocean damage could cost the global economy $428 billion annually by 2050 and nearly $2 trillion by 2100.

“The entire ocean is changing,” Hoegh-Guldberg told HuffPost. “We better get off this pathway now, very quickly, otherwise we are going to commit ourselves to thousands of years of mayhem.”